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 aren’t as many clotting factors as there should be in the blood. This means that someone with the condition bleeds for longer than usual.

The condition is passed to a child by one or both of their parents.

Read 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 mild, but people with severe haemophilia experience symptoms, which require ongoing care.

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 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’re caused by problems with different clotting factors and have slightly different treatments.

There’s also a rarer form of haemophilia called acquired haemophilia. This isn’t 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.

These pages are about haemophilia A and B.

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’s 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, some females who carry the haemophilia gene may also experience some bleeding problems, such as heavy periods. There’s also the 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. If there’s no family history, haemophilia tends to be diagnosed when symptoms appear in childhood.

Read more about diagnosing haemophilia.

Treating haemophilia

Although there’s no cure for haemophilia, treatment usually allows a person with the condition to 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.

Your local haemophilia centre

People with haemophilia should register at their local haemophilia centre, as this is a useful source of advice and support.

Find your local haemophilia centre.

Symptoms of haemophilia

The symptoms of haemophilia vary, depending on how severe the condition is, but the main sign is prolonged bleeding. The bleeding may occur spontaneously or after a medical procedure.

The severity of the condition is determined by the level of clotting factors in the blood:

  • mild haemophilia – where someone has between 5 and 50% of the normal amount of clotting factors
  • moderate haemophilia – where someone has between 1 and 5% of the normal amount of clotting factors
  • severe haemophilia – where someone has less than 1% of the normal amount of clotting factors

Most cases of haemophilia are severe.

Mild haemophilia

Children born with mild haemophilia may not have any symptoms for many years. The condition usually only becomes apparent after a significant wound, surgery, or a dental procedure such as having a tooth removed. These events could cause unusually prolonged bleeding.

Moderate haemophilia

As well as the above, children born with moderate haemophilia bruise easily. They may also have symptoms of internal bleeding around their joints, particularly if they have a knock or a fall that affects their joints. This is known as a joint bleed.

The symptoms usually begin with a tingling feeling of irritation and mild pain in the affected joint – most commonly the ankle joints, knee joints and elbow joints. Less commonly, the shoulder, wrist and hip joints can also be affected.

If a joint bleed isn’t treated, it can lead to:

  • more severe joint pain
  • stiffness
  • the site of the bleed becoming hot, swollen and tender

Severe haemophilia

The symptoms of severe haemophilia are similar to those of moderate haemophilia. However, joint bleeding is more frequent and severe.

Children with severe haemophilia have spontaneous bleeding. This means they start bleeding for no apparent reason. Spontaneous bleeding can take the form of nosebleeds, bleeding gums, joint bleeds and muscle bleeding.

Without treatment, people with severe haemophilia can develop:

  • joint deformity – which may require replacement surgery
  • soft tissue bleeding – which could lead to further complications
  • serious internal bleeding

When to seek emergency medical help

There’s a small risk of bleeding inside the skull, known as an intracranial haemorrhage. It’s estimated that 3% of people with moderate or severe haemophilia will have an intracranial haemorrhage. However, spontaneous bleeding inside the skull is uncommon and is usually only caused by a head injury.

Bleeding in the skull should be treated as a medical emergency.

The symptoms of an intracranial haemorrhage include:

  • severe headache
  • stiff neck
  • vomiting
  • a change in mental state – such as confusion
  • speaking difficulties – such as slurred speech
  • changes in vision – such as double vision
  • loss of co-ordination and balance
  • paralysis of some or all of the facial muscles

Call 999 for an ambulance if you suspect that someone is bleeding inside the skull.

Causes of haemophilia

Haemophilia is caused by an inherited genetic mutation, which mainly affects males.

A genetic mutation is a permanent alteration in the DNA sequence that makes up a gene. This means that some of the body’s processes won’t work in the normal way.

The type of mutation determines whether a family will experience mild, moderate or severe symptoms.


Chromosomes are strands of DNA. They contain a detailed set of instructions that control a wide range of factors, including how the body’s cells develop and the baby’s sex.

There are two types of sex chromosomes: the X chromosome and the Y chromosome. All humans have a pair of sex chromosomes. Men have an XY pair and women have an XX pair.

Boys inherit their X chromosome from their mother and their Y chromosome from their father. Girls inherit an X chromosome from each parent.

Haemophilia is inherited through a mutation in the X chromosome.

How the mutation is inherited

The chances of a child inheriting the haemophilia mutation depend on which of their parents has the mutated gene.

Only the mother is affected

If a woman with the mutated X chromosome and an unaffected man have a baby, there’s a:

  • one in four chance of having an unaffected baby boy
  • one in four chance of having a baby boy with haemophilia
  • one in four chance of having an unaffected baby girl
  • one in four chance of having a baby girl with one affected chromosome

In the last situation, the girl becomes a carrier of the mutated gene. This means she can pass it on to her children, but won’t usually have any severe symptoms of haemophilia herself. However, some female carriers sometimes have bleeding problems, such as heavy periods.

Only the father is affected

If a man with haemophilia has a son with an unaffected woman, there’s no chance the boy will get haemophilia. This is because he always inherits his X chromosome from his mother.

However, any daughters the man has will become carriers of the mutated haemophilia gene and may pass it on to their children. 

Both parents are affected

If a woman with the mutated chromosome and a man with haemophilia have a baby, there’s a:

  • one in four chance of having an unaffected baby boy
  • one in four chance of having a baby boy with haemophilia
  • one in four chance of having a baby girl who is a carrier of haemophilia
  • one in four chance of having a baby girl with haemophilia

This means it’s possible for a female to have haemophilia, although it’s very rare.

No family history

In some cases, a boy is born with haemophilia even though there’s no family history of the condition.

In such cases, it’s thought the mutation developed spontaneously in the boy’s mother, grandmother or great-grandmother, but until then a male member of the family had never inherited the mutated gene.

Although family history is a strong indicator, some studies have shown there’s no known family history of haemophilia in up to one-third of new cases.

How haemophilia affects the blood

Blood cells called platelets are very important for blood clotting. These cells have a sticky surface that allows them to clump together to stop the flow of blood.

Platelets also need clotting factors. These are proteins that form a “web” around the platelets, helping them to stay in place.

The mutated haemophilia gene means a child with the condition doesn’t have enough clotting factors in their blood.

Several different clotting factors are present in the blood. They are numbered using roman numerals. For example, in haemophilia A there’s not enough clotting factor VIII (8) in the blood. In haemophilia B, there’s not enough clotting factor IX (9) in the blood.

Diagnosing haemophilia

Haemophilia can be diagnosed before, during or after birth if there’s a family history of the condition. Several options are available to parents.

If there’s no family history of haemophilia, it’s usually only diagnosed when a child begins to walk or crawl. They may experience joint bleeds or easy bruising.

Mild haemophilia may only be discovered later, usually after an injury or a dental or surgical procedure.

Tests before pregnancy

Genetic testing and counselling are available to help determine the risk of passing the condition onto a child.

This may involve testing a sample of your tissue or blood to look for signs of the genetic mutation that causes haemophilia.

Tests during pregnancy

If you become pregnant and have a history of haemophilia in your family, tests for the haemophilia gene can be carried out. These include:

  • chorionic villus sampling (CVS) – a small sample of the placenta is removed from the womb and tested for the haemophilia gene, usually during weeks 11-14 of pregnancy
  • amniocentesis – a sample of amniotic fluid is taken for testing, usually during weeks 15-20 of pregnancy

There’s a small risk of these procedures causing problems such as miscarriage or premature labour, so you may want to discuss this with the doctor in charge of your care.

Tests after birth

If haemophilia is suspected after your child has been born, a blood test can usually confirm the diagnosis. Blood from the umbilical cord can be tested at birth if there’s a family history of haemophilia.

A blood test will also be able to identify whether your child has haemophilia A or B, and how severe it is.

Read more about how a blood test is performed.

Treating haemophilia

The recommended treatment plan for haemophilia depends on how severe the condition is.

There are two main approaches to treatment:

  • preventative treatment – where medication is used to prevent episodes of bleeding and subsequent joint and muscle damage
  • on-demand treatment – where medication is used in response to an episode of prolonged bleeding

Haemophilia is usually treated by a team at a specialist haemophilia hospital department.

Preventative treatment

Most cases of haemophilia are severe and require preventative treatment (prophylaxis). This involves regular injections of clotting factor medication.

When your child is young, you’ll be trained to give them the injections. They’ll be taught how to inject themselves when they’re older to help avoid regular hospital appointments.

In some cases, injections may be given into a device called an implantable port, which can be surgically placed under the skin. This port is connected to a blood vessel near the heart, meaning you don’t need to try to find a vein for every injection.

If you’re having preventative treatment, you’ll need regular follow-up appointments with your care team so your progress can be monitored.

Preventative treatment is usually continued until you’re fully grown. After this point, it may be possible to change to on-demand treatment, but you may be advised to switch back to preventative treatment if you experience any episodes of significant bleeding.

Haemophilia A

Preventative treatment for haemophilia A involves regular injections of a medication called octocog alfa. This is an engineered version of clotting factor VIII (8), the clotting factor that people with haemophilia A don’t have enough of. Injections every 48 hours are often recommended.

Side effects of octocog alfa are uncommon, but can include an itchy skin rash and redness and soreness at the site of the injection.

Haemophilia B

Preventative treatment for people with haemophilia B involves regular injections of a medication called nonacog alfa. This is an engineered version of clotting factor IX (9), which people with haemophilia B don’t have enough of. Injections twice a week are often recommended.

Side effects of nonacog alfa are uncommon, but include headaches, altered taste, nausea, and discomfort and swelling at the injection site.

On-demand treatment

In mild or moderate cases, treatment for haemophilia may only be necessary as an immediate response to bleeding.

Haemophilia A

People with haemophilia A can be treated on-demand with injections of octocog alfa or a medication called desmopressin.

Desmopressin is a synthetic hormone. Hormones are powerful chemicals that can have a wide range of effects on the body. Desmopressin works by stimulating the production of clotting factor VIII (8) and is usually given by injection.

Possible side effects of desmopressin include headache, stomach pain and nausea.

Haemophilia B

On-demand treatment for haemophilia usually involves injections of a medication called nonacog alfa.

For more information about these medications, read the page on haemophilia medicines information.

Living with haemophilia

With treatment, most people with haemophilia can live a normal life. However, there are some things you’ll need to be careful of.

For example, you should avoid contact sports such as rugby. You also need to be careful taking other medications, because some can interfere with your blood’s ability to clot. Common examples of these include aspirin and ibuprofen.

It’s important for people with haemophilia to maintain good oral hygiene and have regular trips to the dentist. This is to help avoid problems such as gum disease, which can cause bleeding. Most non-surgical dental treatment can be carried out in a general dental practice.

Your care team at the hospital can offer advice about surgical dental procedures, such as having a tooth removed, as well as further information and advice about living with haemophilia.

Complications of haemophilia

Haemophilia may lead to a number of problems that require further treatment.

Some people who take blood clotting factor medication may develop certain antibodies in their immune system, known as inhibitors. This happens if the immune system starts to treat clotting factors as foreign objects (like germs) and tries to block their effects.

Poorly-controlled haemophilia can also sometimes lead to joint damage, although this is becoming less common with modern treatments.


Inhibitors can make medication used to treat haemophilia less effective, which means it’s more difficult to prevent and control bleeding.

An estimated 20-30% of people who have treatment for severe haemophilia A develop inhibitors. This is much less likely to happen with mild or moderate haemophilia A. Inhibitors usually develop during the first year of treatment, but can occur at any time.

It’s rare for someone with haemophilia B to develop inhibitors, but if this does happen, the person could experience life-threatening anaphylaxis during treatment.

People receiving treatment for severe haemophilia A or B should be tested for inhibitors around every three to six months, eventually reducing this to a few times a year. Testing is also required if someone with haemophilia B experiences an allergic reaction to treatment.

People with mild or moderate haemophilia A usually only need a test after receiving intensive treatment, or once a year with normal treatment.

Inhibitors are often temporary, but there are ways of managing the problem if it’s persistent.

Immune tolerance induction for haemophilia A

People with severe haemophilia A who develop persistent inhibitors are usually advised to try a treatment programme called immune tolerance induction (ITI). This is carried out at specialist haemophilia care centres.

It involves receiving daily injections of octocog alfa. Over time, the immune system should begin to recognise the blood clotting factors and stop producing inhibitors.

ITI is carried out on a long-term basis, with most people needing a course of treatment that lasts between 6 and 24 months.

Mild or moderate haemophilia A is usually treated with bypass therapy (see below) or immunosuppressants (medications that reduce the activity of the immune system).

Immune tolerance induction for haemophilia B

ITI is sometimes used to treat persistent inhibitors in haemophilia B. It involves receiving daily injections of nonacog alfa. However, ITI is less successful at treating inhibitors in haemophilia B than it is in haemophilia A, and it carries a risk of anaphylaxis.

Managing a bleed with inhibitors

If someone with inhibitors has a bleed, a medication called a bypass agent must be used.

A bypass agent is a separate product that can be used to stop bleeding when inhibitors are still present. If ITI doesn’t work, you may need to use bypass agents for the rest of your life.

However, bypass agents can only be used as a response to prolonged bleeding, not as preventative treatment.

Joint damage

Successive joint bleeds can damage cartilage (the soft spongy tissue in joints that acts as a shock absorber) as well as the synovium (a thin layer of tissue that lines the inside of the joint).

The more damaged a joint is, the more vulnerable it is to internal bleeding. This means the joint becomes even more damaged and vulnerable to bleeding.

Joint damage is more common in older adults with severe haemophilia, because preventative treatments weren’t available in the past. It’s hoped that modern treatments mean children growing up with haemophilia today won’t have joint damage.

Surgery can be used to treat joint damage. If the synovium is damaged, it can be removed so new synovium can grow in its place. If a joint is seriously damaged, it may be necessary to replace the whole joint with an artificial one, such as a hip replacement or knee replacement.