Acquired hemophilia is a bleeding disorder that prevents blood from clotting properly. Unlike congenital hemophilia, which is an inherited disorder, acquired hemophilia is not present at birth; it develops suddenly. When a person develops acquired hemophilia:

• Their body develops antibodies, or "inhibitors," that fight its own blood-clotting factors, mostly factor VIII
• Spontaneous, uncontrolled bleeding can occur
   

Acquired hemophilia occurs in people with no personal or family history of bleeding disorders. It is very rare, occurring in only about 1 to 1.5 per million people each year. It usually affects older people, as well as women who have recently given birth.

Acquired hemophilia can occur in association with other underlying conditions that involve the immune system, like cancer, other autoimmune diseases, or pregnancy. In about half of cases, there is no clear medical condition or reason that it happens.
 

Acquired hemophilia can happen without warning. The most common symptoms are:

• Bleeding into the skin (bruising)
• Bleeding into soft tissues
• Internal bleeding
• Excessive bleeding following childbirth or surgery

Acquired hemophilia is diagnosed with laboratory tests that measure clotting time of blood and factor VIII levels.