The term "hemophilia" describes hemorrhagic, or bleeding, disorders. The most common of these disorders is caused by a deficiency of Protein in the blood known as 'blood-clotting factor'. There needs to be at least 30% of the clotting factor for the blood to clot normally. Less than 30% results in the blood being slow to clot, causing bleeding for a longer time than someone with a regular amount of clotting factor. Internal bleeding, usually into joints and muscles, is the most common form of bleeding sustained by those suffering from hemophilia. This can result from an incident such as a fall, or even spontaneously, with no apparent cause.