Breast Cancer Risk Factors Table

The table below lists factors linked (or not linked in some cases) to breast cancer. It also lists many factors still under study.

Factors are grouped based on the strength of the scientific evidence:

Established and probable factors have the strongest evidence behind them. They are recognized as linked (or not linked in some cases) to breast cancer.
Possible factors have less evidence behind them. They have suggested links to breast cancer, but need more study before solid conclusions can be made.
Insufficient or inconsistent factors are backed by few studies or the studies to date show mixed results, so there’s not enough evidence to allow comment on possible links to breast cancer.

Click on any of the factors below to learn more.

Established and probable factors

Recognized as linked (or not linked in some cases) to breast cancer.

Legend
	Linked to an increased risk of breast cancer
	Linked to a decreased risk of breast cancer
	Not related to breast cancer risk (not linked to an increased or decreased risk)

Established and Probable Factors
Linked to an increased risk of breast cancer (Listed alphabetically.)
Age (older)	Breast density (high)
Age at first childbirth (older)	Family history of breast cancer
Age at first period (younger)	Height (taller)
Age at menopause (older)	Hyperplasia (benign breast condition)
Alcohol	IGF-1 hormone levels (high)
Anti-Müllerian hormone (AMH) levels (high)	Light at night and shift work
Ashkenazi Jewish heritage	Lobular carcinoma in situ (LCIS)
Being born female	Menopausal hormone therapy – estrogen plus progestin
Birth control pills (current or recent use)	Personal history of cancer
Birthweight (high)	Prolactin hormone levels (high)
Blood androgen levels (high)	Race and ethnicity
Blood estrogen levels (high) after menopause	Radiation exposure from medical imaging
Body weight (heavier) after menopause	Radiation treatment during youth
Bone density (high)	Smoking
BRCA1, BRCA2 or other high-risk inherited gene mutation	Weight gain
Linked to a decreased risk of breast cancer (Listed alphabetically.)
Body weight (heavier) before menopause	Exercise (physical activity) after menopause
Breastfeeding	Fruits and vegetables
Carotenoids
Not related to breast cancer risk (not related to an increased or decreased risk) (Listed alphabetically.)
Acrylamide (found in foods such as French fries)	Deodorant and antiperspirant use
Abortion	Electromagnetic fields (from utility wires, electric blankets, etc.)
Blood organochlorine levels (exposure to certain types of pesticides and industrial chemicals)	Left-handedness
Bras or underwire bras	Menopausal hormone therapy – estrogen only (less than 10 years of use)
Breast implants	Migraine headaches
Caffeine (coffee and tea)	Sugar
Cell phone use	Trauma to the breast

Possible factors

Recognized as potentially linked (or not linked in some cases) to breast cancer. More study is needed before solid conclusions can be made. These factors are still under study.

Legend
	Linked to an increased risk of breast cancer
	Linked to a decreased risk of breast cancer
	Not related to breast cancer risk (not linked to an increased or decreased risk)

Possible Factors
Linked to an increased risk of breast cancer (Listed alphabetically.)
Blood estrogen levels (high) before menopause	Insulin levels (high) after menopause
Diabetes after menopause	Meat consumption before menopause
Linked to a decreased risk of breast cancer (Listed alphabetically.)
Exercise (physical activity) before menopause	Vitamin D
Not related to breast cancer risk (not related to an increased or decreased risk) (Listed alphabetically.)
Anti-depressants	Fiber
Aspirin	Hair dyes and hair relaxers
Dairy products	Insulin levels (high) before menopause
Diabetes before menopause	Meat consumption after menopause
Dietary fat	Soy
Fertility drugs

Factors with inconsistent results or insufficient evidence

For these factors, there are few studies or study results are very mixed. More research is needed to comment on any possible link to breast cancer.

(Listed alphabetically.)

Factors with Inconsistent Results or Insufficient Evidence
Antibiotic use	Moles (on the skin)
Breast size	Parabens (found in some body care products and cosmetics)
Breastfed as an infant	Plastics and BPA (bisphenol A)
DES (in utero exposure and breast cancer risk among offspring)	Secondhand smoke exposure
Folate, folic acid and multivitamins	Stress

Level of scientific evidence to support a link with breast cancer risk
Established factors	Consistent epidemiologic findings across a large number of well-designed studies Demonstrates a dose-response relationship (as the factor increases/decreases, risk also increases/decreases) Biologically plausible mechanisms (there’s a clear biological reason the factor might be linked to risk) Supportive laboratory evidence (animal and/or cell studies)
Probable factors	Epidemiologic evidence is largely consistent, but not extensive enough to make definitive judgment Biologically plausible mechanisms (there’s a clear biological reason the factor might be linked to risk) Supportive laboratory evidence (animal and/or cell studies)
Possible factors	Epidemiologic findings are supportive, but limited in quantity or quality Results are generally consistent, but only hint at a possible relationship Supportive laboratory evidence may or may not be available May not be a clear biological reason the factor might be linked to risk
Factors with inconsistent findings or insufficient evidence	Very few available studies and/or results are highly inconsistent More research is needed to comment on any potential relationship
Adapted from criteria outlined by the International Agency for Research on Cancer (IARC).

Where do the data come from?

Human studies

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

Observational studies (cohort or case-control)
Randomized controlled trials

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 are 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 makes it 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 presented within the About Breast Cancer section of this website come from studies of people.

Finding information on risk factors

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

Other 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, 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 04/12/23

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