Why can't we kill ourselves by holding our breath?

Why can't we kill ourselves by holding our breath?

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Is it possible to kill yourself by holding your breath?

This question is obviously copied from Quora, but I had heard it as a fact that we cannot kill ourselves by holding our breath and I'm looking for a referenced answer.

Short answer
Healthy people cannot hold their breaths until unconsciousness sets in, let alone commit suicide.

According to Parkes (2005), a normal person cannot even hold their breath to unconsciousness, let alone death. Parkes says:

Breath‐holding is a voluntary act, but normal subjects appear unable to breath‐hold to unconsciousness. A powerful involuntary mechanism normally overrides voluntary breath‐holding and causes the breath that defines the breakpoint.

Parkes explains that voluntary breath‐holding does not stop the central respiratory rhythm. Instead, breath holding merely suppresses its expression by voluntarily holding the chest at a certain volume. At the time of writing, no simple explanation for the break point existed. It is known to be caused by partial pressures of blood gases activating the carotid arterial chemoreceptors. They are peripheral sensory neurons that detect changes in chemical concentrations, including low oxygen (hypoxia) and high carbon dioxide (hypercapnia). Both hypoxia and hypercapnia are signs of breath holding and both are detected by the chemoreceptors. These receptors send nerve signals to the vasomotor center of the medulla which eventually overrides the conscious breath holding.

The breaking point can be postponed by large lung inflations, hyperoxia and hypocapnia, and it is shortened by increased metabolic rates.

- Parkes, Exp Physiol (2006); 91(1): 1-15

Counterexample: At least some people can train themselves to hold their breath until they pass out, and if this occurs underwater they will almost certainly die by drowning.

When I was in military service I became friends with some U.S. Navy SEALs. They go through a notoriously difficult training and selection process (BUDS) that has been well documented. Among the program's "evolutions" are tests in which candidates have to solve problems to access SCUBA units while submerged in pools or water tanks (and while being harassed by instructors). It is common for candidates to pass out during these tests, because if they surface for air they fail the test. (And these are people who self-select as very motivated to not fail at any cost.) Apparently the tests weed out candidates who are prone to panic as they lose oxygen and can't override their physiological instinct to breath.

I spoke to one graduate who passed out during one such evolution (but succeeded on a second attempt). He noted that after that incident he lost any fear of drowning, because he realized that if he ever found himself in a situation where he was running out of oxygen he would not feel panic and would just fall unconscious before drowning.

Ignoring Your Emotions Is Bad for Your Health. Here's What to Do About It

M odern life is full of emotional challenges. The pressure to succeed, need to “keep up,” fear of missing out and desire for good relationships and work satisfaction can all evoke volatile combinations of emotions.

However, what we learn in our society is not how to work with our emotions, but how to block and avoid them. We do it quite well: Between alcohol use, prescription drug use and screen time, there are a multitude of ways to avoid our feelings. When we do acknowledge them, we swat them away with mantras learned since childhood. (“Mind over matter,” “get a grip” and “suck it up” are familiar ones.) Thwarting emotions is not good for mental or physical health. It&rsquos like pressing on the gas and brakes of your car at the same time, creating an internal pressure cooker.

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What Happens When You Hold Your Breath Too Long?

When a person holds his breath in for too long, the amount of carbon dioxide in his body begins to accumulate, according to The Science Creative Quarterly. He may start feeling a burning sensation in his lungs.

When the level of carbon dioxide becomes too high, painful contractions begin in the ribs and in the diaphragm. The pain is a signal that the person needs to exhale. The body and brain start to suffer from a lack of oxygen. The critical line refers to the moment when a person accumulates so much carbon dioxide in his body that he begins to feel pain. Hyperventilating is one way to delay the critical line moment, but hyperventilating is also dangerous, notes The Science Creative Quarterly. Hyperventilation can result in unconsciousness because it undermines the body's signals to breathe.

The effects of breath holding on the brain are not yet clear, according to The New York Times. Scientists from the University of Queensland conducted neuropsychological tests on free divers to examine the way their brains behaved compared to people who did not free dive. They found that the free divers' brains responded normally in visual, language and recall tests. A SPECT brain scan showed some abnormalities in five free divers' brains, but scientists were uncertain of the significance of the findings.

ELI5: Why can't you suffocate by holding your breath?

I haven't meant to kill myself by holding my breath. But everyone has tried to hold it for as long as possible yet no matter how long we do it for we always suddenly take a breath. It is some kind of reflex action?

If you do it long enough you will pass out and start breathing again (assuming you don't hit your head on the way down), but most of the time your Britain will just go "nope" and force you to breath

Autocorrect! Your BRAIN not Britain.

You'll eventually pass out and your body will breathe on its own at that point, just as if you were sleeping. You keep breathing.

There are several mechanisms in action here. When you hold your breath for a period of time, your body is unable to get rid of carbon dioxide, which is a natural byproduct of metabolism. Certain sensory cells in the carotid arteries detect this elevated level of CO2 and send impulses to your brain stem (the area of the brain that regulates breathing). Your brain stem gives you the impulse to breathe. The higher the concentration of CO2 in your blood, the stronger the respiration impulse becomes. Most people will give in to this impulse and exhale before taking a breath. Exhalation gets rid of some CO2 and the breathing impulse lowers to normal after several subsequent breaths.

If you are determined enough to resist the breathing impulse, it is possible to continue to hold your breath until the oxygen concentration in your blood is not high enough for your brain to properly function. At this point you will lose consciousness. Once you pass out, you can no longer consciously hold your breath and your body automatically regulates breathing and all that CO2 is blown off and O2 levels normalize again.

It is very difficult to make yourself pass out though. Your body is very sensitive to CO2 levels, compared to O2 levels. I've personally had a pulse oximeter on my finger and have held my breath as long as I could tolerate. After about 50 seconds of not breathing, my oxygen saturation was still 99% but the urge to breathe overwhelmed me and I had to take a breath.

Oxygen and carbon dioxide

During breath-holding, the arterial or end tidal partial pressure of oxygen P falls below its normal level of ∼100 mmHg and that of carbon dioxide P rises above its normal level of ∼40 mmHg. At breakpoint from maximum inflation in air, the P is typically 62 ± 4 mmHg and the P is typically 54 ± 2 mmHg (n= 5 Lin et al. 1974 ), and the longer the breath-hold the more they change. It is remarkable that adults normally cannot breath-hold consistently to unconsciousness, even under laboratory supervision. Nunn (1987) estimates that consciousness in normal adults is lost at P levels below ∼27 mmHg and P levels between 90 and 120 mmHg. Breakpoint levels close to these have been reported, e.g. P levels as low as 24 mmHg, P levels as high as 91 mmHg and breath-hold durations of 14 min or more ( Schneider, 1930 Ferris et al. 1946 Klocke & Rahn, 1959 ). For comparison, Schneider (1924, 1930) extraordinarily describes surreptitiously switching subjects' breathing to inspire from a spirometer of N2 (and to exhale to room air) and measuring (Fig. 1b) the range of breathing times to impending unconsciousness (cyanosis, mask-like facial expression, pupil dilation, eye convergence, falling systolic pressure Schneider & Truesdell, 1923 ). This range is similar to his range of breath-hold durations (Fig. 1a), yet such symptoms are not characteristic of the breakpoint of breath-holding.

One obvious hypothesis to explain the breakpoint is that once P falls below or P rises above a certain threshold partial pressure, or rate of change of partial pressure reaches a threshold, then chemoreceptor stimulation causes an involuntary breath. The presumption has always been that these would be carotid chemoreceptors [aortic chemoreceptors have no demonstrable effect on breathing in humans ( Lugliani et al. 1971 Wasserman et al. 1975 )]. As the following paragraphs show, this ‘arterial chemoreceptor hypothesis’ is supported by the pronounced effects on breath-hold duration of altering the composition of the inspired gas. It is, however, confounded by the lack of a consistent pattern of arterial gas pressures at breakpoint, by denervation of carotid chemoreceptors failing to prolong breath-holds until unconsciousness and by the ability to breath-hold repeatedly after inspiring asphyxiating gas mixtures.

Breath-hold duration is almost doubled by breath-holding with hyperoxic gas mixtures (Fig. 5c), or by preceding breath-holding by voluntary or mechanical hyperventilation to lower P levels (Fig. 5a). Incidentally, preoxygenation has many practical advantages in studying breath-holding. Not only does it prolong duration, it also results in heart rate barely changing throughout the breath-hold ( Gross et al. 1976 ) and in breakpoints that do not occur at P levels low enough to threaten the brain. [Strictly, there is a risk of atelectasis with breath-holds when the lungs contain 100% O2 ( Campbell et al. 1967 ), so some dilution with nitrogen is preferable.]

Alternatively, breath-hold duration is almost halved by breath-holding from hypoxia (Fig. 5c), or from hypercapnia, e.g. raising the inspired P to 65 mmHg ( Godfrey & Campbell, 1969 Kelman & Wann, 1971 ).

The arterial chemoreceptor hypothesis, however, is not supported by the known blood gas pressures at breakpoint. Thus, preoxygenation does not prolong breath-hold duration until mean P falls to ca. 62 mmHg. Instead, the breakpoint occurs while P is still remarkably elevated, e.g. 553 ± 16 mmHg, n= 5 ( Lin et al. 1974 ). Conversely, hypoxia does not shorten breath-hold duration until P falls to 62 mmHg. Instead the breakpoint occurs at the even lower P values of 24–43 mmHg ( Ferris et al. 1946 ). Similarly, hypercapnia does not shorten breath-hold duration until P rises to 54 mmHg ( Kelman & Wann, 1971 ) and P can reach 70 mmHg ( Godfrey & Campbell, 1969 ). Furthermore, the breakpoint of breath-holds from hypocapnia occurs at P levels between 48 ± 3 ( Cooper et al. 2003 ) and 71 ± 3 mmHg ( Klocke & Rahn, 1959 ). Nor is the breakpoint at some unique combination of low P and high P ( Klocke & Rahn, 1959 ). Indeed, even after the longest possible breath-holds from hypocapnia with preoxygenation, blood gas levels at breakpoint are remarkably benign.

In humans, the carotid bodies provide the only known means of detecting arterial hypoxia ( Lugliani et al. 1971 Wasserman et al. 1975 ) and of rapidly detecting arterial hypercapnia. The arterial chemoreceptor hypothesis is further opposed by the fact that a breakpoint still occurs following carotid chemodenervation (resection), i.e. denervation does not prolong breath-holding until unconsciousness. Davidson and coworkers ( Davidson et al. 1974 Gross et al. 1976 ) compared breath-hold duration at inspiratory capacity in five patients following bilateral carotid body resection with that of normal subjects (Fig. 5b). Mean breath-hold duration in 100% O2 was almost no different and there were no functionally important differences at breakpoint in their mean P levels [362 ± 20 versus 425 ± 12 mmHg (mean ± s.e.m. ) in controls], nor in mean P levels [59 ± 2 versus 56 ± 4 mmHg(mean ± s.e.m. )]. There can, however, be some ambiguity in interpreting these breath-hold duration data, because they can also be used to show that carotid body denervation does produce a small increase in breath-hold duration, confirmed by ( Honda et al. 1988 ). Figure 5b shows that mean breath-hold duration in denervated patients in 21% O2 is 54% longer (P < 0.05) than in intact subjects and that in 12% O2 it is 65% longer (P < 0.05). Nevertheless, if the carotid chemoreceptors are the only means of detecting hypoxia, what mechanism explains how hypoxia continues to shorten breath-hold duration in denervated patients? Possibly, this shortening still occurs because the important action of hypoxia is not on carotid chemoreceptors but is on diaphragm muscle chemoreceptors ( Road, 1990 Jammes & Speck, 1995 ), whose stimulation may instead make an important contribution to the breakpoint (see section entitled Paralysis of the diaphragm).

Do central chemoreceptors mediate the breakpoint? Their role during breath-holding is still unclear. In as much as PaCO2 reflects their level of stimulation during breath-holding, the lack of a consistent PaCO2 level at breakpoint suggests not. Yet the facts that breath-hold duration in 5 patients with apparently no functional peripheral or central chemoreceptivity (congenital central hypoventilation syndrome- Shea et al., 1993 ) is almost double that of 5 age and gender matched controls, and that 4/5 had to be told to break by the experimenters, suggests otherwise.

Deadly Fungi Are the Newest Emerging Microbe Threat All Over the World

Maryn McKenna is a journalist specializing in public health, global health, and food policy and a senior fellow at the Center for the Study of Human Health at Emory University. She is author, most recently, of Big Chicken: The Incredible Story of How Antibiotics Created Modern Agriculture and Changed the Way the World Eats (National Geographic Books, 2017).
Credit: Nick Higgins


Maryn McKenna is a journalist specializing in public health, global health, and food policy and a senior fellow at the Center for the Study of Human Health at Emory University. She is author, most recently, of Big Chicken: The Incredible Story of How Antibiotics Created Modern Agriculture and Changed the Way the World Eats (National Geographic Books, 2017).

I t was the fourth week of June in 2020, and the middle of the second wave of the COVID pandemic in the U.S. Cases had passed 2.4 million deaths from the novel coronavirus were closing in on 125,000. In his home office in Atlanta, Tom Chiller looked up from his e-mails and scrubbed his hands over his face and shaved head.

Chiller is a physician and an epidemiologist and, in normal times, a branch chief at the U.S. Centers for Disease Control and Prevention, in charge of the section that monitors health threats from fungi such as molds and yeasts. He had put that specialty aside in March when the U.S. began to recognize the size of the threat from the new virus, when New York City went into lockdown and the CDC told almost all of its thousands of employees to work from home. Ever since, Chiller had been part of the public health agency's frustrating, stymied effort against COVID. Its employees had been working with state health departments, keeping tabs on reports of cases and deaths and what jurisdictions needed to do to stay safe.

Shrugging off exhaustion, Chiller focused on his in-box again. Buried in it was a bulletin forwarded by one of his staff that made him sit up and grit his teeth. Hospitals near Los Angeles that were handling an onslaught of COVID were reporting a new problem: Some of their patients had developed additional infections, with a fungus called Candida auris. The state had gone on high alert.

Chiller knew all about C. auris&mdashpossibly more about it than anyone else in the U.S. Almost exactly four years earlier he and the CDC had sent an urgent bulletin to hospitals, telling them to be on the lookout. The fungus had not yet appeared in the U.S., but Chiller had been chatting with peers in other countries and had heard what happened when the microbe invaded their health-care systems. It resisted treatment by most of the few drugs that could be used against it. It thrived on cold hard surfaces and laughed at cleaning chemicals some hospitals where it landed had to rip out equipment and walls to defeat it. It caused fast-spreading outbreaks and killed up to two thirds of the people who contracted it.

Shortly after that warning, C. auris did enter the U.S. Before the end of 2016, 14 people contracted it, and four died. Since then, the CDC had been tracking its movement, classifying it as one of a small number of dangerous diseases that doctors and health departments had to tell the agency about. By the end of 2020 there had been more than 1,500 cases in the U.S., in 23 states. And then COVID arrived, killing people, overwhelming hospitals, and redirecting all public health efforts toward the new virus and away from other rogue organisms.

But from the start of the pandemic, Chiller had felt uneasy about its possible intersection with fungal infections. The first COVID case reports, published by Chinese scientists in international journals, described patients as catastrophically ill and consigned to intensive care: pharmaceutically paralyzed, plugged into ventilators, threaded with I.V. lines, loaded with drugs to suppress infection and inflammation. Those frantic interventions might save them from the virus&mdashbut immune-damping drugs would disable their innate defenses, and broad-spectrum antibiotics would kill off beneficial bacteria that keep invading microbes in check. Patients would be left extraordinarily vulnerable to any other pathogen that might be lurking nearby.

Chiller and his colleagues began quietly reaching out to colleagues in the U.S. and Europe, asking for any warning signs that COVID was allowing deadly fungi a foothold. Accounts of infections trickled back from India, Italy, Colombia, Germany, Austria, Belgium, Ireland, the Netherlands and France. Now the same deadly fungi were surfacing in American patients as well: the first signs of a second epidemic, layered on top of the viral pandemic. And it wasn't just C. auris. Another deadly fungus called Aspergillus was starting to take a toll as well.

&ldquoThis is going to be widespread everywhere,&rdquo Chiller says. &ldquoWe don't think we're going to be able to contain this.&rdquo

We are likely to think of fungi, if we think of them at all, as minor nuisances: mold on cheese, mildew on shoes shoved to the back of the closet, mushrooms springing up in the garden after hard rains. We notice them, and then we scrape them off or dust them away, never perceiving that we are engaging with the fragile fringes of a web that knits the planet together. Fungi constitute their own biological kingdom of about six million diverse species, ranging from common companions such as baking yeast to wild exotics. They differ from the other kingdoms in complex ways. Unlike animals, they have cell walls unlike plants, they cannot make their own food unlike bacteria, they hold their DNA within a nucleus and pack cells with organelles&mdashfeatures that make them, at the cellular level, weirdly similar to us.* Fungi break rocks, nourish plants, seed clouds, cloak our skin and pack our guts, a mostly hidden and unrecorded world living alongside us and within us.

In September 2018 Torrence Irvin of Patterson, Calif., felt like he had picked up a cold. Seven months later he had lost 75 percent of his lung capacity. Irvin had Valley fever, a fungal infection, and his life was saved by an experimental drug. Credit: Timothy Archibald

That mutual coexistence is now tipping out of balance. Fungi are surging beyond the climate zones they long lived in, adapting to environments that would once have been inimical, learning new behaviors that let them leap between species in novel ways. While executing those maneuvers, they are becoming more successful pathogens, threatening human health in ways&mdashand numbers&mdashthey could not achieve before.

Surveillance that identifies serious fungal infections is patchy, and so any number is probably an undercount. But one widely shared estimate proposes that there are possibly 300 million people infected with fungal diseases worldwide and 1.6 million deaths every year&mdashmore than malaria, as many as tuberculosis. Just in the U.S., the CDC estimates that more than 75,000 people are hospitalized annually for a fungal infection, and another 8.9 million people seek an outpatient visit, costing about $7.2 billion a year.

For physicians and epidemiologists, this is surprising and unnerving. Long-standing medical doctrine holds that we are protected from fungi not just by layered immune defenses but because we are mammals, with core temperatures higher than fungi prefer. The cooler outer surfaces of our bodies are at risk of minor assaults&mdashthink of athlete's foot, yeast infections, ringworm&mdashbut in people with healthy immune systems, invasive infections have been rare.

That may have left us overconfident. &ldquoWe have an enormous blind spot,&rdquo says Arturo Casadevall, a physician and molecular microbiologist at the Johns Hopkins Bloomberg School of Public Health. &ldquoWalk into the street and ask people what are they afraid of, and they'll tell you they're afraid of bacteria, they're afraid of viruses, but they don't fear dying of fungi.&rdquo

Ironically, it is our successes that made us vulnerable. Fungi exploit damaged immune systems, but before the mid-20th century people with impaired immunity didn't live very long. Since then, medicine has gotten very good at keeping such people alive, even though their immune systems are compromised by illness or cancer treatment or age. It has also developed an array of therapies that deliberately suppress immunity, to keep transplant recipients healthy and treat autoimmune disorders such as lupus and rheumatoid arthritis. So vast numbers of people are living now who are especially vulnerable to fungi. (It was a fungal infection, Pneumocystis carinii pneumonia, that alerted doctors to the first known cases of HIV 40 years ago this June.)

Not all of our vulnerability is the fault of medicine preserving life so successfully. Other human actions have opened more doors between the fungal world and our own. We clear land for crops and settlement and perturb what were stable balances between fungi and their hosts. We carry goods and animals across the world, and fungi hitchhike on them. We drench crops in fungicides and enhance the resistance of organisms residing nearby. We take actions that warm the climate, and fungi adapt, narrowing the gap between their preferred temperature and ours that protected us for so long.

But fungi did not rampage onto our turf from some foreign place. They were always with us, woven through our lives and our environments and even our bodies: every day, every person on the planet inhales at least 1,000 fungal spores. It is not possible to close ourselves off from the fungal kingdom. But scientists are urgently trying to understand the myriad ways in which we dismantled our defenses against the microbes, to figure out better approaches to rebuild them.

I t is perplexing that we humans have felt so safe from fungi when we have known for centuries that our crops can be devastated from their attacks. In the 1840s a funguslike organism, Phytophthora infestans, destroyed the Irish potato crop more than one million people, one eighth of the population, starved to death. (The microbe, formerly considered a fungus, is now classified as a highly similar organism, a water mold.) In the 1870s coffee leaf rust, Hemileia vastatrix, wiped out coffee plants in all of South Asia, completely reordering the colonial agriculture of India and Sri Lanka and transferring coffee production to Central and South America. Fungi are the reason that billions of American chestnut trees vanished from Appalachian forests in the U.S. in the 1920s and that millions of dying Dutch elms were cut out of American cities in the 1940s. They destroy one fifth of the world's food crops in the field every year.

Yet for years medicine looked at the devastation fungi wreak on the plant kingdom and never considered that humans or other animals might be equally at risk. &ldquoPlant pathologists and farmers take fungi very seriously and always have, and agribusiness has,&rdquo says Matthew C. Fisher, a professor of epidemiology at Imperial College London, whose work focuses on identifying emerging fungal threats. &ldquoBut they're very neglected from the point of view of wildlife disease and also human disease.&rdquo

So when the feral cats of Rio de Janeiro began to fall ill, no one at first thought to ask why. Street cats have hard lives anyway, scrounging, fighting and birthing endless litters of kittens. But in the summer of 1998, dozens and then hundreds of neighborhood cats began showing horrific injuries: weeping sores on their paws and ears, clouded swollen eyes, what looked like tumors blooming out of their faces. The cats of Rio live intermingled with humans: Children play with them, and especially in poor neighborhoods women encourage them to stay near houses and deal with rats and mice. Before long some of the kids and mothers started to get sick as well. Round, crusty-edge wounds opened on their hands, and hard red lumps trailed up their arms as though following a track.

In 2001 researchers at the Oswaldo Cruz Foundation, a hospital and research institute located in Rio, realized they had treated 178 people in three years, mostly mothers and grandmothers, for similar lumps and oozing lesions. Almost all of them had everyday contact with cats. Analyzing the infections and ones in cats treated at a nearby vet clinic, they found a fungus called Sporothrix.

The various species of the genus Sporothrix live in soil and on plants. Introduced into the body by a cut or scratch, this fungus transforms into a budding form resembling a yeast. In the past, the yeast form had not been communicable, but in this epidemic, it was. That was how the cats were infecting one another and their caretakers: Yeasts in their wounds and saliva flew from cat to cat when they fought or jostled or sneezed. Cats passed it to humans via claws and teeth and caresses. The infections spread from skin up into lymph nodes and the bloodstream and to eyes and internal organs. In case reports amassed by doctors in Brazil, there were accounts of fungal cysts growing in people's brains.

The fungus with this skill was decreed a new species, Sporothrix brasiliensis. By 2004, 759 people had been treated for the disease at the Cruz Foundation by 2011, the count was up to 4,100 people. By last year, more than 12,000 people in Brazil had been diagnosed with the disease across a swath of more than 2,500 miles. It has spread to Paraguay, Argentina, Bolivia, Colombia and Panama.

&ldquoThis epidemic will not take a break,&rdquo says Flávio Queiroz-Telles, a physician and associate professor at the Federal University of Paraná in Curitiba, who saw his first case in 2011. &ldquoIt is expanding.&rdquo

It was a mystery how: Feral cats wander, but they do not migrate thousands of miles. At the CDC, Chiller and his colleagues suspected a possible answer. In Brazil and Argentina, sporotrichosis has been found in rats as well as cats. Infected rodents could hop rides on goods that move into shipping containers. Millions of those containers land on ships docking at American ports every day. The fungus could be coming to the U.S. A sick rat that escaped a container could seed the infection in the city surrounding a port.

&ldquoIn dense population centers, where a lot of feral cats are, you could see an increase in extremely ill cats that are roaming the streets,&rdquo says John Rossow, a veterinarian at the CDC, who may have been the first to notice the possible threat of Sporothrix to the U.S. &ldquoAnd being that we Americans can't avoid helping stray animals, I imagine we're going to see a lot of transmission to people.&rdquo

To a mycologist such as Chiller, this kind of spread is a warning: The fungal kingdom is on the move, pressing against the boundaries, seeking any possible advantage in its search for new hosts. And that we, perhaps, are helping them. &ldquoFungi are alive they adapt,&rdquo he says. Among their several million species, &ldquoonly around 300 that we know of cause human disease&mdashso far. That's a lot of potential for newness and differentness, in things that have been around for a billion years.&rdquo

Torrence Irvin was 44 years old when his fungal troubles started. A big healthy man who had been an athlete in high school and college, he lives in Patterson, Calif., a quiet town in the Central Valley tucked up against U.S. Route 5. A little more than two years earlier Irvin had bought a house in a new subdivision and moved in with his wife, Rhonda, and their two daughters. He was a warehouse manager for the retailer Crate & Barrel and the announcer for local youth football games.

In September 2018 Irvin started to feel like he had picked up a cold he couldn't shake. He dosed himself with Nyquil, but as the weeks went on, he felt weak and short of breath. On a day in October, he collapsed, falling to his knees in his bedroom. His daughter found him. His wife insisted they go to the emergency room.

Doctors thought he had pneumonia. They sent him home with antibiotics and instructions to use over-the-counter drugs. He got weaker and couldn't keep food down. He went to other doctors, while steadily getting worse, enduring shortness of breath, night sweats, and weight loss similar to a cancer victim's. From 280 pounds, he shrank to 150. Eventually one test turned up an answer: a fungal infection called coccidioidomycosis, usually known as Valley fever. &ldquoUntil I got it, I had never heard of it,&rdquo he says.

But others had. Irvin was referred to the University of California, Davis, 100 miles from his house, which had established a Center for Valley Fever. The ailment occurs mostly in California and Arizona, the southern tip of Nevada, New Mexico and far west Texas. The microbes behind it, Coccidioides immitis and Coccidioides posadasii, infect about 150,000 people in that area every year&mdashand outside of the region the infection is barely known. &ldquoIt's not a national pathogen&mdashyou don't get it in densely populated New York or Boston or D.C.,&rdquo says George R. Thompson, co-director of the Davis center and the physician who began to supervise Irvin's care. &ldquoSo even physicians view it as some exotic disease. But in areas where it's endemic, it's very common.&rdquo

Similar to Sporothrix, Coccidioides has two forms, starting with a thready, fragile one that exists in soil and breaks apart when soil is disturbed. Its lightweight components can blow on the wind for hundreds of miles. Somewhere in his life in the Central Valley, Irvin had inhaled a dose. The fungus had transformed in his body into spheres packed with spores that migrated via his blood, infiltrating his skull and spine. To protect him, his body produced scar tissue that stiffened and blocked off his lungs. By the time he came under Thompson's care, seven months after he first collapsed, he was breathing with just 25 percent of his lung capacity. As life-threatening as that was, Irvin was nonetheless lucky: in about one case out of 100, the fungus grows life-threatening masses in organs and the membranes around the brain.

Irvin had been through all the approved treatments. There are only five classes of antifungal drugs, a small number compared with the more than 20 classes of antibiotics to fight bacteria. Antifungal medications are so few in part because they are difficult to design: because fungi and humans are similar at the cellular level, it is challenging to create a drug that can kill them without killing us, too.

It is so challenging that a new class of antifungals reaches the market only every 20 years or so: the polyene class, including amphotericin B, in the 1950s the azoles in the 1980s and the echinocandin drugs, the newest remedy, beginning in 2001. (There is also terbinafine, used mostly for external infections, and flucytosine, used mostly in combination with other drugs.)

For Irvin, nothing worked well enough. &ldquoI was a skeleton,&rdquo he recalls. &ldquoMy dad would come visit and sit there with tears in his eyes. My kids didn't want to see me.&rdquo

In a last-ditch effort, the Davis team got Irvin a new drug called olorofim. It is made in the U.K. and is not yet on the market, but a clinical trial was open to patients for whom every other drug had failed. Irvin qualified. Almost as soon as he received it, he began to turn the corner. His cheeks filled out. He levered himself to his feet with a walker. In several weeks, he went home.

Valley fever is eight times more common now than it was 20 years ago. That period coincides with more migration to the Southwest and West Coast&mdashmore house construction, more stirring up of soil&mdashand also with increases in hot, dry weather linked to climate change. &ldquoCoccidioides is really happy in wet soil it doesn't form spores, and thus it isn't particularly infectious,&rdquo Thompson says. &ldquoDuring periods of drought, that's when the spores form. And we've had an awful lot of drought in the past decade.&rdquo

Because Valley fever has always been a desert malady, scientists assumed the fungal threat would stay in those areas. But that is changing. In 2010 three people came down with Valley fever in eastern Washington State, 900 miles to the north: a 12-year-old who had been playing in a canyon and breathed the spores in, a 15-year-old who fell off an ATV and contracted Valley fever through his wounds, and a 58-year-old construction worker whose infection went to his brain. Research published two years ago shows such cases might become routine. Morgan Gorris, an earth systems scientist at Los Alamos National Laboratory, used climate-warming scenarios to project how much of the U.S. might become friendly territory for Coccidioides by the end of this century. In the scenario with the highest temperature rise, the area with conditions conducive to Valley fever&mdasha mean annual temperature of 10.7 degrees Celsius (51 degrees Fahrenheit) and mean annual rainfall of less than 600 millimeters (23.6 inches)&mdashreaches to the Canadian border and covers most of the western U.S.

Irvin has spent almost two years recovering he still takes six pills of olorifim a day and expects to do that indefinitely. He gained back weight and strength, but his lungs remain damaged, and he has had to go on disability. &ldquoI am learning to live with this,&rdquo he says. &ldquoI will be dealing with it for the rest of my life.&rdquo

Deadly duo of fungi is infecting more people. Coccidioides immitis causes Valley fever, and its range is spreading beyond the Southwest, where it was first identified (top). Aspergillus fumigatus appears in many environments and can be lethal to people suffering from the flu or COVID (bottom). Credit: Science Source

S porothrix found a new way to transmit itself. Valley fever expanded into a new range. C. auris, the fungus that took advantage of COVID, performed a similar trick, exploiting niches opened by the chaos of the pandemic.

That fungus was already a bad actor. It did not behave the way that other pathogenic yeasts do, living quiescently in someone's gut and surging out into their blood or onto mucous membranes when their immune system shifted out of balance. At some point in the first decade of the century, C. auris gained the ability to directly pass from person to person. It learned to live on metal, plastic, and the rough surfaces of fabric and paper. When the first onslaught of COVID created a shortage of disposable masks and gowns, it forced health-care workers to reuse gear they usually discard between patients, to keep from carrying infections. And C. auris was ready.

In New Delhi, physician and microbiologist Anuradha Chowdhary read the early case reports and was unnerved that COVID seemed to be an inflammatory disease as much as a respiratory one. The routine medical response to inflammation would be to damp down the patient's immune response, using steroids. That would set patients up to be invaded by fungi, she realized. C. auris, lethal and persistent, had already been identified in hospitals in 40 countries on every continent except Antarctica. If health-care workers unknowingly carried the organism through their hospitals on reused clothing, there would be a conflagration.

&ldquoI thought, &lsquoOh, God, I.C.U.s are going to be overloaded with patients, and infection-control policies are going to be compromised,'&rdquo she said recently. &ldquoIn any I.C.U. where C. auris is already present, it is going to play havoc.&rdquo

Chowdhary published a warning to other physicians in a medical journal early in the pandemic. Within a few months she wrote an update: a 65-bed I.C.U. in New Delhi had been invaded by C. auris, and two thirds of the patients who contracted the yeast after they were admitted with COVID died. In the U.S., the bulletin that Chiller received flagged several hundred cases in hospitals and long-term care facilities in Los Angeles and nearby Orange County, and a single hospital in Florida disclosed that it harbored 35. Where there were a few, the CDC assumed that there were more&mdashbut that routine testing, their keyhole view into the organism's stealthy spread, had been abandoned under the overwork of caring for pandemic patients.

As bad as that was, physicians familiar with fungi were watching for a bigger threat: the amplification of another fungus that COVID might give an advantage to.

In nature, Aspergillus fumigatus serves as a clean-up crew. It encourages the decay of vegetation, keeping the world from being submerged in dead plants and autumn leaves. Yet in medicine, Aspergillus is known as the cause of an opportunistic infection spawned when a compromised human immune system cannot sweep away its spores. In people who are already ill, the mortality rate of invasive aspergillosis hovers near 100 percent.

During the 2009 pandemic of H1N1 avian flu, Aspergillus began finding new victims, healthy people whose only underlying illness was influenza. In hospitals in the Netherlands, a string of flu patients arrived unable to breathe and going into shock. In days, they died. By 2018 what physicians were calling invasive pulmonary aspergillosis was occurring in one out of three patients critically ill with flu and killing up to two thirds of them.

Then the coronavirus arrived. It scoured the interior lung surface the way flu does. Warning networks that link infectious disease doctors and mycologists around the globe lit up with accounts of aspergillosis taking down patients afflicted with COVID: in China, France, Belgium, Germany, the Netherlands, Austria, Ireland, Italy and Iran. As challenging a complication as C. auris was, Aspergillus was worse. C. auris lurks in hospitals. The place where patients were exposed to Aspergillus was, well, everywhere. There was no way to eliminate the spores from the environment or keep people from breathing them in.

In Baltimore, physician Kieren Marr was acutely aware of the danger. Marr is a professor of medicine and oncology at Johns Hopkins Medical Center and directs its unit on transplant and oncology infectious diseases. The infections that take hold in people who have received a new organ or gotten a bone marrow transplant are familiar territory for her. When COVID arrived, she was concerned that Aspergillus would surge&mdashand that U.S. hospitals, not alert to the threat, would miss it. Johns Hopkins began testing COVID patients in its I.C.U. with the kind of molecular diagnostic tests used in Europe, trying to catch up to the infection in time to try to treat it. Across the five hospitals the Johns Hopkins system operates, it found that one out of 10 people with severe COVID was developing aspergillosis.

Several patients died, including one whose aspergillosis went to the brain. Marr feared there were many others like that patient, across the country, whose illness was not being detected in time. &ldquoThis is bad,&rdquo Marr said this spring. &ldquoAspergillus is more important in COVID right now than C. auris. Without a doubt.&rdquo

The challenge of countering pathogenic fungi is not only that they are virulent and sneaky, as bad as those traits may be. It is that fungi have gotten very good at protecting themselves against drugs we use to try to kill them.

The story is similar to that of antibiotic resistance. Drugmakers play a game of leapfrog, trying to get in front of the evolutionary maneuvers that bacteria use to protect themselves from drugs. For fungi, the tale is the same but worse. Fungal pathogens gain resistance against antifungal agents&mdashbut there are fewer drugs to start with, because the threat was recognized relatively recently.

&ldquoIn the early 2000s, when I moved from academia to industry, the antifungal pipeline was zero,&rdquo says John H. Rex, a physician and longtime advocate for antibiotic development. Rex is chief medical officer of F2G, which makes the not yet approved drug that Torrence Irvin took. &ldquoThere were no antifungals anywhere in the world in clinical or even preclinical development.&rdquo

That is no longer the case, but research is slow as with antibiotics, the financial rewards of bringing a new drug to market are uncertain. But developing new drugs is critical because patients may need to take them for months, sometimes for years, and many of the existing antifungals are toxic to us. (Amphotericin B gets called &ldquoshake and bake&rdquo for its grueling side effects.) &ldquoAs a physician, you're making a choice to deal with a fungal infection at the cost of the kidney,&rdquo says Ciara Kennedy, president and CEO of Amplyx Pharmaceuticals, which has a novel antifungal under development. &ldquoOr if I don't deal with the fungal infection, knowing the patient's going to die.&rdquo

Developing new drugs also is critical because the existing ones are losing their effectiveness. Irvin ended up in the olorofim trial because his Valley fever did not respond to any available drugs. C. auris already shows resistance to drugs in all three major antifungal classes. Aspergillus has been amassing resistance to the antifungal group most useful for treating it, known as the azoles, because it is exposed to them so persistently. Azoles are used all across the world&mdashnot only in agriculture to control crop diseases but in paints and plastics and building materials. In the game of leapfrog, fungi are already in front.

The best counter to the ravages of fungi is not treatment but prevention: not drugs but vaccines. Right now no vaccine exists for any fungal disease. But the difficulty of treating patients long term with toxic drugs, combined with staggering case numbers, makes finding one urgent. And for the first time, one might be in sight if not in reach.

The reason that rates of Valley fever are not worse than they are, when 10 percent of the U.S. population lives in the endemic area, is that infection confers lifelong immunity. That suggests a vaccine might be possible&mdashand since the 1940s researchers have been trying. A prototype that used a killed version of the form Coccidioides takes inside the body&mdashfungal spheres packed with spores&mdashworked brilliantly in mice. But it failed dismally in humans in a clinical trial in the 1980s.

&ldquoWe did it on a shoestring, and everyone wanted it to work,&rdquo says John Galgiani, now a professor and director of the Valley Fever Center for Excellence at the University of Arizona College of Medicine, who was part of that research 40 years ago. &ldquoEven with [bad] reactions and the study lasting three years, we kept 95 percent of the people who enrolled.&rdquo

Enter dogs. They have their noses in the dirt all the time, and that puts them at more at risk of Valley fever than humans are. In several Arizona counties, close to 10 percent of dogs come down with the disease every year, and they are more likely to develop severe lung-blocking forms than human are. They suffer terribly, and it is lengthy and expensive to treat them. But dogs' vulnerability&mdashplus the lower standards that federal agencies require to approve animal drugs compared with human ones&mdashmakes them a model system for testing a possible vaccine. And the passion of owners for their animals and their willingness to empty their wallets when they can may turn possibility into reality for the first time.

Galgiani and his Arizona group are now working on a new vaccine formula, thanks to financial donations from hundreds of dog owners, plus a boost from a National Institutes of Health grant and commercial assistance from a California company, Anivive Lifesciences. Testing is not complete, but it could reach the market for use in dogs as early as next year. &ldquoI think this is proof of concept for a fungal vaccine&mdashhaving it in use in dogs, seeing it is safe,&rdquo says Lisa Shubitz, a veterinarian and research scientist at the Arizona center. &ldquoI really believe this is the path to a human vaccine.&rdquo

This injection does not depend on a killed Valley fever fungus. Instead it uses a live version of the fungus from which a gene that is key to its reproductive cycle, CPS1, has been deleted. The loss means the fungi are unable to spread. The gene was discovered by a team of plant pathologists and later was identified in Coccidioides by Marc Orbach of the University of Arizona, who studies host-pathogen interactions. After creating a mutant Coccidioides with the gene removed, he and Galgiani experimentally infected lab mice bred to be exquisitely sensitive to the fungus. The microbe provoked a strong immune reaction, activating type 1 T helper cells, which establish durable immunity. The mice survived for six months and did not develop any Valley fever symptoms, even though the team tried to infect them with unaltered Coccidioides. When the researchers autopsied the mice at the end of that half-year period, scientists found almost no fungus growing in their lungs. That long-lasting protection against infection makes the gene-deleted fungus the most promising basis for a vaccine since Galgiani's work in the 1980s. But turning a vaccine developed for dogs into one that could be used in humans will not be quick.

The canine formula comes under the purview of the U.S. Department of Agriculture, but approval of a human version would be overseen by the U.S. Food and Drug Administration. It would require clinical trials that would probably stretch over years and involve thousands of people rather than the small number of animals used to validate the formula in dogs. Unlike the 1980s prototype, the new vaccine involves a live organism. Because there has never been a fungal vaccine approved, there is no preestablished evaluation pathway for the developers or regulatory agencies to follow. &ldquoWe would be flying the plane and building it at the same time,&rdquo Galgiani says.

He estimates achieving a Valley fever vaccine for people could take five to seven years and about $150 million, an investment made against an uncertain promise of earnings. But a successful compound could have broad usefulness, protecting permanent residents of the Southwest as well as the military personnel at 120 bases and other installations in the endemic area, plus hundreds of thousands of &ldquosnowbird&rdquo migrants who visit every winter. (Three years ago the CDC identified cases of Valley fever in 14 states outside the endemic zone. Most were in wintertime inhabitants of the Southwest who were diagnosed after they went back home.) By one estimate, a vaccine could save potentially $1.5 billion in health-care costs every year.

&ldquoI couldn't see the possibility that we'd have a vaccine 10 years ago,&rdquo Galgiani says. &ldquoBut I think it is possible now.&rdquo

I f one fungal vaccine is achieved, it would carve the path for another. If immunizations were successful&mdashscientifically, as targets of regulation and as vaccines people would be willing to accept&mdashwe would no longer need to be on constant guard against the fungal kingdom. We could live alongside and within it, safely and confidently, without fear of the ravages it can wreak.

But that is years away, and fungi are moving right now: changing their habits, altering their patterns, taking advantage of emergencies such as COVID to find fresh victims. At the CDC, Chiller is apprehensive.

&ldquoThe past five years really felt like we were waking up to a whole new phenomenon, a fungal world that we just weren't used to,&rdquo Chiller says. &ldquoHow do we stay on top of that? How do we question ourselves to look for what might come next? We study these emergences not as an academic exercise but because they show us what might be coming. We need to be prepared for more surprises.&rdquo

*Editor&rsquos Note (6/9/21): This sentence was revised after posting to correct the description of how the cells of fungi differ from those of animals.

This article was originally published with the title "Deadly Kingdom" in Scientific American 324, 6, 26-35 (June 2021)

The Ice Bucket Challenge Can Kill. Here's Why You're Doing It Wrong

The Ice Bucket Challenge has raised an impressive amount of money and awareness for motor neuron diseases like Amyotrophic Lateral Sclerosis (Lou Gehrig's Disease). In just one month, the ALS Association has received $80m in donations.

But while the fundraising campaign should be praised, the tragic death of a Scottish teenager reveals that the Ice Bucket Challenge can be dangerous – and potentially deadly.

When you imagine the dangers of cold water, you probably think of hypothermia. "There was a bit of a preoccupation with hypothermia dating right back to the Titanic, and then reinforced during the Second World War," says Professor Mike Tipton, a physiologist at the University of Portsmouth and co-author of Essentials Of Sea Survival.

But fatal hypothermia takes a relatively long time: starting from 37ºC/99ºF, it takes half an hour for your core body temperature to fall below 35ºC/95ºF.

Most deaths in open water occur within minutes, as two-thirds of drowning victims are good swimmers and over half die within 10 feet of safe refuge.

The first thing Ice Bucket challengers and those immersed in cold water experience is a sudden drop in skin temperature, which triggers a reflex called the cold shock response.

"It's basically exactly the same as you would imagine if you stepped or jumped into a pool they said was heated and it wasn't, or stepped under a shower that had just run cold," Tipton explains. "It's a gasp response followed by uncontrollable hyperventilation."

That gasp for air and rapid inhalation completely destroys your ability to hold your breath. Even if you can normally hold your breath for a minute in the bathtub, you would only last a few seconds in cold water. The average volume an adult inhales is 2-3 litres, and the lethal dose for drowning is 1.5 litres of seawater or 3 litres of freshwater.

If you're already underwater or waves are battering your face, the cold shock response could kill you.

There are many reasons why people lose their lives. Some can't swim while others succumb to flash floods, for example. But Tipton believes that many 'drowning' victims are actually being killed from immersion in cold water. He estimates that about 20% succumb to hypothermia, 20% of people die before, during or after being rescued (a phenomenon called circum-rescue collapse) and the remaining 60% are killed by the cold shock response.

The Ice Bucket Challenge has been linked with two deaths so far. The Scottish teenager, 18-year-old Cameron Lancaster, drowned after jumping into a flooded quarry. Another victim, 40-year-old father Willis Tepania from New Zealand, had a heart attack after drinking a bottle of bourbon.

(Although not a consequence of the challenge itself, Corey Griffin, a 27-year-old who raised $100,000 for his friend Pete Frates – the college baseball player with ALS who made the campaign go viral – died after diving into Nantucket Island harbor.)

Most Ice Bucket Challenge participants don't submerge themselves, so how can cold water immersion be dangerous to them? The problem occurs when you're holding your breath and your face gets wet.

Immersing yourself in cold water triggers two powerful physiological responses: cold shock and another reflex, the diving response.

Cold water becomes particularly dangerous when the two coincide. "If you've got those two responses co-activated then you've got a response trying to accelerate the heart – the cold shock response – at the same time as you've got a response trying to slow it down, the diving response," says Tipton.

He calls this 'autonomic conflict' because both the cold shock and diving responses send signals to the heart via nerves that control involuntary body functions (including breathing), the autonomic nervous system.

The diving response is vital to marine mammals such as seals and dolphins, but humans have it too.

It's the reflex that tells your heart to calm down and redirects blood flow to the most crucial organs, like the brain. It's what prompts you to hold your breath underwater and enables you to conserve oxygen.

Both the cold shock and diving responses are triggered by receptors in the skin – nerve endings of the autonomic system.

The diving response is stimulated by receptors on your face (near the eyes, nose and mouth) while cold shock is triggered by thermoreceptors all around the body. Because these nerve endings are 0.2mm below the surface of the skin, body fat – which insulates against hypothermia – won't stop you detecting a temperature drop.

When cold water is sensed by your face and rest of the body simultaneously, autonomic conflict is the result. Both the cold shock and diving responses relay sensory information (via the brain) to the heart, but their messages contradict each other. Submerge your face alone and heart rate should fall from the normal 60-100 to about 40-50 beats per minute, whereas cold water will boost the rate above 100.

To the heart, autonomic conflict is like pushing the gas pedal to accelerate while also vigorously and repeatedly applying the brakes.

Autonomic conflict creates an abnormal heart rhythm – arrhythmia – and can occasionally lead to the most dangerous outcome of cold water immersion: sudden cardiac death.

After releasing a held breath, an arrhythmia will start within 10 seconds, and this can be detected on an electrocardiogram (ECG). "I would be really interested in having an ECG on all these people who are doing the Ice Bucket Challenge because I pretty well guarantee there will be a fairly significant number of them having an arrhythmia while they do it," says Tipton.

Cardiac arrhythmias are common. If you swim or snorkel, you probably experience them regularly.

In Tipton's previous studies, 2% of fit and healthy subjects experienced an arrhythmia when their body was immersed in cold water, but the proportion goes up to 82% when the face is wet too. The problem gets worse in stressful situations: among people who train to escape from submerged helicopters, including those who work on offshore platforms or for the military, 25% have an arrhythmia during a 10-second drill.

On their own, most cardiac arrhythmias won't show symptoms and probably aren't hazardous to health, but other factors can predispose an individual to a lethal rhythm.

People with a pre-existing cardiovascular problems, such as a heart condition or hypertension, are at particular risk from sudden cardiac death – especially if those problems haven't been identified. Medicines (certain antihistamines, antibiotics and antipsychotic drugs) can also increase risk.

Even athletes aren't safe. Figures from 2003 to 2011 show that 30 out of 43 or 70% of fatal incidents during US triathlons occurred during the swim phase of a race. Because strong emotions like anger increase heart rate and athletes have no trouble while training alone, Tipton believes that competition (through mass starts and collisions) also raise the risk of arrhythmia. "These are all relatively young, fit individuals who are also having a problem with sudden cardiac death."

Autonomic conflict between the cold shock and diving responses might also be behind fatalities where cause of death has been misdiagnosed as hypothermia or drowning, because the electrical disturbances that lead to arrhythmia can't be detected in post-mortem examinations.

Sudden cardiac death is impossible to predict, but highlighting the dangers of cold water can help prevent more people dying from the Ice Bucket Challenge.

Most won't suffer from the symptoms of cardiac arrhythmia, but there's still a real risk that some will. All it takes is for one person to die and the money for worthy causes will quickly dry up.

Fundraising campaigns are a fun way to help charities, but some people – especially celebrities – must participate responsibly.

You could argue that rich celebrities should accept a forfeit instead of the dare. Charlie Sheen and Sir Patrick Stewart are great examples of this. On the other hand, the Ice Bucket Challenge probably wouldn't have gone viral if we didn't enjoy seeing others - especially famous people - in discomfort from being drenched by ice-cold water. It's pure Schadenfreude, that pleasure you get from someone else's misfortune.

Not using cold water removes the danger, but who wants to watch the Lukewarm Bucket Challenge?

Making the Ice Bucket Challenge safe is simple. Professor Mike Tipton's advice for minimising the chances of a heart attack is straightforward:

Participants should also avoid total immersion. "If you go into cold water then the physiological responses will be much more profound and prolonged than if you just have a bucket of water thrown over the top of your head."

Practicing breath focus

Breath focus helps you concentrate on slow, deep breathing and aids you in disengaging from distracting thoughts and sensations. It's especially helpful if you tend to hold in your stomach.

First steps. Find a quiet, comfortable place to sit or lie down. First, take a normal breath. Then try a deep breath: Breathe in slowly through your nose, allowing your chest and lower belly to rise as you fill your lungs. Let your abdomen expand fully. Now breathe out slowly through your mouth (or your nose, if that feels more natural).

Breath focus in practice. Once you've taken the steps above, you can move on to regular practice of controlled breathing. As you sit comfortably with your eyes closed, blend deep breathing with helpful imagery and perhaps a focus word or phrase that helps you relax.

Ways to elicit the relaxation response

Several techniques can help you turn down your response to stress. Breath focus helps with nearly all of them:

  • Progressive muscle relaxation , tai chi, and Qi Gong
  • Repetitive prayer
  • Guided imagery

How does soap work?

To fully understand the FDA’s ruling, we should first understand a little about how soaps clean and disinfect. A quick chemistry refresher will remind us that there are two general types of molecules: polar (things that can be mixed into water, like sugar) and nonpolar (things that cannot be mixed into water, like oil).

Soap molecules are amphipathic, meaning they have both polar and non-polar properties. This gives soap the ability to dissolve most types of molecules, making it easier to wash them off your hands (Figure 1). In terms of illness-causing germs, which are mostly bacteria and viruses, soap has a two-fold effect: one chemical and one behavioral. Firstly, the amphipathic nature of soap loosens the bacteria and viruses off your hands so they can be washed away more easily. Secondly, you tend to wash your hands for a longer period when using soap, because you try to rinse all of it away. Thus, regular soaps don’t necessarily kill bacteria and viruses as much as they simply help you wash them off your skin.

Figure 1:The amphipathic nature of soap molecules help lift dirt and bacteria off skin and into water so that they can be washed away.

Antibacterial soaps have all the same properties as regular soap, but with an extra ingredient added that is intended to stop the bacteria remaining on your skin from replicating. The idea is that this additive will further protect the hand-washer from harmful bacteria as compared to regular soap. It is important to mention that these ingredients generally have no effect on viruses, so the focus is to reduce the risk from bacterial germs. The most common antibacterial additive found in consumer hand soaps is a compound called triclosan.

Why Do We Inhale Oxygen And Exhale Carbon Dioxide?

Why do we inhale oxygen and exhale carbon dioxide? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Fabian van den Berg, Neuropsychologist, on Quora:

Why do we inhale oxygen and exhale carbon dioxide? Short and long answer, you ready?

The short answer is that you inhale oxygen because you need oxygen for some biological processes. A fairly important one is the production of ATP, the energy all of our cells use. In the process, electrons are used and oxygen has a high affinity for electrons. The waste products of this process are Carbon Dioxide and Water, in different steps along the way.

The long answer needs some pictures. This one is a seriously long answer and will explain the production of ATP. CO2 is involved in the citric acid cycle and water is involved in the electron transport chain.

You know how we eat to live? Well that’s where it starts. The major source of energy we get from food is sugar, more specifically glucose. Now things get a bit funky so bear with me. Glucose needs to be broken down in steps. This has to be done slowly because glucose contains plenty of energy and we don’t want to blow stuff up.

Step 1: Glycolysis

The glucose molecules are broken down into two pyruvate molecules. It takes ten steps to go from glucose to pyruvates. This all happens in the cytosol, which is all the fluid inside a cell between the organelles.

The big 6-carbon glucose molecule first needs to be split into two smaller 3-carbon molecules (phosphoglyceraldehyde, PGAL), this split uses ATP. It might sound counterproductive since we are trying to make ATP, but the investment will pay off. One ATP is used by each kinase reaction, and step one and step three require it, so a total of two ATPs are used to split glucose into the smaller PGAL molecules.

These PGAL molecules are then transformed into Pyruvate, and during that process two ADPs are turned into ATP by a kinase reaction (in steps seven and ten). Because we have two PGALs we create four ATPs (so we gain two because we used two before).

The whole process therefore uses glucose and two ATP and then produces two pyruvates, two NADH, and four ATP. The net gain is two ATP, the investment paid off since we doubled it.

Step 2: Pyruvate Oxidation / Decarboxylation / Pyruvate Dehydrogenase

In the last step we were left with pyruvate after breaking apart glucose, in fact we have two pyruvate molecules for each glucose model. The next step is Pyruvate Oxidation, which takes place inside mitochondria. Remember the famous saying: “Mitochondria are the powerhouses of the cell”? We’ll get there soon enough. The transformation takes place in a few steps.

  • The first step is breaking off a carbon molecule, this carbon takes two oxygens with it(so CO2 is removed).
  • In the second step the 2-carbon molecule that is left is oxidized (electrons lost), these electrons are picked up by the NAD+ turning it into NADH.
  • The 2-carbon molecule is attached to Coenzyme-A, this turns it into Acetyl CoA. This is just a carrier molecule to bring the 2-carbon group to the next step.

From one glucose molecule two pyruvate molecules are made, these are turned into two acetyl-CoA molecules. Two carbons are released as carbon dioxide, these are two carbons from the original six in glucose. Lastly, two NADH are produced from NAD+.

Step 3: The Citric Acid Cycle / Krebs cycle / Tricarboxylic Acid (TCA)

This cycle (whatever name you choose) is an essential step in the process. It takes the Acetyl-CoA produced in the last step and squeezes out every tiny bit of potential energy it can. Just like the last step this process takes place in the matrix of mitochondria. It’s called a cycle for a reason, the reason being that it is a closed loop. The last part reforms the molecule used in the first step.

  1. In the very first stage acetyl-CoA is combined with oxaloacetate (a 4-carbon molecule) into the 6-carbon molecule citrate (hence the name).
  2. In a two- stage process a water molecule is removed and added again to citrate to turn it into isocitrate.
  3. Then in a series of reactions it breaks of two carbon molecules, these are released as Carbon Dioxide. This happens in a similar manner as in Pyruvate Oxidation with the help of NAD+. This part of the cycle has a regulatory function, the enzymes doing this can speed up or slow down depending on energy needs. In the third step we are left with a 5-carbon molecule called a-ketoglutarate.
  4. In stage four we have a repeat of stage three, where a 4-carbon molecule is created, which is again hooked up to Coenzyme A to form Succinyl-CoA.
  5. We are now left with the 4-carbon molecule of Succinyl-CoA. The CoA part is replaced by a phosphate group, and the phosphate group then immediately transfers to ADP to make ATP. Some cells also use Guanine instead of Adenosine, turning GDP into GTP. These two are basically the same, energy carriers. What is left of the Succinyl is now Succinate.
  6. We are working with the Succinate now and in stage six it gets oxidized into fumarate, it loses 2 H+. The hydrogen atoms are transferred onto FAD, turning it into FADH2. FAD is used instead of NAD+ because Succinate doesn’t like to give away electrons. FAD has a higher electron affinity and is able to get them from Succinate, NAD+ is not strong enough. FADH2 production is done by an enzyme embedded into the inner membrane of the mitochondria, so the electrons go straight into the electron transport chain.
  7. In stage seven water is added to the fumarate, turning it into malate.
  8. Stage eight Oxidizes the Malate using NAD+ again, this results in Oxaloacetate the molecule we added in the first step.
  • In each cycle two carbons enter with Acetyl-CoA, two molecules of Carbon Dioxide are released in the process (in steps three and four).
  • Three NADH molecules are formed (in steps three, four, and eight), and one molecule of FADH2 (in step six).
  • One molecule of ATP/GTP is produced (in step five).

Per Glucose (two Acetyl-CoA are produced)

Step 4: Oxidative Phosphorylation

From the last step we have quite a lot of NADH and FADH2 molecules, the actual ATP produced by the Citric Acid Cycle isn’t a lot, but the important molecules are in fact this abundance of NADH and FADH2. This is what we are going to use in the last step, Oxidative Phosphorylation. This is actually a two stage process consisting of the Electron Transport Chain and Chemiosmosis.

Electron Transport Chain

The Electron Transport Chain is composed of several proteins and organic molecules that are embedded in the membrane of the mitochondria. These proteins are bundled together into complexes, four of them in this case.

We start with the NADH and FADH2 molecules that were created in the previous step. These are the ones we got via glycolysis, pyruvate oxidation, and then the citric acid cycle.

  1. In complex 1 NADH transfers its electrons, turning back into NAD+ and H+ which is moved to the intermembrane Space. The electrons are transferred to Ubiquinone (Q). FADH2 holds onto its electrons a bit tighter (they are at a lower energy level), so Complex 1 can’t do anything with it but pass it on.
  2. In Complex 2 the same thing happens to FADH2 using the same enzyme that made it during the citric cycle. The electrons are taken and passed onto Ubiquinone (Q) via iron-sulfur proteins.
  3. The electrons are now in Ubiquinone (Q), which in the process has become QH2­­ and travels through the membrane to deliver the electrons to Complex 3. Complex 3 uses the energy to pump more H+ into the intermembrane space.
  4. The electrons are passed on to another carrier: Cytochrome C (Cyt C), transporting them to complex 4. Complex 4 makes good use of the gradient and pumps a few more H+ across the membrane. The electrons eventually end up attached to O2 which splits up into separate oxygen atoms. The separate oxygen atoms then need Hydrogen to share a proton, and as we know oxygen plus hydrogen equals water (good old H2O).

So what happens is that NADH and FADH2 are turned back into NAD+ and FAD, we need this because they are required in glycolysis and the citric acid cycle. If they wouldn’t be turned back there wouldn’t be any available for the former cycles and the whole thing breaks down.

Secondly a gradient is created, H+ is pumped to the intermembrane space changing the concentrations and creating stored energy to be used later. It’s like winding up a toy, the winding stores energy to be released later.

The “waste” product is water Oxygen is used because it has a high affinity for the electrons. This is why we breath, we need the oxygen to take away the electrons at the end. If there is no oxygen to pick up the electrons the chain ends, production stops, and energy production grinds to a halt.

In the first stage protein complex 1, 2, and 3 actively pump H+ to the intermembrane space. With this difference in concentration of H+ a gradient is created, also called the proton-motive force (hydrogen/H+ are called protons). Because of the gradient H+ wants to move back into the matrix, like a ball wants to move downhill. But the membrane won’t allow the H+ to go, there is only one path it can take. A protein called ATP synthase forms a channel across the membrane. Similar to how a hydroelectric dam uses the force of water, the ATP Synthase protein uses the flow of H+. The process of using a proton gradient to do something is called chemiosmosis (hence the name).

When H+ flows through the protein the top part (poking out into the intermembrane space) turns, the base (inside the matrix) stays stationary. Turning the inner part inside the base grabs ADP and adds a Phosphate to it. In a sense the ADP is energized as ATP (you go from di-phosphate to tri-phosphate). For each 4 H+ ions that flows through the channel, a single ADP molecule is turned into ATP.

This is why the mitochondria are called “powerhouses of the cell”, this is almost a quite literal description of what is going on. Just like how a hydroelectric dam generates power for a town, ATP synthase creates the energy used by everything.

ATP Synthase is a true ATP monster, producing more than 80% of the ATP yield collected from breaking down glucose. This way each molecule of glucose yields an additional 26-28 ATP by using the gradient created by NADH and FADH2. The grand total of ATP produced for each glucose molecule is then about 30-32 ATP.

  • Two ATP are made in Glycolysis and two more are made during the Citric Acid Cycle. The rest comes from the NADH and FADH2 converted in the ATP synthase. When NADH moves through the transport chain about 10 H+ ions are pumped through the membrane, so for each NADH 2.5 ATP can be made (10/4=2.5).
  • FADH2 enters the chain a bit later (during complex 2), so they missed the first pump. FADH2 leads to 6 H+ being pumped though the membrane. So for each FADH2 about 1.5 ATP can be made (6/4=1.5).

This is why all that NADH and FADH2 pays off, this is where the majority of the eventual ATP comes from. It drives the proton (H+) pump that establishes the gradient for ATP synthase.

The yield from Glycolysis isn’t exact, it can be either three or five. This is because Glycolysis occurs in the cytosol and NADH can’t pass through the membrane into the mitochondria. Because it can’t deliver the electrons to complex 1 it needs an intermediary, a shuttle system.

  • Some cells hand it over to FADH2 inside the inner mitochondrial membrane, this results in 3 ATP (2 NADH -> 2FADH2 -> 12 H+ -> 3 ATP).
  • Other cells use NADH inside the inner mitochondrial membrane, resulting in 5 ATP (2 NADH -> 2NADH -> 20 H+ -> 5 ATP).

30-32 ATP is the upper bound of the estimate, in reality it is probably lower. Sometimes the intermediates are siphoned off to be used by other biological systems, ATP production is but one process of many.

This is the entire process where glucose is turned into energy that a cell can use. Oxygen is vital since it is the receiver for electrons used in the process. Without oxygen the process halts and you get no energy. The waste product is Carbon Dioxide and Water, where oxygen bonds to either a carbon or two hydrogen (can’t have them flying around on their own can we?)

So you breath to live, because you need the oxygen to turn glucose into energy. Without oxygen the production stops. Carbon Dioxide is the waste product of this process.

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Watch the video: You cant kill yourself by holding your breath! #WOW Facts (July 2022).


  1. Abelard

    It is exact

  2. Sewald

    Sorry, no to this paragraph .....

  3. Treasach

    This is the precious phrase

  4. Kigarg

    The sympathetic phrase

  5. Tavon

    It will be the last drop.

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