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Factors Linked to Breast Cancer Risk

Some factors are linked to a small increased (or decreased) risk of breast cancer and others are linked to a larger increased (or decreased) risk.

Understanding which factors are linked to breast cancer risk can help you work with your health care provider to address any concerns you have and develop a breast cancer screening plan that’s right for you.

Our Breast Cancer Risk Factors Table compares risk factors by level of risk and strength of evidence. 

Factors that affect breast cancer risk are listed alphabetically below. Click on the topics below to learn more.

Age is a risk factor for breast cancer in both women and men. The older a person is, the more likely they are to get breast cancer.

Learn more about age and breast cancer risk.  

Both the age when a woman gives birth to her first child and the number of childbirths a woman has are linked to the risk of breast cancer.

Women who give birth to their first child at age 35 or younger tend to have a lower risk of breast cancer than women who give birth for the first time at an older age and women who never give birth [10-14].

In general, the more times women have given birth, the lower their risk of breast cancer tends to be [10-14,17].

Learn more about age at first childbirth, number of childbirths and breast cancer risk.

Starting menstrual periods at a young age is linked to a small increase in breast cancer risk [13,17,19-21].

For example, women who began their periods before age 11 have about a 15% to 20% higher risk of breast cancer compared to those who began their periods at age 15 or older [20].

Learn more about age at first period and breast cancer risk.

Going through menopause at a later age is linked to an increased risk of breast cancer [12-13,17,19,23].

For example, women who go through menopause after age 55 have about a 40% higher risk of breast cancer than women who do so at age 45 or younger [12].

Learn more about age at menopause and breast cancer risk.

Drinking alcohol is linked to an increased risk of breast cancer [24].

For example, women who have 2-3 alcoholic drinks per day have about a 20% higher risk of breast cancer than women who don’t drink alcohol [24].

Learn more about alcohol and breast cancer risk.

Learn about alcohol and breast cancer survival.

Anti-Müllerian hormone (AMH) is produced in the ovaries. It’s important in the development of reproductive organs.

Women with higher blood levels of AMH may have a higher risk of breast cancer compared to women of the same age with lower levels of AMH [28-31].

Learn more about AMH hormone levels and breast cancer risk.

BRCA1 and BRCA2 (BRCA1/2) inherited gene mutations are more common in Ashkenazi Jews (Jewish people of Eastern European descent) than in other people [38-39]. These gene mutations increase the risk of breast cancer and other cancers [33-39].

Learn more about Ashkenazi Jewish heritage, BRCA1/2 inherited gene mutations and breast cancer risk.

Being born female is the main risk factor for breast cancer. Although men can get breast cancer, it’s about 100 times more common in women [41].

Learn more about being born female and breast cancer risk.

Learn more about breast cancer in men.

Current or recent use of birth control pills is linked to a slight increase in breast cancer risk [13,42-45].

For example, women who take birth control pills (or recently used them) have a 20%-30% higher risk of breast cancer than women who’ve never taken the pill [42,44-45].

Learn more about birth control pills and breast cancer risk.

Learn about other types of contraceptives that contain hormones (including Depo Provera, the birth control patch and the vaginal ring) and breast cancer risk.

Women with a higher birthweight (a woman’s weight when she was born) have a higher risk of breast cancer, especially before menopause, compared to women with a lower birthweight [55-61].

Learn more about birthweight and breast cancer risk.

Learn more about early life exposures and breast cancer risk. 

Androgens (such as testosterone) are natural hormones. They are important in sexual development.

Women with higher levels of androgens in their blood have a higher risk of breast cancer compared to women with lower blood androgen levels [67-70].

Learn more about blood androgen levels and breast cancer risk.

Estrogens are natural hormones. They are important in sexual development and other body functions.

Women with higher blood levels of estrogen after menopause have a higher risk of breast cancer compared to women with lower blood levels of estrogen after menopause [22].

Researchers are studying a possible link to breast cancer before menopause.

Learn more about blood estrogen levels and breast cancer risk.

Being overweight differs in the way it’s linked to breast cancer risk before and after menopause.

  • Before menopause, women who are overweight or obese have a modestly decreased risk of breast cancer [74-78].
  • After menopause, women who are overweight or obese have an increased risk of breast cancer [75,76-79].

Gaining weight in adulthood is linked to an increased risk of breast cancer after menopause [88-92]. Gaining weight in adulthood and a possible link to the risk of breast cancer before menopause is under study [78,91,96,638-639].

Learn more about body weight, weight gain and breast cancer risk.

Learn about body weight and breast cancer survival. 

Women with high bone density have about a 60% to 80% higher risk of breast cancer compared to women with low bone density [110].

Learn more about bone density and breast cancer risk. 

Breast density is a measure used to describe the proportion of the different tissues that make up a woman’s breasts. It compares the area of breast and connective tissue seen on a mammogram to the area of fat.

Women with very dense breasts are 4-5 times more likely to get breast cancer than women with fatty breasts [112-113].

Learn more about breast density and breast cancer risk.

Women who breastfeed have a lower risk of breast cancer, especially before menopause, than women who don’t breastfeed [14,17,120-122].

Learn more about breastfeeding and breast cancer risk.

Women who get regular exercise (physical activity) have about a 10% to 20% lower risk of breast cancer than women who are not active [130-137].

Learn more about exercise and breast cancer risk.

Learn about exercise and breast cancer survival.

People with a family history of breast, ovarian or prostate cancer have an increased risk of breast cancer [38]. The increased risk is likely due to genetic factors but may also be due to shared lifestyle factors or other family traits.

Learn more about a family history of breast, ovarian or prostate cancer and breast cancer risk.

Learn more about inherited gene mutations and breast cancer risk.  

Fruits and vegetables

Eating fruits may be linked to a lower breast cancer risk [168]. Eating vegetables may be linked to a lower risk of some breast cancers [165-168].

Carotenoids

Carotenoids are natural orange-red food pigments found in fruits and vegetables such as melons, carrots and sweet potatoes. Beta-carotene is an example of a carotenoid.

Women with higher blood levels of carotenoids have a decreased risk of breast cancer compared to women with lower levels of carotenoids [172].

Learn more about fruits, vegetables, carotenoids and breast cancer risk.  

Taller women have a higher risk of breast cancer than shorter women [13,97,179-186].

Learn more about height and breast cancer risk. 

Benign breast conditions (also called benign breast diseases) are non-cancerous breast disorders.

Some benign breast conditions are linked to an increased risk of breast cancer and others are not. For example, women with hyperplasia have an increased risk of breast cancer [188-191].

Learn more about hyperplasia and other benign breast conditions and breast cancer risk.

Learn more about different types of benign breast conditions.  

Insulin-like growth factor 1 (IGF-1) is a natural hormone that plays a role in growth and development.

Women with higher levels of IGF-1 in their blood may have a higher risk of breast cancer than women with lower levels of IGF-1 [248-251].

Learn more about IGF-1 and breast cancer risk.

Some inherited gene mutations have been linked to breast cancer. These include mutations in the following genes (in alphabetical order):

  • ATM
  • BARD1
  • BRCA1
  • BRCA2
  • CDH1
  • CHEK2
  • NF1
  • PALB2
  • PTEN
  • RAD51C
  • RAD51D
  • STK11
  • TP53

Other genes are under study and may also play a role in breast cancer.

Learn more about inherited gene mutations and breast cancer risk.

Find information for women who have a BRCA1 or BRCA2 inherited gene mutation.

Find information for men who have a BRCA1 or BRCA2 inherited gene mutation.

Women who routinely work night shifts for many years have a small increased risk of breast cancer [252-255]. One possible reason for the increased risk among these workers is their exposure to light at night.

More research is needed to understand which aspects of shift work may be related to breast cancer risk.

Learn more about light at night, shift work and breast cancer risk. 

When abnormal cells grow inside the lobules of the breast, but have not spread to nearby tissue or beyond, the condition is called lobular carcinoma in situ (LCIS).

Although the term LCIS includes the word “carcinoma,” LCIS is not invasive breast cancer. However, LCIS increases the risk of invasive breast cancer.

Compared to women without LCIS, those with LCIS are 7-11 times more likely to develop invasive breast cancer [258-259].

Learn more about LCIS and breast cancer risk. 

Menopausal hormone therapy (MHT) is FDA-approved for the short-term relief of menopausal symptoms [265]. MHT is also called postmenopausal hormone therapy and hormone replacement therapy (HRT).

The main types of MHT pills are:

  • Estrogen plus progestin
  • Estrogen alone

Women who use estrogen plus progestin MHT have an increased risk of breast cancer [266-271].

Some studies have shown women who use estrogen alone may also have an increased risk of breast cancer [267-269]. However, one large study found these women had a decreased risk [277].

MHT is not usually given to women who’ve been treated for breast cancer because it may be linked to an increased risk of recurrence [279-282].

Learn more about MHT and breast cancer risk. 

Learn more about MHT and breast cancer recurrence.  

Learn about other ways to manage menopausal symptoms.

Women who’ve had breast cancer in the past have a higher risk of getting a new breast cancer compared to women who’ve never had breast cancer [283-284].

Ductal carcinoma in situ (DCIS) is a non-invasive breast cancer. After treatment for DCIS, women still have a small risk of a DCIS recurrence or invasive breast cancer [214,292-297].

A personal history of Hodgkin lymphoma (Hodgkin’s disease), ovarian cancer or certain other cancers also may be linked to an increased risk of breast cancer [38-39,298-303].

Learn more about a personal history of breast cancer or other cancers and breast cancer risk.  

Prolactin is a natural hormone that plays a role in breast growth and the production of milk during breastfeeding.

Women with higher blood levels of prolactin have a slightly higher risk of breast cancer than women with lower levels [305-306].

Learn more about prolactin and breast cancer risk. 

Rates of breast cancer in the U.S. vary by race and ethnicity.

For example, overall, non-Hispanic white women and Non-Hispanic Black women have the highest rates of breast cancer incidence (rate of new breast cancer cases) and Hispanic women have the lowest incidence [324].

Learn more about race, ethnicity, and breast cancer risk.

People exposed to large amounts of radiation early in life, such as radiation treatment to the chest area for childhood cancer, have an increased risk of breast cancer [299-300,307-308].

For example, women treated with radiation therapy to the chest area for Hodgkin lymphoma (Hodgkin’s disease) at a young age have a 3-7 times higher risk of breast cancer than women who had Hodgkin lymphoma at a young age, but were not treated with radiation therapy [299].

People exposed to very low doses of radiation (such as from X-rays) don’t have much, if any, increase in breast cancer risk [224-225].

Learn more about radiation treatment in youth and breast cancer risk.

Learn more about radiation exposure from mammography and other medical imaging and breast cancer risk.

Learn about occupational exposure to radiation and breast cancer risk.

Women who smoke for many years have a slightly increased risk of breast cancer [312-318].

Women who are current smokers and have been smoking for more than 10 years appear to have about a 10% higher risk of breast cancer than women who’ve never smoked [314,316-317].

Learn more about smoking and breast cancer risk.

Learn about smoking and breast cancer survival.

Where do the data come from?

Human studies

The data in this section come from 2 main types of research studies:

The goal of these studies is to give information that helps support or disprove an idea about a possible link between an exposure (such as alcohol use) and an outcome (such as breast cancer) in people.

Although they have the same goal, observational studies and randomized controlled trials differ in:

  • The way they’re conducted
  • The strength of the conclusions they reach

Learn more about different types of research studies.

Animal studies

Animal studies add to our understanding of how and why some factors may be linked to cancer in people.

However, there are many differences between animals and people, so it’s hard to translate findings directly from one to the other.

Animal studies are also designed differently. They often look at exposures in larger doses and for shorter periods of time than are suitable for people.

While animal studies can lay the groundwork for research in people, we need human studies to draw conclusions for people.

All the data you see in this section of the website come from human studies.

Finding information on risk factors

Susan G. Komen® has up-to-date information on many established, probable and possible risk factors for breast cancer. Komen also has information on many factors not related to risk.

Other health organizations conduct research and/or prepare detailed summary reports of research on certain factors shown to have a link (or no link) to breast cancer and other types of cancer, including:

IARC is a part of the World Health Organization. The CDC, NTP and FDA are all part of the U.S. Department of Health and Human Services. World Cancer Research Fund International is a non-profit organization.

To learn more about the role of the environment in breast cancer, Susan G. Komen® sponsored a study from the National Academies of Sciences, Engineering, and Medicine (formerly the Institute of Medicine), “Breast Cancer and the Environment, a Life Course Approach.”

Updated 04/26/24

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