The Main Risk Factors for Breast Cancer

Breast cancer develops when cells in breast tissue grow abnormally and form a tumor. Doctors do not yet fully understand why this happens in some people and not others, but research has identified several factors that raise the risk. These are called risk factors—they make the disease more likely, but having one or more does not mean you will definitely get breast cancer.

The strongest risk factors are age, sex, and family history. Being female and getting older both significantly raise risk. If your mother, sister, or daughter had breast cancer, your own risk is higher. Beyond these, factors like hormone use, alcohol, weight, and reproductive history also play a role. Understanding these factors can help you talk with your doctor about your personal risk and what screening might be right for you.

Key Takeaways

  • Age and female sex are the strongest risk factors—most breast cancers occur in women over 50.
  • A family history of breast cancer, especially in a close relative, meaningfully raises your risk.
  • Hormone replacement therapy and birth control pills slightly raise risk, while pregnancy and breastfeeding lower it.
  • Alcohol use, being overweight after menopause, and not exercising regularly are modifiable factors you can discuss with your doctor.
  • Having a risk factor does not mean you will get breast cancer—many people with risk factors never develop the disease.

Age and Sex

Breast cancer is far more common in women than men, though men can develop it. The risk rises sharply with age. Most breast cancers are diagnosed in women over 50, and the average age at diagnosis is around 62. This does not mean younger women cannot get breast cancer—they can—but it is less common.

The reason age matters is that cells accumulate damage over time. The longer you live, the more chances your cells have to develop the changes that lead to cancer. This is why screening recommendations typically begin at age 40 to 50, depending on your personal risk factors and your doctor's guidance.

Family History and Inherited Gene Changes

If a close relative—mother, sister, or daughter—had breast cancer, your risk is higher than average. The risk is even higher if that relative was diagnosed before age 50, or if multiple family members had the disease. This is because some families carry inherited gene changes that make breast cancer more likely.

The most well-known inherited changes are in the BRCA1 and BRCA2 genes. People who inherit a change in one of these genes have a much higher lifetime risk of breast cancer. Genetic testing can tell you whether you carry these changes, but it is not routine—your doctor will recommend it based on your family history. Other inherited gene changes also raise risk, though they are less common than BRCA mutations.

Hormones and Reproductive History

Estrogen and progesterone, the hormones that regulate the menstrual cycle and pregnancy, influence breast cancer risk. The longer your lifetime exposure to these hormones, the higher your risk. This is why starting your period early or going through menopause late raises risk slightly—both extend the years you produce these hormones.

Pregnancy and breastfeeding actually lower risk. Women who have never been pregnant have a higher risk than those who have. Using birth control pills or hormone replacement therapy (HRT) raises risk slightly while you are using them, and the risk returns to baseline after you stop. The increase is small, but it is real enough that you should discuss the pros and cons with your doctor if you have other risk factors.

Alcohol, Weight, and Physical Activity

Drinking alcohol raises breast cancer risk, and the risk increases with how much you drink. Even moderate drinking—one or two drinks per day—raises risk slightly. The exact reason is not fully clear, but alcohol may affect hormone levels and how your body processes certain chemicals.

Being overweight or obese after menopause raises risk, because fat tissue produces estrogen. Before menopause, being overweight does not raise risk in the same way. Regular physical activity lowers risk, independent of weight. These are factors you can influence through lifestyle choices, which is why your doctor may discuss them with you as part of your overall health plan.

Previous Breast Disease and Radiation Exposure

If you have had certain non-cancerous breast conditions—particularly those involving abnormal cell growth—your risk of breast cancer is higher. Your doctor can tell you whether any condition you have had falls into this category by reviewing your biopsy results.

Radiation to the chest raises risk, especially if exposure happened when you were young. This includes radiation from medical imaging (like repeated chest X-rays or CT scans) or from cancer treatment to the chest area. A single mammogram or chest X-ray carries minimal risk, but multiple exposures over time do add up. If you have had chest radiation for any reason, tell your doctor, as this affects your screening plan.

Race, Ethnicity, and Other Factors

Breast cancer rates and outcomes differ by race and ethnicity. Black women have higher death rates from breast cancer than white women, even though white women are diagnosed slightly more often. This difference is driven by factors like later-stage diagnosis, differences in access to care, and biological differences in tumor behavior—not by race itself.

Other factors that may raise risk include dense breast tissue (which is visible on mammograms), certain hormonal conditions, and exposure to the chemical diethylstilbestrol (DES) before birth. Your doctor can assess your individual risk based on your full medical history and help you decide on screening and prevention strategies that make sense for you.

Frequently Asked Questions

Does having one risk factor mean I will get breast cancer?

No. Risk factors make the disease more likely, but most people with risk factors never develop breast cancer. Having multiple risk factors raises your chances more than having just one, but it still does not may provide you will get sick. Your doctor can help you understand your personal risk level.

Can men get breast cancer?

Yes, though it is rare—about 1 in 100 breast cancers occur in men. Men have breast tissue just as women do, and the same risk factors apply, including age, family history, and hormone exposure. Men should report any changes in their chest area to a doctor.

If my mother had breast cancer, will I definitely get it?

No. Having a mother with breast cancer raises your risk, but many daughters of breast cancer patients never develop the disease. Your risk depends on other factors too, including her age at diagnosis and whether she carried an inherited gene change. Your doctor can assess your specific risk.

Does birth control cause breast cancer?

Birth control pills raise breast cancer risk slightly while you are taking them. The increase is small, and risk returns to baseline after you stop. For most women, the benefits of birth control outweigh this small risk, but you should discuss it with your doctor if you have other risk factors.

Can I lower my breast cancer risk?

You cannot change age, sex, or family history, but you can influence some risk factors. Limiting alcohol, maintaining a healthy weight, exercising regularly, and breastfeeding if you have children all lower risk. Talk with your doctor about screening and prevention options based on your personal risk profile.