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Risks and causes

Your risk of developing cancer depends on many things including environmental, lifestyle and genetic factors. 

Anything that can increase or decrease your risk of cancer is called a risk factor. 

We don't know what causes most cases of acute lymphoblastic leukaemia (ALL). But there are some factors that may increase your risk of developing it.  

Having one or more risk factors doesn't mean that you will definitely get leukaemia. 

Risk factors for ALL include:

We’ve known for a long time that exposure to very high levels of ionising radiation increases acute leukaemia risk. For example, people exposed to the atomic bomb explosions in Japan at the end of World War 2 had higher rates of leukaemia.

A 20 year study has followed up workers who helped clean up after the Chernobyl nuclear power plant accident in 1986. It shows that even at low doses of ionising radiation there is an increased risk of all types of leukaemia.

Some people worry that childhood x-rays cause leukaemia in children. A large study found there is very little evidence of any increase in risk, except in a type of leukaemia that is rare in children, called pre B cell ALL (or pre B ALL). But the researchers say that even this could be a chance finding and not a real risk increase.

There is some evidence that x-rays during pregnancy could increase the risk of childhood leukaemia. So doctors avoid x-rays for pregnant women whenever possible.

CT scans and radiotherapy treatment also use ionising radiation. Research has also suggested that in children this could increase the risk of developing leukaemia in the future. However, it's important to note that doctors make sure the benefits of having the test or treatment outweighs the risks.   

Exposure to a chemical called benzene at work can increase the risk of developing ALL. Exposure to benzene may occur in petrol, chemical, pharmaceutical and rubber industries. Benzene is also used in shoe production and the printing industry. The higher the level of exposure over many years, the greater the risk. There is benzene in traffic pollution but the levels are likely to be too low to increase leukaemia risk.

Cigarette smoke contains lots of harmful chemicals (including benzene) that can cause at least 15 types of cancer in adults, including leukaemia.

Studies have also shown that parents who smoke may increase the risk of leukaemia in their children. This could include smoking by the father in the time before conception.

Certain rare, inherited conditions can increase the risk of acute leukaemia, including:

  • Down’s syndrome
  • Fanconi anaemia
  • ataxia telangiectasia
  • Bloom syndrome

People who have had certain chemotherapy drugs in the past have a slightly increased risk of developing leukaemia some years later. The risk depends on how much treatment you had. Some of the drugs include:

  • etoposide with cisplatin and bleomycin
  • thiotepa
  • busulfan
  • chlorambucil
  • melphalan

It's important to remember that this risk is still very small compared to the risk to your health if the cancer had not been treated.

We know that a virus called HTLV-1 (human T cell leukaemia virus) increases the risk of developing a rare type of adult T cell leukaemia.

HTLV-1 is a very rare virus in the UK, and most people who carry the virus do not develop cancer because of it. 

The virus can spread through blood (sharing needles), bodily fluids (unprotected sex) and from mother to baby (mainly through breastfeeding). 

Exposure to infection in childhood

Children may have a slightly increased risk of ALL if they do not come across common infections from birth, but are exposed to them later in life. 

Researchers continue to look into this along with other factors like genetics. 

You may read in the press from time to time that some people are concerned about power lines and risk of cancer. Power lines produce high levels of 'low frequency electromagnetic radiation' (EMR).

Although some studies seem to suggest that exposure to very high levels of EMR could increase childhood leukaemia risk, the findings are not very clear. We don’t really know if the childhood leukaemia in these studies was actually caused by low frequency EMR. It could be due to some other common factors, or even chance. 

In 2018, a large international study of overhead power lines and child leukaemia found no association. This was true even for children living within 50 metres of a power line. 

Studies have suggested a slightly higher risk of childhood ALL after high exposure to house painting. But the findings are not conclusive and we need more studies to back up this finding.

An overview study (combined analysis) looked at published research into people with HIV or AIDS, or people treated with medicines that lower immunity after an organ transplant. The researchers found that these people have a risk of leukaemia that is double or triple that of people without these factors.

Other possible causes

Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.

Last reviewed: 
24 Apr 2019
  • List of Classifications by cancer sites with sufficient or limited evidence in humans, Volumes 1 to 123*
    The Internal Agency for Research on Cancer (IARC).
    Accessed April 2018

  • Exposure to benzene at work and the risk of leukemia: a systematic review and meta-analysis
    A Khalade and others
    Environmental Health, 2010. Volume 9, Issue 31

  • Ionising radiation and risk of death from leukaemia and lymphoma in radiation-monitored workers (INWORKERS): an international cohort study
    K Leuraud and others
    Lancet Haematology, 2015. Volume 2, Pages e276 – e 281

  • Parental occupational paint exposure and risk of childhood leukaemia in the off spring: Findings from the Childhood Leukemia International Consortium
    H D Bailey and others
    Cancer Causes Control, 2014. Volume 25, Issue 10, Pages 1351 – 1367

  • The Exceptional Oncogenicity of HTLV-1
    Y Tagaya and R C Gallo
    Frontiers in Microbiology, 2017. Volume 8, Page 1425

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact with details of the particular risk or cause you are interested in.