What is haemophilia?

Haemophilia is an inherited bleeding disorder where the blood doesn't clot properly. It is caused when blood does not have enough clotting factor. A clotting factor factor is a protein in blood that controls bleeding.

  • Haemophilia A (also called classical haemophilia) is the most common form, and is caused by having low levels of factor VIII (8)
  • Haemophilia B (sometimes called Christmas Disease) is caused by having low levels of factor IX (9).

IHaemophilia is not contagious. It is a genetic condition and a person with haemophilia is born with it. It can be inherited and passed on from parent to child.

What causes haemophilia?

Everyone has the gene that makes clotting factor VIII (the factor 8 or F8 gene) and the gene that makes clotting factor IX (the factor 9 or F9 gene). These factors are needed for blood to clot. 

Haemophilia is caused by a change (mutation or alteration) in the F8 or F9 gene. The gene does not work as well as it should. As a result, the body does not make enough factor VIII (8) or factor IX (9) for blood to clot properly.

Who has haemophilia?

In Australia there are more than 3,100 people diagnosed with haemophilia. Both males and females with less than 40% of the normal level of clotting factor are now recognised as having haemophilia.

Most people who have been diagnosed with haemophilia are male. However, around 20-30% of females with the gene change have reduced factor levels and bleeding symptoms and may have haemophilia, usually mild haemophilia.  Severe haemophilia in females is very rare.

What happens when you have haemophilia?

A person with haemophilia does not bleed any faster than anyone else, but bleeding can continue for longer if it is not treated. This results in poor healing. Minor bruising or scratches on the skin are not usually a problem. 

For people with haemophilia, situations become more serious when there is internal or prolonged bleeding. If normal first aid does not stop the bleeding, without other treatment the bleeding can continue for days. Specialised treatment will be needed so blood can clot normally.

Bleeding is most commonly internal. The low levels of clotting factor produce a wide range of bleeding episodes, usually into the joints or muscles. These bleeding episodes, or 'bleeds', may occur spontaneously, without an obvious cause, or as a result of trauma or injury. Specialised treatment is needed and is often infused or injected into a vein. If internal bleeding is not stopped quickly with treatment, it will result in pain and swelling. Over a period of time bleeding into joints and muscles can cause permanent damage such as arthritis, chronic pain and joint damage requiring surgery.

Women and girls may have heavy and/or long menstrual periods. This is called heavy menstrual bleeding or sometimes abnormal uterine bleeding or menorrhagia. It can lead to anaemia (low levels of red blood cells or iron in the body).

Some women may also have heavy bleeding for a long time after childbirth.

It is important for people with haemophilia to involve their haemophilia treating team with any medical or dental procedures or surgery – anything larger than a blood test - to make sure it is managed safely.


Date last reviewed: 29 March 2023

How is haemophilia passed on?

Haemophilia is an inherited condition and occurs in families; however, in 1/3 of cases it appears in families with no previous history of the disorder. The genetic alteration causing haemophilia is passed down from parent to child through generations.

  • Men with haemophilia will pass the gene alteration on to their daughters but not their sons.
  • Women who carry the gene alteration can pass it on to their sons and daughters.
  • Sons with the gene alteration will have haemophilia.
  • Most women and girls who carry the gene alteration have normal clotting factor levels. Around 20-30% have reduced clotting factor levels. Sometimes their factor levels are low enought to be classified as having haemophilia, usually mild haemophilia. In a few very rare cases girls and women can have extremely low factor levels and have severe haemophilia.
Read more - can females have haemophilia?

The diagrams below may assist in understanding inheritance in haemophilia.
  • The red males have haemophilia
  • The red and blue females carry the gene alteration and some may also have haemophilia. They have one X chromosome with the gene alteration and one unaltered X chromosome.

Haemophilia Genetic Inheritance

Date last reviewed: May 2022

Where can I find more information?


For more information and frequently asked questions – click here - Haemophilia FAQ.

Download the HFA information booklets about haemophilia:

Haemophilia - [PDF, 1.7MB]

Living with mild haemophilia: a guide [PDF, 2.9MB]  

Click here for other HFA publications on haemophilia.


Australian Bleeding Disorders Registry (ABDR) Annual Report 2020-21. Canberra: National Blood Authority, 2021. [PDF, 1.7MB]

Australian Haemophilia Centre Directors' Organisation. Guidelines for the management of haemophilia in Australia. Canberra: National Blood Authority, 2016.

Hermans C, Kulkarni R. Women with bleeding disorders. Haemophilia. 2018;24(Suppl. 6):29-36.

World Federation of Hemophilia. Guidelines for the management of hemophilia. 3rd edn. Montreal: WFH, 2020.


This resource was reviewed by Leonie Mudge and Kate Lenthen from Australia/New Zealand Haemophilia Social Workers’ and Counsellors’ Group; Anne Jackson, Penny McCarthy, Megan Walsh and Claire Bell from Australian Haemophilia Nurses’ Group; Ian d’Young, Abi Polus and Wendy Poulsen from Australian and New Zealand Physiotherapy Haemophilia Group; Katherine Rose, Senior Genetic Counsellor, Monash Medical Centre, Victoria; Dr Chris Barnes, Dr Simon Brown, Dr Simon McRae and Dr John Rowell from Australian Haemophilia Centre Directors’ Organisation; and bleeding disorder community representatives from HFA Haemophilia and Women’s Project Consumer Review Groups.

Inheritance and information about women was reviewed by Dr Julie Curtin, Dr Jane Mason and Dr Stephanie P'ng from Australian Haemophilia Centre Directors’ Organisation in October 2018.

Date last reviewed: March 2023

Important Note: This information was developed by Haemophilia Foundation Australia for education and information purposes only and does not replace advice from a treating health professional. Always see your health care provider for assessment and advice about your individual health before taking action or relying on published information.
This information may be printed or photocopied for educational purposes.