Haemophilia is an inherited condition that affects the blood's ability to clot.
Normally, when you cut yourself substances in the blood known as clotting factors combine with blood cells called platelets to make the blood sticky. This makes the bleeding stop eventually.
However, in haemophilia there are not as many clotting factors as there should be in the blood. This means someone with the condition will bleed for longer than usual.
The condition is passed to a child by one or both of their parents.
Find out more about the causes of haemophilia.
How it affects you
The symptoms of haemophilia can be mild to severe depending on the level of clotting factors you have. Most cases are classified as severe.
People with severe haemophilia often experience internal bleeding. This usually occurs around the joints and muscles, causing pain and stiffness. It can also lead to joint damage over time.
Read more about the symptoms of haemophilia and the complications of haemophilia.
Types of haemophilia
The two most common types of haemophilia are haemophilia A and haemophilia B, although haemophilia A accounts for the majority of cases.
Both types have the same symptoms, but they are caused by problems with different clotting factors and have slightly different treatments.
There is also a rarer form of haemophilia called acquired haemophilia. This is not an inherited condition but is caused by the immune system (the body's natural defence against infection and illness) attacking the clotting factors in the blood.
This section is about haemophilia A and B. See the Haemophilia Society website for more information about acquired haemophilia.
Who is affected?
There are about 6,000 people with haemophilia in the UK. Most of these are males because of the way the condition is inherited.
Worldwide, it is estimated that one boy in every 5,000 will be born with haemophilia A and one boy in every 30,000 will be born with haemophilia B.
However, females who carry the haemophilia gene may also experience some bleeding problems, such as heavy periods. There is also a chance that a girl could be born with haemophilia if both parents have the haemophilia gene.
If you have a family history of haemophilia, you can have tests before, during and after pregnancy to determine if your child has the condition.
Read more about diagnosing haemophilia.
There is no cure for haemophilia. However, with treatment a person with the condition can usually enjoy a good quality of life.
In recent decades genetically engineered clotting factor medications have been developed to prevent and treat prolonged bleeding.
These medications are given as an injection, the timing of which depends on how severe the condition is. Injections are usually only given in milder cases in response to prolonged bleeding, whereas more severe cases are treated with regular injections to prevent bleeding.
Read more about treating haemophilia.