The Who, What, Where, When and Sometimes, Why.

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 suggest 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

 

Increases breast cancer risk

 

Decreases breast cancer risk

 

Not related to breast cancer risk (neither increases nor decreases risk)

  

Established and Probable Factors

Increases breast cancer risk 
(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 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

Decreases breast cancer risk 
(Listed alphabetically.) 

Body weight (heavier) before menopause

Exercise (physical activity) after menopause

Breastfeeding

Fruits and vegetables  

Carotenoids

 

Not related to breast cancer risk (does not increase or decrease risk) 
(Listed alphabetically.)  

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

Deodorant and antiperspirant use

 

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

 

Increases breast cancer risk

 

Decreases breast cancer risk

 

Not related to breast cancer risk (neither increases nor decreases risk)

Possible Factors

Increases breast cancer risk
(Listed alphabetically.)  

Blood estrogen levels (high) before menopause

Insulin levels (high) after menopause

Hair dyes and hair relaxers

Meat consumption before menopause

Decreases breast cancer risk
(Listed alphabetically.)

Exercise (physical activity) before menopause

Vitamin D

Not related to breast cancer risk (does not increase or decrease risk)
(Listed alphabetically.)  

Anti-depressants

Fertility drugs

Aspirin

Fiber

Dairy products

Insulin levels (high) before menopause

Diabetes

Meat consumption after menopause

Dietary fat

Soy

 

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

Acrylamide (found in foods such as French fries)

Moles (on the skin)

Antibiotic use

Parabens (found in some body care products and cosmetics)  

Breast size

Plastics and BPA (bisphenol A)

Breastfed as an infant

Secondhand smoke exposure

DES (in utero exposure and breast cancer risk among offspring)

Stress

Folate, folic acid and multivitamins

 

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 that 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 that 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 that 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 cause 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 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. 

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 03/04/21

TOOLS & RESOURCES

Give for Metastatic Breast Cancer Research

Donate Now