Factors That Affect Breast Cancer Risk
Some factors affect breast cancer risk a great deal and others by only a small amount.
Some risk factors you can’t change. For example, the most common risk factors for breast cancer are being a woman and getting older.
Other factors you may be able to control. For example, leading a healthy lifestyle may help lower your risk of breast cancer.
Understanding which factors may affect your risk can help you work with your health care provider to address any concerns and develop a breast cancer screening plan that’s right for you.
Our Breast Cancer Risk Factors Table compares factors by level of risk and strength of evidence.
Risk factors are listed below alphabetically.
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 children a woman gives birth to affect her breast cancer risk.
Women who give birth to their first child at age 35 or younger tend to get a protective benefit from pregnancy [6-11].
In general, the more children a woman has given birth to, the lower her risk of breast cancer tends to be [6-11].
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 [10,14-18].
For example, women who began their periods before age 11 have about a 15-20 percent higher breast cancer risk than those who began their periods at age 15 or older [18].
Learn more about age at first period and breast cancer risk.
Going through menopause at a later age increases the risk of breast cancer [10,16,20].
For example, women who go through menopause after age 55 have about a 40 percent higher risk of breast cancer than women who do so at age 45 or younger [18].
Learn more about age at menopause and breast cancer risk.
Drinking alcohol increases the risk of breast cancer [21].
For example, women who have 2-3 alcoholic drinks per day have about a 20 percent higher risk of breast cancer than women who don’t drink alcohol [21].
Learn more about alcohol and breast cancer risk.
Learn about alcohol and breast cancer survival.
In the U.S., Jewish women have a slightly higher risk of breast cancer than other women [27].
This increased risk is likely due to the high prevalence of BRCA1 and BRCA2 gene mutations in Jewish women of Eastern European descent (Ashkenazi Jews).
Learn more about Ashkenazi Jewish heritage, BRCA1/2 gene mutations and breast cancer risk.
Being female is the main risk factor for breast cancer.
Although men can get breast cancer, it’s about 100 times more common in women [34].
Learn more about being female and breast cancer risk.
Learn more about breast cancer in men.
Current or recent use of birth control pills slightly increases the risk of breast cancer [10,35-38].
For example, while women are taking birth control pills (and shortly thereafter), they have a 20-30 percent higher risk of breast cancer than women who have never used the pill [35,37-38].
Learn more about birth control pills and breast cancer risk.
Women with a higher birthweight (a woman’s weight when she was born) appear to have an increased risk of breast cancer (especially before menopause) [47-51].
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 that are important in sexual development.
Higher amounts of androgens in the blood may be linked to an increased risk of breast cancer in women [57-60].
Learn more about blood androgen levels and breast cancer risk.
Estrogens are natural hormones that are important in sexual development and other body functions.
Higher amounts of estrogen in the blood are linked to an increased risk of breast cancer in women after menopause [19]. Researchers are studying a possible link to breast cancer before menopause.
Learn more about blood estrogen levels and breast cancer risk.
Being overweight or obese affects the risk of breast cancer differently for premenopausal and postmenopausal women.
- Before menopause, being overweight or obese modestly decreases breast cancer risk [64-67].
- After menopause, being overweight or obese increases breast cancer risk [64-66].
Gaining weight in adulthood appears to increase the risk of breast cancer (both before and after menopause) [76-79].
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 60-80 percent higher risk of breast cancer compared to women with low bone density [97].
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 high breast density are 4-5 times more likely to get breast cancer than women with low breast density [99-100].
Learn more about breast density and breast cancer risk.
Breastfeeding lowers the risk of breast cancer, especially in premenopausal (before menopause) women [11,108-111].
Learn more about breastfeeding and breast cancer risk.
Women who get regular exercise (physical activity) have about a 10-20 percent lower risk of breast cancer than women who are not active [119-125].
Learn more about exercise and breast cancer risk.
Learn about exercise and breast cancer survival.
A family history of certain types of cancer can increase the risk of breast cancer. This increased risk may be due to genetics, shared lifestyle factors or other family traits.
Having a first-degree relative (male or female) with breast cancer or a first-degree female relative with ovarian cancer increases the risk of breast cancer [28,139-143].
Having a first-degree male relative with prostate cancer also increases the risk of breast cancer [28,144-145].
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 vegetables may slightly lower the risk of some breast cancers [151-153]. Eating fruits may also help lower breast cancer risk [150].
Carotenoids
Carotenoids are natural orange-red food pigments found in fruits and vegetables (like melons, carrots, sweet potatoes and squash). Beta-carotene is an example of a carotenoid.
Women with higher blood levels of carotenoids have a reduced risk of breast cancer compared to women with lower levels [158].
Learn more about fruits, vegetables, carotenoids and breast cancer risk.
Taller women have a higher risk of breast cancer than shorter women [10,64,85,166-173].
Learn more about height and breast cancer risk.
Benign breast conditions (also called benign breast diseases) are non-cancerous breast disorders. Some of these conditions increase the risk of breast cancer and others do not.
For example, women who have hyperplasia have an increased risk of breast cancer [174-177].
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.
Studies have found higher levels of IGF-1 in the blood may increase the risk of breast cancer [237-240].
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
- BRIP1
- BRCA1
- BRCA2
- CDH1
- CHEK2
- NBN
- 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 people who have a BRCA1 or BRCA2 gene mutation.
Women who routinely work night shifts for many years have a small increased risk of breast cancer [241-243].
More research is needed to understand which aspects of shift work may impact breast cancer risk.
One possible reason for the increased risk among these workers is their exposure to light at night.
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 cancer [246-247].
Learn more about LCIS and breast cancer risk.
Menopausal hormone therapy (MHT) is FDA-approved for the short-term relief of menopausal symptoms [254].
The main types of MHT are:
- Estrogen plus progestin
- Estrogen alone
Estrogen plus progestin increases the risk of both developing and dying from breast cancer [20,255-259].
Some studies have shown estrogen alone increases the risk of breast cancer [20,257-259]. However, one large study found a decreased risk [261].
Estrogen alone is only used by women who have had a hysterectomy because it increases the risk of uterine cancer.
MHT is not usually given to breast cancer survivors because it may increase the risk of recurrence [265-266].
Learn more about MHT and breast cancer risk.
Learn more about MHT and breast cancer recurrence.
Women who 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 [267-270].
Ductal carcinoma in situ (DCIS) is a non-invasive breast cancer. Women diagnosed with DCIS in the past have an increased risk of DCIS in the opposite breast [276-278]. They also have an increased risk of invasive cancer in either breast [276-280].
A personal history of Hodgkin’s disease, ovarian cancer and certain other cancers can also increase the risk of breast cancer [28,186,281-289].
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 [290-291].
Learn more about prolactin and breast cancer risk.
Rates of breast cancer in the U.S. vary by race and ethnicity.
White women and black women have the highest incidence (rate of new breast cancer cases) overall, while American Indian/Alaska Native women have the lowest incidence [299].
Learn more about race, ethnicity, and breast cancer risk.
Exposure to large amounts of radiation early in life, such as radiation treatment to the chest area for childhood cancer, increases the risk of breast cancer [283-284,292-293].
For example, women treated with radiation therapy to the chest area for Hodgkin’s at a young age have about 3-7 times the risk of breast cancer compared to women who had Hodgkin’s disease at a young age, but were never treated with radiation therapy [283].
Very low doses of radiation (such as from X-rays and other medical imaging) don’t have much, if any, impact on breast cancer risk [206,294-295].
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.
