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A risk factor is anything that increases your chances of getting a disease, such as breast cancer. But having a risk factor, or even many, does not mean that you are sure to get the disease.

Some risk factors for breast cancer are things you cannot change, such as getting older or inheriting certain gene changes. These make your risk of breast cancer higher.

For information on other known and possible breast cancer risk factors, see:

• Lifestyle-related Breast Cancer Risk Factors
• Factors with Unclear Effects on Breast Cancer Risk
• Disproven or Controversial Breast Cancer Risk Factors

Being born female

This is the main risk factor for breast cancer. Men can get breast cancer, too, but this disease is much more common in women than in men.

Getting older

As you get older, your risk of breast cancer goes up. Most breast cancers are found in women age 55 and older.

Inheriting certain gene changes

About 5% to 10% of breast cancer cases are thought to be hereditary, meaning that they result directly from gene changes (mutations) passed on from a parent.

BRCA1 and BRCA2: The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 or BRCA2 gene. In normal cells, these genes help make proteins that repair damaged DNA. Mutated versions of these genes can lead to abnormal cell growth, which can lead to cancer.

• If you have inherited a mutated copy of either gene from a parent, you have a higher risk of breast cancer.
• On average, a woman with a BRCA1 or BRCA2 gene mutation has up to a 7 in 10 chance of getting breast cancer by age 80. This risk is also affected by how many other family members have had breast cancer. (It goes up if more family members are affected.)  
• Women with one of these mutations are more likely to be diagnosed with breast cancer at a younger age, as well as to have cancer in both breasts.
• Women with one of these gene changes also have a higher risk of developing ovarian cancer and some other cancers. (Men who inherit one of these gene changes also have a higher risk of breast and some other cancers.)
• In the United States, BRCA mutations are more common in Jewish people of Ashkenazi (Eastern Europe) origin than in other racial and ethnic groups, but anyone can have them.

Other genes: Other gene mutations can also lead to inherited breast cancers. These gene mutations are much less common, and most of them do not increase the risk of breast cancer as much as the BRCA genes.

• ATM: The ATM gene normally helps repair damaged DNA (or helps kill the cell if the damaged can't be fixed). Inheriting 2 abnormal copies of this gene causes the disease ataxia-telangiectasia. Inheriting one abnormal copy of this gene has been linked to a high rate of breast cancer in some families.
• PALB2: The PALB2 gene makes a protein that interacts with the protein made by the BRCA2 gene. Mutations in this gene can lead to a higher risk of breast cancer.
• TP53: The TP53 gene helps stop the growth of cells with damaged DNA. Inherited mutations of this gene cause Li-Fraumeni syndrome. People with this syndrome have an increased risk of breast cancer, as well as some other cancers such as leukemia, brain tumors, and sarcomas (cancers of bones or connective tissue). This mutation is a rare cause of breast cancer.
• CHEK2: The CHEK2 gene is another gene that normally helps with DNA repair. A CHEK2 mutation increases breast cancer risk.
• PTEN: The PTEN gene normally helps regulate cell growth. Inherited mutations in this gene can cause Cowden syndrome, a rare disorder that puts people at higher risk for both cancer and benign (non-cancer) tumors in the breasts, as well as growths in the digestive tract, thyroid, uterus, and ovaries.
• CDH1: Inherited mutations in this gene cause hereditary diffuse gastric cancer, a syndrome in which people develop a rare type of stomach cancer. Women with mutations in this gene also have an increased risk of invasive lobular breast cancer.
• STK11: Defects in this gene can lead to Peutz-Jeghers syndrome. People affected with this disorder have pigmented spots on their lips and in their mouths, polyps (abnormal growths) in the urinary and digestive tracts, and a higher risk of many types of cancer, including breast cancer.

Inherited mutations in several other genes have also been linked to breast cancer, but these account for only a small number of cases.

Genetic counseling and testing: Genetic testing can be done to look for inherited mutations in the BRCA1 and BRCA2 genes (or less commonly in genes such as PTEN, TP53, or others mentioned above). This might be an option for some women who have been diagnosed with breast cancer, as well as for certain women with factors that put them at higher risk for breast cancer, such as a strong family history. While genetic testing can be helpful in some cases, not every woman needs to be tested, and the pros and cons need to be considered carefully. To learn more, see Genetic Counseling and Testing for Breast Cancer Risk.

Having a family history of breast cancer

It’s important to note that most women who get breast cancer do not have a family history of the disease. But women who have close blood relatives with breast cancer have a higher risk:

• Having a first-degree relative (mother, sister, or daughter) with breast cancer almost doubles a woman’s risk. Having 2 first-degree relatives increases her risk by about 3-fold.
• Women with a father or brother who has had breast cancer also have a higher risk of breast cancer.

Having a personal history of breast cancer

A woman with cancer in one breast has a higher risk of developing a new cancer in the other breast or in another part of the same breast. (This is different from a recurrence or return of the first cancer.) Although this risk is low overall, it's even higher for younger women with breast cancer.

Race and ethnicity

Overall, White women are slightly more likely to develop breast cancer than African American women, although the gap between them has been closing in recent years. In women under age 40, breast cancer is more common in African American women. African American women are also more likely to die from breast cancer at any age. Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.

Risk in different groups also varies by type of breast cancer. For example, African American women are more likely to have the less common triple-negative breast cancer.

Being taller

Many studies have found that taller women have a higher risk of breast cancer than shorter women. The reasons for this aren’t exactly clear, but it may have something to do with factors that affect early growth, such as nutrition early in life, as well as hormonal or genetic factors.

Having dense breast tissue

Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. Breasts appear denser on a mammogram when they have more glandular and fibrous tissue and less fatty tissue. Women with dense breasts on mammogram have a higher risk of breast cancer than women with average breast density. Unfortunately, dense breast tissue can also make it harder to see cancers on mammograms.

A number of factors can affect breast density, such as age, menopausal status, the use of certain drugs (including menopausal hormone therapy), pregnancy, and genetics.

To learn more, see our information on breast density and mammograms.

Having certain benign breast conditions

Women diagnosed with certain types of benign (non-cancer) breast conditions may have a higher risk of breast cancer. Some of these conditions are more closely linked to breast cancer risk than others. Doctors often divide benign breast conditions into different groups, depending on how they affect this risk.

Non-proliferative lesions: These conditions don’t seem to affect breast cancer risk, or if they do, the increase in risk is very small. They include:

• Fibrosis and/or simple cysts (sometimes called fibrocystic changes)
• Mild hyperplasia
• Adenosis (non-sclerosing)
• Phyllodes tumor (benign)
• A single papilloma
• Fat necrosis
• Duct ectasia
• Periductal fibrosis
• Squamous and apocrine metaplasia
• Epithelial-related calcifications
• Other tumors (lipoma, hamartoma, hemangioma, neurofibroma, adenomyoepithelioma)

Mastitis (infection of the breast) is not a tumor and does not increase the risk of breast cancer.

Proliferative lesions without atypia (cell abnormalities): In these conditions there’s excessive growth of cells in the ducts or lobules of the breast, but the cells don't look very abnormal. These conditions seem to raise a woman’s risk of breast cancer slightly. They include:

• Usual ductal hyperplasia (without atypia)
• Fibroadenoma
• Sclerosing adenosis
• Several papillomas (called papillomatosis)
• Radial scar

Proliferative lesions with atypia: In these conditions, the cells in the ducts or lobules of the breast tissue grow excessively, and some of them no longer look normal. These types of lesions include:

• Atypical ductal hyperplasia (ADH)
• Atypical lobular hyperplasia (ALH)

Breast cancer risk is about 4 to 5 times higher than normal in women with these changes. If a woman also has a family history of breast cancer and either hyperplasia or atypical hyperplasia, she has an even higher risk of breast cancer.

Lobular carcinoma in situ (LCIS)

In LCIS, cells that look like cancer cells are growing in the lobules of the milk-producing glands of the breast, but they are not growing through the wall of the lobules. LCIS is not considered to be cancer, and it typically does not spread beyond the lobule (that is, it doesn't become invasive breast cancer) if it isn’t treated. But women with LCIS have a 7 to 12 times higher risk of developing breast cancer (which can be in either breast).

For more on these conditions, see Non-cancerous Breast Conditions.

Starting menstrual periods early

Women who have had more menstrual cycles because they started menstruating early (especially before age 12) have a slightly higher risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the hormones estrogen and progesterone.

Going through menopause later

Women who have had more menstrual cycles because they went through menopause later (typically after age 55) have a slightly higher risk of breast cancer. The increase in risk may be because they have a longer lifetime exposure to the hormones estrogen and progesterone.

Having radiation to your chest

Women who were treated with radiation therapy to the chest for another cancer (such as Hodgkin or non-Hodgkin lymphoma) when they were younger have a significantly higher risk for breast cancer. This risk depends on their age when they got radiation. The risk is highest for women who had radiation as a teen or young adult, when the breasts were still developing. Radiation treatment in older women (after about age 40 to 45) does not seem to increase breast cancer risk.

Exposure to diethylstilbestrol (DES)

From the 1940s through the early 1970s some pregnant women were given an estrogen-like drug called DES because it was thought to lower their chances of losing the baby (miscarriage). These women have a slightly increased risk of developing breast cancer. Women whose mothers took DES while they were pregnant with them may also have a slightly higher risk of breast cancer.

To learn more, see our information about DES exposure.