What Are the Risk Factors for Breast Cancer?

Understand · Risk

Sourced from the CDC, the National Cancer Institute, the American Cancer Society, the World Health Organization, the U.S. Preventive Services Task Force, Breastcancer.org and a 2021 review in the journal Cancers. Last updated October 2026.

The short answer on breast cancer risk factors

The two biggest risk factors for breast cancer are being a woman and getting older, and nobody chooses either. Others include inherited gene changes, family history, dense breasts and chest radiation at a young age. A smaller set is tied to how we live: alcohol, weight after menopause, activity and some hormone medicines. A risk factor raises the odds. It doesn't decide what happens.

What to know about breast cancer risk factors

• Risk isn't fate. The CDC says most women have some risk factors, and most never get breast cancer.
• Inherited breast cancer is less common than people think. About 5% to 10% of cases are thought to be hereditary.
• Some factors weigh far more than others. A BRCA gene change counts for much more than when your periods started.
• Alcohol counts. Risk rises the more you drink, and no amount is completely safe.
• High risk has options. Medicines and, for a few people, surgery can lower it.

This piece is about the chance of a first breast cancer. If you've had breast cancer, the risk of it coming back is a different subject; see The Fear That It's Back. For mammograms and screening, see Your Top 10 Breast Cancer Questions, Answered.

What is a breast cancer risk factor?

A risk factor is anything that makes a disease more likely. The American Cancer Society adds that having one, or even several, doesn't mean you'll get breast cancer. The CDC says risk factors don't all carry the same weight, and some women develop breast cancer with none beyond being a woman and getting older.

How many? The World Health Organization estimates that about 80% of breast cancers worldwide occur in women with no specific risk factor besides sex and age. That cuts both ways. A clean family tree and a healthy routine don't make you immune, and a long list of risk factors doesn't mean a diagnosis is coming.

What are the biggest risk factors for breast cancer?

Being a woman. The ACS calls being born female the main risk factor. Men get breast cancer too, but the WHO puts them at only about 0.5% to 1% of cases.

Getting older. Risk rises with age. The CDC says most breast cancers are diagnosed after 50, and Breastcancer.org says about two out of three invasive breast cancers are found in women 55 or older.

How much do inherited genes raise breast cancer risk?

For a small group, a lot. The ACS and Breastcancer.org say about 5% to 10% of breast cancers are thought to be hereditary, caused by a gene change passed down from a parent.

BRCA1 and BRCA2 are the best-known. The ACS says women with a harmful change in either gene have up to a 70% chance of breast cancer in their lifetime. NCI lists other genes linked to higher risk, including PALB2, CHEK2, ATM, CDH1, PTEN, STK11 and TP53 (the gene behind Li-Fraumeni syndrome). They don't all weigh the same: the ACS calls ATM and CHEK2 moderate-risk genes. The ACS notes that women of Ashkenazi Jewish heritage are more likely to carry a BRCA change.

How does family history affect breast cancer risk?

Close relatives matter most. The ACS says having one first-degree relative with breast cancer (a mother, sister or daughter) almost doubles a woman's risk, and two can roughly triple it. A father or brother with breast cancer raises it too.

Age matters too: the ACS says a first-degree relative diagnosed before 30 roughly triples risk, while one diagnosed after 60 raises it much less. The CDC adds several relatives on the same side of the family, and a family history of ovarian cancer.

Still, family history is the exception. A 2021 review in Cancers put the share of people diagnosed who report a first-degree relative with breast cancer at only about 13% to 19%.

Which other breast cancer risk factors can't you change?

When your periods started and stopped. Starting periods early (Breastcancer.org says before 12) or reaching menopause late (the ACS says after 55) slightly raises risk. The CDC says it's about more years of hormone exposure.

Dense breasts. Breasts with more gland and fibrous tissue than fat carry higher risk, the CDC says, and can hide tumors on a mammogram.

Certain biopsy results. Atypical hyperplasia (ductal or lobular) means overgrown cells that look abnormal under a microscope. The ACS says it isn't cancer but carries about 4 to 5 times the usual risk, and most women with it never get breast cancer. Lobular carcinoma in situ (LCIS) isn't cancer either, despite the name: the abnormal cells stay inside the milk glands. The ACS says it carries about 7 to 12 times the usual risk, in either breast.

A past breast cancer. Breastcancer.org says women who've had breast cancer are three to four times more likely to develop a new cancer in the other breast or another part of the same breast. The ACS stresses that this is different from a recurrence.

Chest radiation before 30. The CDC names radiation to the chest before 30, such as for Hodgkin lymphoma. NCI counts it among the factors that carry very high risk.

DES. Diethylstilbestrol was given to some pregnant women in the U.S. from 1940 to 1971 to prevent miscarriage. The CDC says women who took it have a higher risk, and their daughters may too.

Race and ethnicity. NCI says White women in the U.S. have the highest rate of breast cancer, and Black women have the highest death rate. The ACS says that before 40, breast cancer is more common in Black women. Our Top 10 piece explains more.

Does alcohol raise breast cancer risk?

Yes. The CDC, NCI, the ACS and the WHO all list it. The ACS says risk rises with every drink, so two drinks a day raises it more than one, and that no amount of alcohol is completely safe. Its advice is that it's best not to drink, and that women who do should have no more than one drink a day.

Do weight and exercise affect breast cancer risk?

Weight after menopause. The CDC says being overweight or having obesity after menopause raises risk. The ACS explains the mechanism: after menopause the ovaries stop making estrogen, and most of the body's estrogen comes from fat tissue, so more fat can mean more estrogen. Oddly, the ACS says extra weight before menopause is linked to lower risk, for reasons that aren't clear.

Movement. The CDC links not being active to higher risk. The ACS recommends 150 to 300 minutes of moderate activity a week, or 75 to 150 minutes of vigorous activity.

Do hormone therapy and birth control raise breast cancer risk?

Menopausal hormone therapy. The type matters. The CDC and NCI both list combined estrogen-plus-progestin therapy as a risk factor. The ACS says risk is higher with longer use, higher doses and starting after 60, and that the decision should be made person by person.

Hormonal birth control. The ACS says the pill slightly raises risk while you take it, and that risk returns to normal within a few years of stopping. NCI files it under factors that need more study, because some studies find a slight increase and others don't. Either way, the effect is small and temporary.

Does smoking raise breast cancer risk?

Possibly, especially for younger women, though the evidence is less tidy than for alcohol. Breastcancer.org links smoking to higher risk in younger women before menopause. The ACS says the link has been hard to study because many people who smoke also drink, though some studies suggest smoking alone may raise risk.

Do pregnancy and breastfeeding affect breast cancer risk?

They're on every risk factor list, so here they are, with a caveat. Whether and when you have children, and whether you breastfeed, are life circumstances and choices, shaped by health, fertility, money, work, relationships and luck. Nobody should feel blamed for them, or pressured by a risk table.

The CDC lists a first pregnancy after 30, never carrying a pregnancy to term and not breastfeeding. The ACS sets the bar a little differently: it says never being pregnant, or a first pregnancy at 35 or later, slightly raises risk compared with a first child in your 20s. It adds that breastfeeding may slightly lower risk, especially for a year or more. These are modest effects.

What has been ruled out as a cause of breast cancer?

The ACS says there's little if any reason to think antiperspirants raise risk, and no evidence that bras do. It says abortion doesn't affect breast cancer risk, and that breast implants haven't been shown to raise it. Environmental chemicals, diet and night shift work are still being studied; our Top 10 piece has more.

What should you do about your breast cancer risk factors?

Learn your family history, on both sides. Note who had breast, ovarian or male breast cancer, and their age at diagnosis.

Ask for a risk assessment. Your clinician can tell you whether your risk is average or higher, which shapes how you're screened.

Ask about genetic counseling if there are red flags. NCI says a genetic counselor can help assess whether you're likely to carry a gene change, talk through testing and explain results, including for your relatives.

Work on what you can, without guilt. Drinking less, moving more and avoiding weight gain after menopause can shift the odds. None of it is a guarantee, and a diagnosis is never a verdict on how you lived.

How can people at high risk lower their chance of breast cancer?

Medicines. The U.S. Preventive Services Task Force (2019; an update is in progress) recommends that clinicians offer tamoxifen, raloxifene or an aromatase inhibitor to women 35 and older who are at increased risk and at low risk of side effects, and recommends against them for everyone else. Only tamoxifen is for women before menopause. The task force says these medicines lower the risk of estrogen receptor-positive breast cancer, but tamoxifen and raloxifene raise the risk of blood clots, and tamoxifen raises the risk of uterine cancer.

Surgery. For people at very high risk, such as those with a BRCA change or chest radiation before 30, the ACS says preventive mastectomy can lower breast cancer risk by 90% or more, though not to zero. It says removing the ovaries and tubes is usually recommended for BRCA carriers once they're done having children. These are big decisions, and a second opinion is reasonable.

Screening. The CDC says people at high risk should talk with a doctor about screening as well as medicines and surgery.

When to see a clinician about a breast change

• A new lump in your breast or armpit
• Thickening or swelling in part of your breast
• Irritated or dimpled skin on your breast
• Redness or flaky skin on the nipple or breast
• A nipple that pulls inward, or pain in the nipple area
• Nipple discharge that isn't breast milk, including blood
• Any change in the size or shape of your breast, or pain anywhere in it

The CDC says to see your doctor right away for any of these, whatever your risk. Conditions other than cancer can cause them too, which is why they deserve a proper look.

If it feels like an emergency, call 911.

Questions to ask your clinician about your breast cancer risk

1. Based on my history, is my breast cancer risk average, higher than average or high?
2. Does my family history, on either side, mean I should see a genetic counselor?
3. Do I have dense breasts, and does that change how I should be screened?
4. Does anything in my past, such as a biopsy result or chest radiation, raise my risk?
5. Does the hormone therapy or birth control I'm using or considering change my risk?
6. Am I a candidate for a medicine to lower my risk? What are the side effects?

Sources: CDC, Breast Cancer Risk Factors and Symptoms of Breast Cancer (both reviewed September 22, 2026); National Cancer Institute, Breast Cancer Causes and Risk Factors (updated December 2, 2025); American Cancer Society, Breast Cancer Risk and Prevention (revised March 19, 2026), Breast Cancer Risk Factors You Cannot Change, Breast Cancer Risk Factors You Can Change (revised June 11, 2026), Unclear, Disproven, and Controversial Breast Cancer Risk Factors, Hyperplasia of the Breast (Ductal or Lobular) (revised May 26, 2026), Lobular Carcinoma in Situ (LCIS) (revised July 17, 2026), Preventive Surgery to Reduce Breast Cancer Risk and Breast Cancer Risk and Prevention (PDF, revised September 6, 2017); World Health Organization, Breast cancer fact sheet (July 3, 2026); U.S. Preventive Services Task Force, Breast Cancer: Medication Use to Reduce Risk (September 2019; update in progress); Breastcancer.org, Breast Cancer Risk Factors (updated June 11, 2026); Łukasiewicz et al., Breast Cancer—Epidemiology, Risk Factors, Classification, Prognostic Markers, and Current Treatment Strategies—An Updated Review, Cancers (August 2021). This article is general information, written in Babette's own words, and is not a substitute for advice from your care team.