Hemophilia

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/14/2026Status: primary verified

What is hemophilia? Hemophilia is a rare bleeding disorder in which the blood does not clot properly. This can lead to problems with bleeding too much after an injury or surgery. You can also have sudden bleeding inside your body, such as in your joints, muscles, and organs. Your blood contains many proteins called clotting factors that can help form clots to stop bleeding. People with hemophilia have low levels of one of these factors, usually either factor VIII (8) or factor IX (9). How severe the hemophilia is depends on the amount of factor in the blood. The lower the amount of the factor, the more likely it is that bleeding could happen and might lead to serious health problems. What are the types of hemophilia? There are several different types of hemophilia. The most common are: Hemophilia A (classic hemophilia), which is caused by a lack or decrease of clotting factor VIII (8) Hemophilia B (Christmas disease), which is caused by a lack or decrease of clotting factor IX (9) What causes hemophilia? Most types of hemophilia are inherited. They are caused by change in one of the genes (also called a mutation) that provides instructions for making the clotting factor proteins. The change may mean that the clotting proteins don't work properly or that they are missing altogether. These genes are on the X chromosome. You may have one or two X chromosomes: People who are born male have one X chromosome (from the mother) and one Y chromosome (from the father). They can get hemophilia if their one X chromosome has the gene change. People who are born female have two X chromosomes, one from the father and one from the mother. They usually only get hemophilia if: Both X chromosomes have the gene change OR One X chromosome has the gene change and the other X chromosome is missing or inactive. People who are born female who have the gene change on one X chromosome are a "carrier" of hemophilia. Sometimes they may have some symptoms of hemophilia. They can pass the gene ch

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This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.