Causes and risk factors - Breast cancer in women

The causes of breast cancer are not fully understood, making it difficult to say why one woman may develop breast cancer and another may not.

There are risk factors known to affect your likelihood of developing breast cancer. Some of these you can't do anything about, but there are some you can change.


The risk of developing breast cancer increases with age. The condition is most common among women over 50 who have been through the menopause. About 8 out of 10 cases of breast cancer cases occur in women over 50.

All women who are 50 to 70 years of age should be screened for breast cancer every 3 years as part of the Breast Screening Programme - BreastCheck.

Previous breast cancer or lump

You have a higher risk of developing breast cancer again if you've previously had breast cancer.

The risk is also higher if you've had early non-invasive cancer cell changes in breast ducts. This could have been either in your other breast or in the same breast.

A benign breast lump doesn't mean you have breast cancer.

Certain changes in your breast tissue, such as cells growing abnormally in ducts (atypical ductal hyperplasia), or abnormal cells inside your breast lobules (lobular carcinoma in situ), can make getting breast cancer more likely.

Hormones and hormone medicine

Hormone replacement therapy (HRT)

Hormone replacement therapy (HRT) is associated with an increased risk of developing breast cancer. But the risk is very low.

Contraceptive pill

Women who use the contraceptive pill have a slightly increased risk of developing breast cancer. The risk starts to decrease once you stop taking the pill.

Your risk of breast cancer is back to normal 10 years after stopping.

Lifestyle factors


Alcohol is responsible for 1 in 8 breast cancers in Ireland

Your risk of developing breast cancer increases with the amount of alcohol you drink.

Alcohol can also increase the levels of some hormones, such as oestrogen, which can increase the risk of breast cancer.

Being overweight or obese

If you've experienced the menopause and are overweight or obese, you may be more at risk of developing breast cancer.

This is thought to be linked to the amount of oestrogen in your body. Being overweight or obese after the menopause causes more oestrogen to be produced.


Significant radiation exposure in the past may increase your risk of developing breast cancer. For example, some patients with Hodgkin's Lymphoma who received mantle radiation to the chest area.

Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 16 May 2019
Next review due: 16 May 2022