Factors with Controversial, or Unproven Effect on Breast Cancer Risk
Antiperspirants: Internet e-mail rumors have suggested that chemicals in underarm antiperspirants are absorbed through the skin, interfere with lymph circulation, and cause toxins to build up in the breast and eventually lead to breast cancer. There is no experimental or epidemiological evidence to support this rumor. Chemicals in products such as antiperspirants are tested thoroughly to ensure their safety. The claims about toxin buildup are not supported by the scientific basis of carcinogenesis (cancer formation).
Underwire bras: Internet e-mail rumors and at least one book have suggested that bras cause breast cancer by obstructing lymph flow. There is no scientific or clinical basis for that claim.
Smoking: Most studies on smoking and breast cancer risk have not found any association. There may be some increased risk after many years of heavy smoking. Nonetheless, studies have shown that smoking damages overall health and increases the risk of developing and dying from many other cancers, as well as heart disease and stroke. Clearly, smoking should be avoided.
Induced abortion: Several studies have provided very strong data that induced abortions have no overall effect on the risk of breast cancer. Also, there is no evidence of a direct relationship between breast cancer and spontaneous abortion (miscarriage) in most of the studies that have been published. This, however, is still controversial, with some doctors believing that abortion does increase the risk of breast cancer.
Breast implants: Several studies have found that breast implants do not increase breast cancer risk although silicone breast implants can cause scar tissue to form in the breast. Implants do make it harder to see breast tissue on standard mammograms, but additional x-ray pictures called implant displacement views can be used to completely examine the breast tissue.
Night work: A few recent studies have suggested that women who work at night, for example, nurses on a night shift, have an increased risk of developing breast cancer. However, this increased risk has not yet been proven, and when further studies are conducted, this factor may be found to be unimportant.