Cancer experts are up in arms over two recent studies linking deodorant use to breast cancer, saying conclusions from the studies are flawed.
An e-mail hoax in the 1990s suggested that chemicals in antiperspirants can cause breast cancer, and quickly became a powerful urban legend. In 2002, a study of 1,600 women found that deodorant use—with or without shaving—is not associated with breast cancer. But deodorants continue to be linked to breast cancer at least in part because environmental factors contribute to risk, says Patrick Borgen, chief of breast cancer surgery at New York's Memorial Sloan Kettering Cancer Center.
Based on data from 437 breast cancer survivors, lead researcher Kris McGrath in December reported that women who used deodorant at least twice a week and shaved more than three times a week were diagnosed with breast cancer nearly 15 years earlier than those who did not shave or use antiperspirants (Eur. J. Cancer Prev. 12, 479–485; 2003).
One possible explanation is that aluminum salts in deodorants can enter shaven skin and alter DNA, says McGrath, section chief of Allergy and Immunology at St. Joseph Hospital in Chicago. Animal studies show that aluminum can travel through the body and appear in the brain and in breast milk, he adds.
Data from animals can help build a hypothesis, but cannot be used as proof unless they are also observed in humans, notes Wendy Chen, an oncologist and epidemiologist at Harvard Medical School. The study has other limitations, such as a small sample size and a lack of proper controls, Chen says. By not including women who never had breast cancer, she adds, all the study shows is that women who use a lot of deodorant happen to be younger.
“This study seems particularly weak,” says Michael Thun, head of epidemiological research at the American Cancer Society. “The analysis doesn't control for [body mass index], use of postmenopausal hormones and the age of first live birth, just for starters.”
The second study, published in January, reported that preservatives called parabens, known to mimic estrogen, were also found in breast tumors (J. Appl. Toxicol. 24, 5–13; 2004). But animal studies suggest parabens would have to be about 500 to 10,000 times more potent to equal oral estrogen.
The mere presence of parabens in tumors does not mean anything, says Borgen. Because breast tumors are highly vascular, he says, they are likely to have traces of everything in the bloodstream. “If I put blue dye into a vein in a foot and took a breast tumor out, it would be blue,” Borgen says. “No one would think blue dye caused the cancer.”
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Surendran, A. Studies linking breast cancer to deodorants smell rotten, experts say. Nat Med 10, 216 (2004). https://doi.org/10.1038/nm0304-216b