Scientists believe aluminum salts found in antiperspirants could heighten breast cancer risk, but they caution that this theory requires further investigation.

According to the authors of a review in the April issue of the Journal of Applied Toxicology, chemicals that mimic the body's natural hormone estrogen are known to affect breast cancer risk. And there's increasing evidence that aluminum salts, which account for 25 percent of the volume of some antiperspirants, can get through the skin and into the body, where they can mimic estrogen.

"Since estrogen is known to be involved in the development and progression of human breast cancer, any components of the environment that have estrogenic activity and which can enter the human breast could theoretically influence a woman's risk of breast cancer," article author Dr. Philippa Darbre, of the School of Biological Sciences at the University of Reading in the U.K., said in a prepared statement.

Since antiperspirants are sprayed into the armpits, exposure to aluminum salts is concentrated near the breasts. Furthermore, women often apply antiperspirants immediately after shaving their armpits, which means the skin there is likely to be damaged and less able to keep out the aluminum salts.

"It is reasonable to question whether this aluminum could then influence breast cancer," Darbre said.

Aluminum salts in antiperspirants aren't the only concern, she noted. Smoking tobacco introduces the element cadmium into the body, and cadmium can collect in breast tissue. Cadmium can bind to estrogen receptors and influence their action. There is evidence that the accumulation of cadmium can increase breast cancer risk.

"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 -- it could be that this would have a significant effect on diseases like breast cancer," Darbre said.