Find out about how things we are exposed to can affect our risk of breast cancer.

Things we are exposed to in our lives, including from the surrounding environment, can affect our risk of breast cancer.

For more information on any of the below factors, download our pdf booklet Breast cancer risk: the facts.

Factors that can increase the risk of breast cancer developing

Ionising radiation

While exposure to high levels of ionising radiation increases the risk of many cancers, the risks associated with mammograms and other x-rays are very small. We can be exposed to ionising radiation through:

  • Natural sources including the ground, food and cosmic rays (which come from outer space and are found in the earth’s atmosphere).
  • An atomic bomb explosion or radiation accident.
  • Medical x-rays (including mammograms) and radiotherapy

Medical x-rays (including mammograms)

The amount of radiation you receive while undergoing a mammogram or other x-ray is very low. For example, the radiation exposure through a standard hospital x-ray is similar to the radiation you would be naturally exposed to over just a few days in your day-to-day life.

The health risks associated with this small exposure to ionising radiation are very small and are greatly outweighed by the benefits when x-rays are used appropriately.

If you have concerns about undergoing an x-ray or mammogram, we recommend that you talk this through with a healthcare professional. 

Radiotherapy treatment

Radiotherapy in the chest area can be used to treat Hodgkin’s lymphoma (also known as Hodgkin’s disease) and conditions such as some cancers and respiratory diseases. Women who received this type of radiotherapy before 2000 and when they were younger than their early 30s have an increased risk of developing breast cancer later in life. This is particularly the case for women who received radiotherapy during their developmental (teenage) years.

Since the early 2000s, the standard method of chest radiotherapy has changed and the risk of developing breast cancer later in life should be lower than with previous methods; however, more research is needed before we can be sure of the long-term effects of this more recent treatment.

The individual risk for any woman will depend on many factors, including the age when you were treated, the dose and type of radiotherapy you received, your current age and the amount of time that has gone by since you had your treatment.

If you have been treated with radiotherapy for Hodgkin’s lymphoma you should have been contacted by the lymphoma team or radiotherapy centre that treated you to discuss your breast cancer risk and options for breast cancer screening. If you have not been contacted but think you might be at risk, please contact the Lymphoma Association.

If you received radiotherapy treatment for other conditions before the early 2000s and are concerned that this may affect your risk of developing breast cancer, we suggest that you discuss this with your doctor. 

There is some scientific evidence to suggest the following factors may affect the chances of developing breast cancer

More research is needed before we can be sure whether or not they are definitely linked to the disease.

Shiftwork (working at night)

Women who regularly work shifts, particularly women who work night shifts, may have a slightly increased chance of developing breast cancer than women who do not. Further studies are needed before we can know for sure whether shiftwork affects breast cancer risk, why this might happen and whether there are steps that women performing shiftwork can take to reduce their risk.

Shiftwork can include working during the night and other work patterns, including long shifts (such as 12 hours), early or late shifts, or working for more than the usual number of days before having days off. There is more evidence for a possible link between night shiftwork and breast cancer than for other patterns of shiftwork.

Experts believe that shiftwork might increase the risk of breast cancer because women are exposed to light at night, but we are not sure why. Some studies in the laboratory have shown a lack of darkness may reduce the production of a hormone called melatonin, which might normally play a role in suppressing the growth of breast cancer. However, it has not yet been proven that reduced levels of melatonin in women working shifts are associated with breast cancer risk.

Another theory is that women working shifts have lower levels of vitamin D and that this affects their risk of breast cancer, but study results on this are not consistent.

Shiftwork might also lead to unhealthy behaviour that could independently increase the risk of cancer, such as being overweight and not being physically active. This makes the effects of shiftwork on breast cancer risk difficult to untangle from other lifestyle factors. 

Stress

We do not yet know whether stress increases the risk of breast cancer.

A possible link between stress and cancer is sometimes reported in the news. However, a number of studies have looked at the direct and indirect links between stress and breast cancer, and so far the overall evidence is not conclusive.

Stress is a highly subjective state so it is difficult to measure – how one person determines their stress levels can be very different from how another person does. Stress can also lead to unhealthy behaviour that could independently increase your risk of cancer, such as not being active, putting on weight and drinking alcohol. This makes the effects of stress on breast cancer risk difficult to pinpoint. 

Read a recent news story about stress and breast cancer risk.

Factors that are unlikely to affect breast cancer risk

The following factors are unlikely to affect breast cancer risk. For these factors, the overall scientific evidence suggests they aren’t linked to the disease. In some cases there simply isn’t any evidence of a link; in others, research has shown there’s no link.

Chemicals in the environment

Overall, there isn’t clear evidence that exposure to environmental chemicals increases breast cancer risk, based on the levels you would normally be exposed to in the UK. In general, levels of chemical pollutants in the environment are now declining, due to stronger regulations on their use.

There has been some concern that chemicals in the environment might have a role in increasing breast cancer risk, particularly endocrinedisrupting chemicals (EDCs). EDCs have a similar structure to the female hormone oestrogen. This means they may act like oestrogen or impact how oestrogen behaves. However, the hormone-like effects of these chemicals are thought to be far smaller than the effects of natural oestrogen.

Women who work in certain jobs, such as the manufacturing industry, can be exposed to higher levels of chemical pollutants, so they may be at higher risk of breast cancer. It is important to remember that in the UK most dangerous chemicals have been banned for decades, and employers are now legally required to limit exposure to chemicals that may cause cancer.

Lots of studies have looked at the link between chemicals in our environment and breast cancer. It takes many years for most breast cancers to develop and it is very difficult to work out what chemicals women with breast cancer have been exposed to over the 10, 20 or even 30 years before their breast cancer is detected. It is also hard to isolate the effects of individual chemicals on breast cancer risk when we are exposed to low levels of thousands of chemicals during our lifetime.

Breast cancer is likely to be caused by many factors, and we don’t know how the complex interactions between a person’s genes, lifestyle and surrounding environment contribute to breast cancer development. 

Non-ionising radiation

There is no good evidence to suggest that exposure to non-ionising radiation – such as the radiation generated by mobile phone masts, TVs, microwave ovens and computers – has any effect on your risk of developing breast cancer.

Exposure to a different type of radiation (called ‘ionising radiation’) increases the risk of many cancers, including breast cancer as discussed further up this page. 

More information

What should I do if I am worried about the risk factors mentioned here?

If you are worried about any of the breast cancer risk factors mentioned here you should discuss your concerns with your doctor.

Where can I get more information?

Breast Cancer Now has developed several free fact sheets that look in more detail at the effect of some factors on breast cancer risk. For an up-to-date list of the fact sheets available visit our publications information.

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Information last reviewed: July 2015

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