Many factors have been studied to see whether or not they increase the risk of breast cancer.
Some of these factors have been proven to be unrelated to breast cancer and do not increase risk. Some may even decrease risk (although these findings are not yet conclusive).
A full list of factors that don't increase breast cancer risk is too long to present here. Some, however, deserve mention because they have been studied more than most or they have gotten a lot of media attention.
Our Breast Cancer Risk Factors Table compares factors by level of risk and strength of evidence.
The factors below are listed alphabetically.
Research clearly shows abortion (also called induced abortion) does not increase breast cancer risk .
Since 2003, the American College of Obstetricians and Gynecologists (ACOG) and the National Cancer Institute (NCI) have agreed the scientific evidence does not support a link between abortion and breast cancer [506-508]. ACOG reaffirmed its conclusion there’s no link between abortion and breast cancer in 2018 .
Some case-control studies have suggested abortion may increase the risk of breast cancer . However, the design of case-control studies makes the accuracy of their results questionable.
Case-control studies rely on the reporting of past behavior. When it comes to a sensitive subject like abortion, this can have a big impact on the information gathered.
The cases in these studies (the women with breast cancer) may be more likely to give complete information about their abortion history than the controls (the women without breast cancer). The controls may not be as comfortable sharing this personal information as the women diagnosed with breast cancer who are interested in whether personal health history is related to breast cancer. Such differences in reporting can bias study results.
Prospective cohort studies are much more likely to give accurate results on topics such as abortion. These studies gather sensitive information before women are diagnosed with breast cancer. This helps limit biased reporting.
Cohort studies show abortion does not increase the risk of breast cancer [505,510-519].
Cohort studies and a large pooled analysis have shown miscarriage (also called spontaneous abortion) does not increase the risk of breast cancer [510,512,515-517].
These findings support the evidence that abortion does not increase risk.
Since 2003, the NCI has concluded the evidence does not support a link between miscarriage and breast cancer . The NCI routinely reviews the evidence on this topic (most recently in 2016) and continues to agree the evidence does not support a link between the two .
Environmental pollutants have been suggested as potential causes of breast cancer because many of these compounds have estrogen-like traits.
Some of the most common and well-studied environmental pollutants are organochlorines. They include:
A good way to measure exposure to these chemicals is by looking at their levels in a person's blood.
The results of most studies looking at blood organochlorine levels and risk of breast cancer, including the Long Island Breast Cancer Study, have found no link [520-528].
A breast cancer cluster is a small area, such as a town or county, where the rates of breast cancer are higher than the U.S. average. Sometimes a cluster is found and it raises interest in possible environmental causes of breast cancer.
Two of the best-studied breast cancer clusters are in Long Island, New York and Marin County, California (San Francisco Bay area) [524,529]. In the 1990s, rates of new cases of breast cancer were higher than expected in these areas.
Many studies looked at known risk factors and possible environmental factors (including organochlorines and electromagnetic fields) that might be related to the excess number of breast cancer cases in these areas.
The Long Island and Marin Country clusters were explained by differences in risk factors such as family history of breast cancer, use of menopausal hormone therapy (postmenopausal hormones) and age at first childbirth [524,529].
To date, no environmental toxins related to breast cancer have been found.
This doesn’t mean there are no environmental pollutants that may increase the risk of breast cancer. However, most clusters have been explained by differences in known risk factors.
Learn more about breast cancer and the environment.
For a summary of research studies on environmental pollutants and breast cancer, visit the Breast Cancer Research Studies section.
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.
Scientific evidence does not support a link between wearing an underwire bra (or any type of bra) and breast cancer risk . There's no biological reason they would be linked.
A 1991 case-control study found women who didn't wear bras had a lower risk of breast cancer than women who did wear bras . However, the authors stated this link was likely due to factors related to wearing a bra rather than the bra itself.
The women in the study who didn't wear a bra were more likely to be thin, which the authors concluded might account for their decreased risk of breast cancer .
Although wearing a bra does not appear to be linked to breast cancer risk, breast size is under study as a potential risk factor.
Neither saline nor silicone breast implants increase breast cancer risk [532-538].
Findings from prospective cohort studies and a meta-analysis of 10 studies of cosmetic breast implants (including studies of both saline and silicone implants) have found no increased breast cancer risk among women with implants [532-538].
A few studies have found a decreased risk of breast cancer among women with breast implants [536-538]. This decreased risk is most likely due to traits of women who tend to choose breast implants (such as being thin). These traits likely lower the risk of breast cancer rather than the implants themselves .
Anaplastic large cell lymphoma (ALCL) is a very rare cancer of the cells of the immune system [540-542]. When ALCL occurs in women with breast implants it’s called breast implant-associated ALCL (BIA-ALCL). BIA-ALCL is treatable.
Estimates of the risk of BIA-ALCL occurring in women with breast implants vary widely from 1 in 3,817 to 1 in 30,000 . These estimates are based on confirmed cases known to date .
The U.S. Food and Drug Administration (FDA) is studying the link between breast implants (both saline and silicone) and a slight increase in risk of BIA-ALCL .
Although the reasons are unclear, the risk of BIA-ALCL appears to be linked to textured breast implants rather than smooth implants [540-543].
The FDA doesn’t recommend special care for women with breast implants (nor does it recommend removing implants) . However, if you have breast implants and feel any pain around the implants or notice any changes to your implants, see your health care provider.
If you are considering breast implants, talk with your provider about the benefits and risks of textured implants and smooth implants.
For a summary of research studies on breast implants and breast cancer, visit the Breast Cancer Research Studies section.
Most cohort studies to date have found no link between drinking either coffee or tea and the risk of breast cancer [544-553].
Learn more about caffeine.
Learn more about diet and breast cancer.
A meta-analysis that combined the results of 37 studies found no link between caffeine or coffee intake and breast cancer risk .
Some studies have found women who drink a lot of coffee (with caffeine) have a lower risk of breast cancer compared to non-coffee drinkers [555-557].
A meta-analysis that combined the results of 15 studies found no link between drinking tea and breast cancer risk .
Studies show no link between cell phone use and the risk of breast cancer [559-560].
Research on deodorant and antiperspirant use and breast cancer risk was driven by concerns about chemicals found in these products.
However, studies have found no link between deodorant or antiperspirant use and breast cancer risk [561-562].
People are exposed to electromagnetic fields (EMF) in different ways, such as through utility wires, microwave ovens, fluorescent lighting and electric blankets.
Regular exposure to EMF does not appear to increase the risk of breast cancer [563-567]. Large cohort studies and a meta-analysis that combined the results of 15 studies have found no link [563-567].
For a summary of research studies on electromagnetic fields and breast cancer, visit the Breast Cancer Research Studies section.
Many studies, including a meta-analysis that combined the results of 14 studies, have found no link between permanent hair dyes and the risk of breast cancer [568-571].
There also appears to be no link between the use of hair relaxers and the risk of breast cancer among African-American women [572-573].
For a summary of research studies on hair dyes and breast cancer, visit the Breast Cancer Research Studies section.
Although it's not clear why, breast cancer is slightly more likely to occur in the left breast compared to the right breast .
This difference prompted a theory that being left-handed may increase breast cancer risk.
However, studies have found no link between being left-handed and breast cancer risk [531,575-576]. Further, being left-handed is not linked to reproductive factors related to breast cancer risk (such as age at first period or age at menopause) [576-577].
Migraine headaches may be related to changing estrogen levels in a woman’s body. Since estrogen is related to breast cancer risk, migraines have been studied as a possible risk factor for breast cancer .
However, a meta-analysis of findings from 3 large cohort studies found no difference in breast cancer risk between women with and without a history of migraines .
Learn more about estrogen and breast cancer risk.
Eating sugar does not make cancer cells grow [579-580].
A recent cohort study found no difference in breast cancer risk between women who ate a lot of sugar (or drank a lot of sugar-sweetened beverages) and those who consumed little sugar .
However, eating a lot of sugar (or drinking a lot of sugar-sweetened beverages) can lead to weight gain, which can increase the risk of breast cancer [75-78].
Limiting high-calorie foods and beverages (including those with a lot of sugar) is part of a healthy diet .
Learn more about body weight and breast cancer risk.
Learn more about a healthy lifestyle and breast cancer.
The data in this section come from 2 main types of research studies:
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:
Learn more about different types of research 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 this section of the website come from studies done with people.
Susan G. Komen® has up-to-date information on many established, probable and possible risk factors for breast cancer (and information on many factors shown not to increase risk).
Other organizations conduct research and/or prepare detailed summary reports of research on factors shown to have a link (or no link) to breast 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, Susan G. 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."
Facts for Life: Breast Cancer Risk Factors
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