The FDA is mainly concerned about claims being made for a product, Holman says. For example, in the familiar slogan, "strong enough for a man but made for a woman," the company had to prove that the product was tested in both men and women because there are physiological differences between them. Similarly, testing must confirm marketing statements such as "so effective you could skip a day."

By contrast, Holman says that if a company claimed that a new antiperspirant ingredient is effective, "it would require a new drug application because the ingredient is not already included in the antiperspirant monograph as generally recognized as safe and effective."

Holman also says that manufacturers tend to test antiperspirant products on more women than men. One reason seems to be underarm hair. Women are required to shave two days before testing to keep hair to a minimum and to minimize skin irritation. "With that said, skin irritation related to shaving is not a major safety concern because it is not serious or life threatening," Holman says. "And common sense dictates women will not keep using a particular product if it causes irritation."

The important thing to remember, says Holman, "is that antiperspirants don't completely eliminate sweat." According to the FDA's testing standards, the most effective products, those that claim "extra strength" or "maximum strength," are based on at least a 30 percent sweat reduction rate in most people. Regular strength products test at a 20 percent sweat reduction rate in most people.

Sweating Too Much, or Not Enough

If the complex biological mechanism of perspiration goes awry, it can result in either excessive perspiration (hyperhidrosis) or little or no perspiration (anhidrosis), a potentially life-threatening condition.

Dermatologists at the AAD say that excessive sweating is normal when a person is anxious or has a fever. However, excessive sweating can be a chronic condition and may signal other medical conditions such as thyroid problems, low blood sugar levels, a nervous system disorder, or the onset of menopause.

Excessive sweating is more than a mild nuisance that some people experience. According to the AAD, hyperhidrosis affects about 8 million Americans. Depending on where it occurs on the body, hyperhidrosis has several treatment options, including topical agents such as prescription antiperspirants, oral medications, and surgery. Prescription antiperspirants contain higher doses of the active ingredient aluminum chloride. Skin irritation is the main side effect with prescription antiperspirants such as Drysol (aluminum chloride hexahydrate).

In July 2004, the FDA approved Botox (botulinum toxin type A), a drug that is used to temporarily erase wrinkles for cosmetic purposes, to treat severe underarm sweating (primary axillary hyperhidrosis) that cannot be managed by topical agents. Available by prescription only, botulinum toxin type A is a protein produced by the bacterium Clostridium botulinum. This protein works by interrupting the chemical messages released by nerve endings that tell the sweat gland when to sweat.

Administered into the armpit, small doses of an injectable form of the sterile purified botulinum toxin stop release of the chemical messenger acetylcholine that supplies nerves to the eccrine glands, thereby temporarily paralyzing the nerves in the underarm that stimulate sweat production.

To avoid the possibility that Botox treatments can mask a potentially serious disease, the FDA advises patients to be evaluated by a doctor for other possible causes of excessive sweating. Botox is approved for treatment of the underarms, but not for excessive sweating of other sites such as the feet and palms.

The Cancer Myth

The rise of the Internet has made it easy for false health claims, scary stories, and rumors to reach millions of people in a matter of minutes. One such myth says that antiperspirants may cause breast cancer.

According to the National Cancer Institute (NCI), the breast cancer-antiperspirant myth first appeared in the form of an e-mail in the 1990s, and continues to resurface and recirculate about every year or so. The false information suggests that antiperspirants contain harmful substances, which can be absorbed through the skin or can enter the body near the breasts through nicks in the skin caused by shaving. The e-mails also suggested that antiperspirants keep a person from "sweating out toxins," resulting in the spread of cancer-causing toxins via the lymph nodes.

But the NCI says that no existing scientific or medical evidence links the use of underarm antiperspirants or deodorants to the subsequent development of breast cancer. The FDA, the Mayo Clinic, the American Cancer Society (ACS), and the Cosmetic, Toiletry and Fragrance Association agree. Razor nicks may increase the risk of skin infection, but not cancer.

According to the ACS, sweat glands are not connected to the lymph nodes. Most cancer-causing substances are removed by the kidneys, are released through urine or by the liver, and are eliminated with feces. The ACS says that lymph nodes may help to clear some toxins from the body, but they do not release these toxins through sweating. Sweat is not a significant route for eliminating toxins from the body.

And a study of 813 women with breast cancer and 703 women with no history of breast cancer, published in the October 2002 issue of the Journal of the National Cancer Institute, found that antiperspirants do not cause breast cancer.

Some speculate that the myth could have been started by women being told not to wear antiperspirants or deodorants before a mammogram. They were told this, not for safety reasons, but because residue from these products appearing in the X-ray is often mistaken for an abnormality in the breast.

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About the Author

FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.