Normal blood clotting depends on the interaction of many substances within the blood. Some of these are called clotting factors. If one of these clotting factors is not present in sufficient amounts, prolonged bleeding may occur. A person with hemophilia has less clotting factor than usual. A person with hemophilia does not bleed any faster than a normal person but the bleeding carries on for much longer.
Hemophilia affects males almost exclusively and is found in all populations.
It is passed on by women who usually have no bleeding problems. In about one-third of people with hemophilia, there is no family history of the disorder. In general, the more severe the hemophilia is, the earlier the signs of abnormal bruising or bleeding. Otherwise, babies seldom have problems until they begin to crawl and start to walk. The inevitable falls and bumps which occur in toddlers may cause skin bruises and bleeding from the lips and tongue.