About Hemophilia
Hemophilia is an inherited bleeding disorder* caused by a shortage of “clotting
factors”—proteins in the blood that are needed to seal wounds and stop bleeding.
People with hemophilia are unable to form an effective clot to stop bleeding, such
as after an injury or during a dental procedure. Bleeding can also occur inside
a joint (hemarthrosis).
Get the basic facts about blood and blood clotting
Hemophilia A or "classical hemophilia" is the most common type of hemophilia, making
up about 80% of cases. It is caused by a deficiency of a specific clotting factor
known as factor VIII (FVIII). An insufficient amount of clotting factor IX results
in Hemophilia B, which accounts for most of the remaining 20% of hemophilia cases.
With few exceptions, hemophilia affects males; about 1 in 8,000 boys is born with
hemophilia. (While it is very rare, girls can be born with hemophilia if they have
a male relative with hemophilia.
See Rhonda’s story: Kristin’s surprise diagnosis)
A father with hemophilia cannot pass it to his sons. A son can only get the hemophilia
gene if his mother is a "carrier"—that is, she has the X chromosome on which the
gene for hemophilia resides. All women whose fathers have hemophilia are carriers.
Sons born to female carriers have a 50% chance of having hemophilia. Daughters born
to female carriers have a 50% chance of being carriers themselves, unless their
father has hemophilia. Learn more about the role of family history
*In rare cases, hemophilia can be acquired rather than inherited. Usually older adults are affected
and the cause is typically an autoimmune disorder, cancer, or reaction to certain drugs. Joint bleeds
in this kind of hemophilia are uncommon.
Learn about
Signs and Symptoms
of hemophilia.
