It is a blood clotting disorder that lacks factor VIII, one of the proteins involved in the process, found in the plasma of normal people.

Haemophiliacs have a tendency to have severe bleeding after minor injuries, such as minor injury or tooth extraction.

Treatment of haemophilia consists of the administration of purified factor VIII or blood derivatives in which it can be found (blood or plasma transfusions). Due to the frequent use of blood and blood products, hemophilia patients present a high incidence of AIDS and hepatitis B, diseases transmitted through these pathways.

Hemophilia affects about 300,000 people. It is conditioned by a recessive gene, represented by h, located on the X chromosome. The birth of hemophilic women is uncommon, since the woman, to present the disease, must be descended from a sick man (XhY) and a woman with a carrier. (XHXh) or hemophilic (XhXh).

As this type of crossover is extremely rare, it is believed that there would be virtually no hemophilic women. However, cases of haemophilia have been reported, contrary to the popular notion that these women would die from bleeding after their first menstruation (interruption of menstrual flow is due to contraction of endometrial blood vessels, not blood clotting) .