For some, the thought of abandoning antiperspirants gives them the cold sweats. For others, it's the thought of using them. Underarm antiperspirants guard against odor and wetness, but could the aluminum-based compounds that reduce sweat actually cause Alzheimer's disease and breast cancer?

The antiperspirant finger-pointing began more than 40 years ago with new discoveries about Alzheimer's, a progressive dementia that affects more than five million Americans. Antiperspirants use compounds—such as aluminum chloride, aluminum chlorohydrate and aluminum zirconium—to form a temporary sweat duct plug. Researchers back then found that exposure to aluminum caused rabbits' brains to develop nerve cell damage—thought to be a precursor to Alzheimer's at the time—and long-term dialysis patients with high levels of the metal developed dementia.

Critics charge that rabbits are not good animal models for human brain diseases and note that the dialysis patients suffered from dialysis encephalopathy, or "dialysis dementia," not Alzheimer's disease. But neuropathologist Daniel P. Perl at Mount Sinai Medical Center in New York City has found evidence of aluminum in the neurofibrillary tangles that characterize Alzheimer's disease.

"Just because the rabbit is not a good model doesn't mean that there is not a problem," he says. "There are a zillion examples of things that are clearly toxic to humans, but when exposed to rats—even monkeys—show no problem."

On average, most people take in approximately 30 to 50 milligrams per day of aluminum from food; those using over-the-counter medications such as antacids and buffered aspirins ingest larger amounts, roughly five grams a day. At that level, there is little evidence of harm, most experts say.

Skeptics cite such a lack of epidemiologic evidence in the decades since the concern was first raised and say avoiding the third most common element in Earth's crust is impossible. Even if people were to ban aluminum pots and pans, chuck soda cans or cap antiperspirants, the ubiquitous metal would still be in the food they eat, the water they drink and, sometimes, even in the air they breathe.

"Everyone's been exposed, which makes it very difficult to study," says epidemiologist Amy Borenstein of the College of Public Health at the University of South Florida in Tampa. Her 1990 case-control study, reported in the Journal of Clinical Epidemiology, found no association between aluminum-containing products and Alzheimer's disease. "If it even plays a role at all," she says, "it's negligible."

William Thies, vice president of medical and scientific relations at the Alzheimer's Association in Chicago, calls the notion that antiperspirants could cause Alzheimer's disease an old legend. "One of the things that happens in Alzheimer's brains is that they shrink," he says. "So, you have accumulated a certain amount of aluminum in your brain, and as your brain shrinks, the concentration is going to appear high."

Cancer has also been a source of concern for some, which may have originated with instructions that women avoid antiperspirants, deodorants, powders and lotions before mammograms in order to avoid confusing shadows on X-rays. This may have led to confusion about a potential link between cancer and personal care products.

Adding to uncertainty, in the 1990s an anonymous e-mail chain letter warned that antiperspirants caused breast cancer. Ted Gansler, director of medical content at the American Cancer Society in Atlanta, says that in the past seven years, his organization has received thousands of e-mails and phone calls in response to this chain letter.

The letter claims that inhibiting perspiration causes harmful substances to be trapped in the body where they form cancer. But sweat is mostly electrolytes and water, Gansler says, and sweating is not a significant mechanism for expelling unwanted compounds, more commonly eliminated in urine and feces. "It would be nice if as many people as [those who] forwarded the e-mail about antiperspirants, urged their friends and relatives to get a mammogram every year starting at age 40," he says. "We would have saved a lot more lives."

The idea that toxics would enter the body through the underarm, migrate to the lymph nodes and then travel to the breast may have more to do with geography than biology. "Why you would think that antiperspirant would somehow go upstream and get into your lymph nodes and then somehow get into the breast is unclear," says Timothy Moynihan, education chair and consultant for the division of medical oncology at the Mayo Clinic in Rochester, Minn. "It doesn't make sense other than the fact that it's in the neighborhood."

Ultimately, lifestyle changes like exercising are more important than whether or not your underarms are sweaty while you are walking around or working out. "Everyone worries about underarm antiperspirants," Moynihan adds, "but nobody quits smoking."