In fact, external bleeding is seldom a serious problem for hemophiliacs. They may bleed somewhat longer than other people, but minor bleeding episodes can generally be controlled by ordinary first-aid measures. Blood that leaks into the knee joint, a common site of internal bleeding, can cause painful swelling. Repeated bleeding eventually destroys cartilage that enables the knee to work smoothly and easily. The joint becomes permanently stiff and painful, the result of hemophilic arthritis.
Patients can also bleed into muscle and other soft tissue.
If unchecked internal bleeding involves air passages or the brain or other vital organs, the patient's life is in grave danger. The cause of hemophilia and other blood-clotting disorders is well understood. In hemophilia, the problem lies with one of the factors responsible for forming blood clots. Probably the most common hereditary bleeding disorder is von Willebrand disease, a somewhat milder illness caused by failure of the factor that makes platelets clump together to plug damaged blood vessels. An illness like the one we now know as hemophilia was recognized in antiquity, and in the fifth century A.D. Jewish rabbis decreed that newborn males were exempt from the requirement to be circumcised if they had brothers or uncles who had bled to death following circumcision.