Hemophilia is a group of bleeding disorders in which the blood does not stick together (clot) properly. There are many types of hemophilia. Some occur when your body doesn't produce the proteins, called factors, that help blood clot. Other types result when blood factors do not work normally. Some forms of hemophilia are seen from birth, while others develop later because of an illness or treatment. Hemophilia causes easy, excessive bleeding. Someone with hemophilia may have frequent nosebleeds or abnormally heavy menstrual cycles (periods). Bleeding from hemophilia can be life threatening. Follow the links below to find WebMD's comprehensive coverage about how hemophilia develops, what the symptoms are, how to treat it, and much more.