Factors That Do Not Increase Risk of Breast Cancer
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Over the years, many factors have been purported to increase the risk of breast cancer. While many of these have been solidly linked to the disease, many others have not. Although a complete list of factors unproven to increase breast cancer risk is too long to list, some deserve to be singled out—either because they have received attention in the media or because they have been studied more extensively than most.
Hair dyes
Both cohort and case-control studies have consistently shown that the use of permanent hair dyes is not related the risk of breast cancer [248-251]. A recent analysis that combined the results of 14 studies confirmed these findings [252].
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For a summary of research studies on hair dyes and breast cancer, please visit the Breast Cancer Research section. |
Abortion
Although there has been some controversy in the past about the relationship between abortion and breast cancer risk, the current body of evidence now strongly supports no link between the two [253]-a conclusion further confirmed in a recent National Cancer Institute report [254].
While numerous case-control studies have suggested that abortion may moderately increase the risk of breast cancer [255], the nature of these studies makes the accuracy of their results questionable [253]. Case-control studies rely on the reporting of past behavior, and when it comes to a sensitive topic like abortion, this can have a significant impact on the precision of the information gathered. The cases in these studies-the women with breast cancer-may be much more likely to provide complete information about their abortion history than the controls-the women without breast cancer. Such differences in the completeness of reporting can compromise the accuracy of the study results.
Studies called cohort studies, on the other hand, are much more likely to provide accurate results on the topic of abortion because they tend to gather sensitive information before women are diagnosed with breast cancer. And the results from cohort studies looking at this topic clearly show that abortion does not increase the risk of breast cancer [253,256-265].
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For a summary of research studies on abortion and breast cancer, please visit the Breast Cancer Research section. |
Electromagnetic Fields (EMF)
Exposure to EMF is one of many proposed environmental risk factors for breast cancer. To date, however, there is very little evidence that regular exposure to things like power lines and electric blankets increases the risk of breast cancer. While a few case-control studies have suggested a link [266], the main body of evidence, including larger prospective cohort studies, has not [267-273]. Taken together, the evidence does not support a link between EMF and breast cancer.
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For a summary of research studies on electromagnetic fields and breast cancer, please visit the Breast Cancer Research section. |
Blood Organochlorine Levels (exposure to certain types of pesticides and industrial chemicals)
Environmental pollutants have long been proposed as potential causes of breast cancer. Many of these compounds share structural similarities to estrogens, hence providing a theory for increasing breast cancer risk. Some of the most common and well-studied environmental pollutants are the organochlorines, which include the pesticide, DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), and industrial chemicals, such as PCB’s (polychlorinated biphenyls). One good way to assess exposure to such chemicals is by looking at their levels in a person’s blood. The results of most studies looking at the relationship between blood organochlorine levels and risk of breast cancer, including the Long Island Breast Cancer Study, have found no relationship between the two [274-278].
The occasional identification of clusters (small geographic areas, such as a town or county, where rates of breast cancer are higher than the national average) continues to fuel interest in environmental causes of breast cancer, though. Examples of such clusters include Long Island, New York [276] and Marin County, California [279]. Despite the clusters, no definite environmental contaminants that cause breast cancer have been identified. While this does not mean that there are no environmental pollutants that can increase risk of breast cancer, most of the clusters have been explained by differences in standard breast cancer risk factors, such as ages at menarche and menopause and number of children.
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For a summary of research studies on environmental pollutants and breast cancer, please visit the Breast Cancer Research section. |
Breast implants
Although breast implants have been proposed as a potential risk factor for breast cancer, there is no evidence to date that either saline or silicone implants increase the risk of disease, and several studies have reported a lower risk of breast cancer among women with implants [281-286]. This appears most likely due to the characteristics of women who tend to choose breast implants, such as a lower body mass index, that put them at lower risk for the disease rather than the implants themselves [287].
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For a summary of research studies on breast implants and breast cancer, please visit the Breast Cancer Research section. |
Although not as well studied as the factors described above, based on the research to date, the following factors are not thought to be related to either an increase or a decrease in breast cancer risk.
Bras/Under-wire bras
Although there has been a great deal of discussion that wearing an under-wire bra, or a bra in general, might increase risk for breast cancer, such a link is not supported by the scientific evidence. There is no reasonable reason the two would be directly linked, and any observed association is likely due to other factors associated with wearing a bra. A 1991 case-control study found that premenopausal women who did not wear bras had a lower risk of breast cancer than women who did wear bras; however, the researchers concluded this link was likely due to factors related to bra usage rather than the bra itself [280]. The women in the study who did not wear a bra were more likely to be lean and have smaller breasts, which the authors concluded might account for the link [280]. Weight increases risk of postmenopausal breast cancer, and breast size is currently under study as a potential risk factor for disease.
Deodorant use
There have only been a small number of studies looking at the link between deodorant use and breast cancer. Research in this area was driven by concerns that chemicals found in deodorants might enter the skin in the underarm and cause changes in the cells of the breast that could lead to cancer. However, the evidence to date doesn't support a link between the two [288,289]. One recent study concluded that the relatively high proportion of breast cancer found in the area of the breast closest to the underarm appears to be due to this area simply having more tissue than other parts of the breast [290]. Although a link between deodorant and breast cancer appears unlikely, there are too few studies in this area to say for sure.
Plastics
There is no scientific evidence to support a link between using plastic items, such as drinking water from a plastic bottle, and the risk of breast cancer.
Stress
Although one large prospective study found a weak association between life events and breast cancer risk, overall the evidence does not support a link between stress and breast cancer [294-299].
Trauma to the breast
To date, there is no scientific evidence to support a link between trauma or injury to the breast and risk of breast cancer.
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