Hemophilia is rare, x-linked bleeding disorder caused by the deficiency of a specific blood clotting protein (factor VIII or IX). This results in delayed or prolonged bleeding time. Depending on the severity of the disease, prolonged bleeding can occur spontaneously or following trauma or surgery. People with hemophilia A have low levels of factor VIII, while people with hemophilia B have low levels of factor IX. The lower the level of clotting factor in the bloodstream, the more at risk a person is for bleeding. Head and organ injuries pose the greatest danger, while repeated joint and muscle bleeds can lead to long-term joint and tissue damage.