Risk factors for breast cancer

Breast cancer is likely to be caused by a combination of different risk factors. For example, getting older is one of the main risk factors for breast cancer.

What are risk factors?

The exact cause of breast cancer is unknown. But certain things can increase the chance of developing it. These are called risk factors. The risk factors for invasive breast cancer and ductal carcinoma in situ (DCIS) are similar.

Having 1 or more risk factors does not mean you will definitely get cancer. And if you do not have any risk factors, it does not mean you will not get breast cancer.

Breast cancer is likely to be caused by a combination of different risk factors, rather than just 1 risk factor.

If you are worried about breast cancer and would like to talk to someone, we're here. You can:


The biggest risk factor for breast cancer is age. About 8 in 10 women diagnosed (80%) are over the age of 50. Breast cancer is rare under 30.

If you have had breast cancer before

Your risk is increased if you have had breast cancer or ductal carcinoma in situ (DCIS) before. In this case, you will be monitored regularly. Any changes in the same breast or the other breast can be checked quickly.

Breast conditions

Having certain breast conditions can also increase the risk of breast cancer:

  • Lobular carcinoma in situ (LCIS)

    LCIS is when there are abnormal cell changes in the lining of the lobules (where milk is made).

  • Atypical ductal hyperplasia

    This is when there are slightly abnormal-looking cells in the milk ducts or lobules in a small area of the breast.

If you have 1 of these breast conditions, you are usually monitored regularly. This means any changes can be found early.

Dense breast tissue

Dense breast tissue is when the breast is mostly made of glandular and connective tissue with very little fatty tissue. If breast screening shows you have dense breast tissue, the risk of breast cancer is higher than if you have mainly fatty tissue.

Hormonal factors

The hormones oestrogen and progesterone can affect breast cancer risk. Factors that can increase your risk include:

  • taking hormone replacement therapy (HRT) for more than 5 years, especially if you are taking combined HRT (oestrogen and progesterone) – the risk reduces when you stop HRT
  • not having children
  • having your first child after the age of 30
  • not breastfeeding your children, or breastfeeding for less than 1 year in total
  • starting your periods early (under the age of 12) or having a late menopause (after the age of 55)
  • taking the contraceptive pill – the risk reduces if you stop taking it.

Family history and breast cancer risk

Most people who get breast cancer do not have a family history of it. If you have only 1 female relative diagnosed with breast cancer over the age of 40, your risk is likely to be similar to other women the same age as you.

But sometimes breast cancer can run in families. This is called inherited or hereditary breast cancer. The chance of it is higher when:

  • a number of family members have been diagnosed with breast cancer or related cancers, such as ovarian cancer
  • the family members are closely related
  • the family members were diagnosed at a younger age
  • a man in the family has been diagnosed with breast cancer.

Fewer than 1 in 10 breast cancers (10%) are thought to be inherited. They are caused by a change (mutation) in a gene in the family. In inherited breast cancer, the 2 genes usually found to have a change are:

If you have triple negative breast cancer, you may be offered genetic testing. This is offered even if you do not have a family history of breast cancer. Most breast cancers caused by a change in the BRCA1 gene are triple negative. Your cancer doctor or breast care nurse can explain more about this to you.

If you are worried about breast cancer in your family, talk to your GP or a breast specialist. They can refer you to a family history clinic or a genetics clinic.

Lifestyle factors

Certain lifestyle factors may increase breast cancer risk.

  • Being overweight

    The risk of breast cancer is higher if you are overweight, particularly after the menopause. This is because being overweight may change hormone levels in the body. Keeping to a healthy weight can help reduce the risk of breast cancer.

  • Alcohol

    Regularly drinking alcohol increases the risk of breast cancer. But the risk is lower for women who drink within the recommended guidelines.

  • Smoking

    Smoking can slightly increase the risk of breast cancer. This seems to be linked with starting smoking at a young age and smoking for a long time. We have information about stopping smoking.

We have more information about what you can do to help reduce certain risk factors.

Radiotherapy to the chest at a young age

Radiotherapy to the chest before the age of 30 increases the risk of breast cancer. You may have radiotherapy to the chest to treat Hodgkin lymphoma. In this situation, you will usually be offered breast screening.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Dr Rebecca Roylance, Consultant Medical Oncologist and Professor Mike Dixon, Professor of Surgery and Consultant Breast Surgeon.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 October 2023
Next review: 01 October 2026
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.