Reviewed by Robert Jasmer, MD; Assistant Professor of Medicine, University of California, San Francisco
Also covered by: CBS News
READING, England, March 1 - Underarm antiperspirants may contribute to the risk of breast cancer because they contain aluminum salts with metal ions that mimic the effect of estrogen.
Until recently, it was thought that such estrogen-mimicking substances were uniformly organic -- either phenolic or carbon ring structures -- but evidence is mounting that some metals can also binding to estrogen receptors, said Philippa Darbre, Ph.D., of the University of Reading.
The underarm connection arises from the fact that aluminum -- which, as aluminum salts, comprises up to 25% of some antiperspirants -- appears to be one of those estrogen-mimicking metals, Dr. Darbre noted in an online review article in the Journal of Applied Toxicology.
It joins a growing list of so-called "metalloestrogens," including antimony, arsenite, barium, cadmium, chromium, cobalt, copper, lead, mercury, nickel, selenite, tin, and vanadate.
Aluminum salts "form a major source of aluminum exposure in humans," Dr. Darbre said, but "the effects of widespread, long-term and increasing use of these cosmetics remain unknown."
Reasons for concern, she said, are:
The cosmetics are applied near the breast.
Aluminum salts are left on the skin, allowing continuous exposure and possible migration through the skin into underlying tissue.
The practice of shaving the armpits may damage the stratum corneum of the skin, allowing direct chemical access to underlying tissue.
Several studies in the past decade, she noted, have shown that aluminum salts can pass through intact mouse skin and human armpit skin.
"It is reasonable to question whether this aluminum could then influence breast cancer," Dr. Darbre said.
Other substances that mimic estrogen include:
Phytoestrogens, found in nature as organic components of plants.
Natural and synthetic steroidal estrogens used in contraceptive pills and hormone replacement therapy.
Xenoestrogens, man-made non-steroidal organic chemicals used in agricultural spraying, industrial processes, urban waste or consumer products. They include organochlorine pesticides, polychlorinated biphenyls, bisphenol A, phthalates, alkylphenols and parabens.
Many of those substances -- including parabens and phthalates, among others -- are already being used in bodycare cosmetics, Dr. Darbre said. "Now the aluminum salts can be added to the list," she said.
Also on the danger list is cadmium, which is known to accumulate in the body from low-level environmental exposure. It's also introduced into the body through cigarette smoking, she noted -- perhaps one reason why smoking is linked to an increased risk of breast cancer.
Dr. Darbre called for more research to see what happens when many of these chemicals act together, noting that most studies have looked at single agents, which alone may not reach high enough levels to have a measurable effect in a living person.
"Each of these agents on their own may not have a powerful effect, but we need to see what happens when a number of them act together," she said. "It could be that this would have a significant effect on diseases like breast cancer."