Risk factors

Breast cancer is now the most common cancer in the UK. It is by far the most common cancer in women.

1 in 7 women in the UK develop breast cancer during their lifetime. 

In 2017 in the UK there were around 54,700 women and 390 men diagnosed with breast cancer. 

Anything that increases the risk of getting a disease is called a risk factor.

Having one or more of the following risk factors doesn’t mean that you will definitely get breast cancer. Many people who have these factors never get it and some people with no risk factors develop it.

Women who are overweight after their menopause have a higher risk of breast cancer than women who are not overweight. Men also have an increased risk of breast cancer if they are overweight or obese. For both men and women, the risk increases as more weight is gained. 

Body mass index (BMI) is a measure that uses your height and weight to work out whether you are a healthy weight. For most adults, an ideal (BMI) is between 18.5 to 24.9. Being overweight means having a BMI of between 25 and 30. Obesity means being very overweight with a BMI of 30 or higher.

Try to keep a healthy weight by being physically active and eating a healthy, balanced diet.

Drinking alcohol increases the risk of breast cancer in women. The risk increases with each extra unit of alcohol per day. The number of units in a drink depends on the size of the drink, and the volume of alcohol.

The latest UK government guidelines advise drinking no more than 14 units of alcohol a week.

There is a very small increased risk of breast cancer when you take the contraceptive pill. This increase in risk goes back to normal 10 years after you stop taking it.

Remember that breast cancer is rare in young women. Most women who take the pill are in their late teens, twenties and early thirties. So a small increase in this risk during the time women take the pill means very few extra cases of breast cancer.

Many women take hormone replacement therapy (HRT) to reduce menopausal symptoms. There are 2 main types of HRT: 

  • combined HRT (oestrogen and progesterone) 
  • oestrogen only HRT

The risk of breast cancer increases for postmenopausal women using any type of HRT. But it is biggest for those using combined HRT.  

Risk is also higher in those who use HRT for more than 5 years. And for these women, the risk remains increased for at least 10 years after they stop using it.

HRT can have some health benefits. So, if you are worried about taking it, talk to your doctor about the benefits and risks for your individual situation.

There is a small increased risk of breast cancer if you’re inactive, this means doing less than 150 minutes of moderate exercise a week. Daily physical activity is recommended to gain health benefits. It can be easier than you think to increase your activity even if you don't do much at the moment. 

Activity doesn’t just mean sport and exercise. Anything that makes you a bit warmer and slightly out of breath counts as moderate activity. 

Risks that you can't change

Most breast cancers occur in women over 50 and it is less common in women under 40.

Some people have a higher risk of developing breast cancer than the general population because other members of their family have had particular cancers. This is called a family history of cancer.

Having a mother, sister or daughter diagnosed with breast cancer increases the risk of breast cancer. This risk is higher when more close relatives have breast cancer, or if a relative developed breast cancer under the age of 50. But most women who have a close relative with breast cancer will never develop it.

Some people have an increased risk of breast cancer because they have an inherited gene fault. We know about several gene faults that can increase breast cancer risk and there are tests for some of them. Having one of these faulty genes means that you are more likely to get breast cancer than someone who doesn’t. But it is not a certainty. 

Two of these faulty genes are known as BRCA1 and BRCA2. These are not common. Only about 2 out of every hundred (about 2%) of breast cancers are related to a change in the BRCA1 or BRCA2 genes.

Ionising radiation includes tests such as x-rays and CT scans and treatment such as radiotherapy.

X-rays and mammograms

Exposure to radiation is known to increase the risk of many types of cancer. Most of us are never exposed to enough radiation to make much difference to our risk.

Nowadays, doctors keep medical exposure to radiation as low as possible. They don't do x-rays or CT scans unless they really need to. And the amount of radiation used is very small.

Many women worry about having mammograms as part of breast screening because it exposes them to x-rays. But the amount of radiation you have with a mammogram is very small.


Radiotherapy treatment for breast cancer increases the risk of getting breast cancer in the other breast by a small amount. But this small risk is balanced by the need to treat the original breast cancer.

If you had radiotherapy to your chest area to treat another type of cancer your risk of developing breast cancer is higher than someone who hasn't had radiotherapy. This is especially so for women who have had chest radiotherapy for Hodgkin lymphoma in the past.

If you need radiotherapy for Hodgkin lymphoma or any other type of cancer your doctors should tell you about this risk. They will offer you breast screening if it is appropriate. Talk to your doctor if you are unsure if you should have screening. 

It is important to remember that second cancers are usually found early when they can be successfully treated. Also, radiotherapy treatments are now more focused than in the past.

Women with diabetes have a small increase in their risk of breast cancer, although we are not sure why.

Breast cancer risk is higher in women with the most dense breast tissue compared to less dense tissue. Women with dense breast tissue have less fat and more breast cells and connective tissue in their breasts.

Our genetic make up affects breast density.

Benign breast disease means there is a change in the breast that is not cancer.

There are 3 types:

  • non proliferative
  • proliferative without atypia
  • proliferative with atypia (atypical hyperplasia)

Non proliferative

Breast disease that is not growing and where the cells are not dividing is called non proliferative. It doesn’t usually increase the risk of breast cancer. But if you have a strong family history of breast cancer you might have a small increased risk.

Proliferative without atypia 

Breast lumps with an overgrowth of cells (proliferation) but without abnormal (atypical) cells increase the risk of breast cancer compared to the average risk.

Atypical hyperplasia

This means the cells are not cancer but are growing abnormally. Atypical hyperplasia can increase your risk of breast cancer.

It is not common, if you haven't been told that your breast lump showed these changes, it probably didn't. But if you are worried, you can ask your doctor about it.

You should always get breast lumps checked out straight away to make sure they are not cancer.

DCIS and LCIS are changes within the breast tissue that might develop into breast cancer in some women. DCIS stands for ductal carcinoma in situ. LCIS stands for lobular carcinoma in situ.

Women with a diagnosis of DCIS or LCIS have double the usual risk of invasive breast cancer in the same or other breast. But it is important to remember that most women with LCIS or DCIS will not develop invasive cancer.

You have an increased risk of breast cancer if your periods started early (before the age of 12). Having a late menopause (after the age of 55) can also increase your breast cancer risk. 

This increased risk is likely due to longer exposure to the hormone oestrogen.

Levels of sex hormones can increase breast cancer risk. These hormones include:

  • oestrogen
  • progesterone
  • testosterone

The male hormone, testosterone, can affect the risk of breast cancer. Women have small amounts of the male hormone testosterone in their bodies.

After the menopause, women with higher levels of oestrogen and testosterone in their blood may have a higher risk of breast cancer.

Women with higher levels of testosterone in their blood before menopause have a higher risk of breast cancer.

There is an increased risk of breast cancer in women with higher levels of a hormone called insulin like growth factor 1 (IGF-1). It is not clear what controls levels of IGF-1 in the bloodstream. It is probably related to our genes, body weight, and how much exercise we do.

A large report found that the risk of breast cancer is higher in white women than any other ethnic group. This is at least partly due to lifestyle factors.

Having had breast cancer increases your risk of getting another breast cancer. It might occur in the same breast or in the other breast.

Your specialist will keep a close eye on you with regular check ups. So, a new cancer should be picked up early.  

Having other types of cancer can also increase your risk.

People who had radiotherapy to the chest for Hodgkin lymphoma when they were young have a higher breast cancer risk.

Breast cancer risk is also higher in people who have had any of the following:

  • melanoma skin cancer
  • lung cancer
  • bowel cancer
  • womb cancer
  • a type of leukaemia called chronic lymphocytic leukaemia

Women who are taller than average have a slightly increased risk of breast cancer after the menopause.

It is not clear why but it could be due to different hormone levels in taller women.

Whether you can have children or when you have them may not be something you can control. Women who have children have a slightly lower risk of breast cancer than women who don't have children. The risk reduces further the more children you have.

Your age when you have your first child also has an effect. The younger you are when you have your first child, the lower your risk.

Where there isn't clear evidence

Some factors might increase the risk of breast cancer but there is not enough evidence to be sure.

There has been a lot of research into whether diet increases the risk of breast cancer. So far most findings have been inconclusive and inconsistent.

Research has looked at a number of foods including:

  • fat
  • dairy foods
  • fibre
  • fruit
  • soya (soy)

Researching diet and breast cancer is very difficult because we all eat such a range of different foods in such differing amounts. A large study called EPIC (the European Prospective Investigation into Cancer) is looking at the links between lifestyle and cancer. It involves around 520,000 people in 10 European countries.

Eating a healthy, balanced diet can help you keep a healthy body weight. There is evidence that being overweight or obese after the menopause, can increase your risk of breast cancer.

Smoking tobacco might increase your risk of getting breast cancer. It is never too late to stop smoking but the sooner you stop the better.

Factors that reduce the risk of breast cancer

Some factors can reduce the risk of breast cancer

Cancer controversies

Stories about potential causes of breast cancer 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.

More information about breast cancer risks and causes

We have very detailed information for health professionals about breast cancer risks and causes.

This page is due for review. We will update this as soon as possible.

  • Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence
    Collaborative Group on Hormonal Factors in Breast Cancer
    The Lancet, 2019. Volume 394, Issue 10204, Pages 1159-1169

  • Hormonal contraception and breast cancer, what more do we need to know?

    J Marsden

    Sage Journals, 2017. Volume 23, Issue 3, pages 116-127

  • Diabetes, Obesity, and Breast Cancer

    C Kang, and others 

    Endocrinology, 2018. Volume 159, Issue 11, Pages 801–3812

  • Familial breast cancer: classification, care and managing breast cancer and related risks in people with a family history of breast cancer
    National Institute for Health and Care Excellence (NICE), 2013. Updated November 2019

  • Risk-Based Breast Cancer Screening: Implications of Breast Density

    C Lee and others

    Medical clinics of North America, 2017. Volume 101, Issue 4, Pages 725–741

  • 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 patientinformation@cancer.org.uk with details of the particular risk or cause you are interested in.

Last reviewed: 
21 Jan 2020
Next review due: 
21 Jan 2023

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