The Biology of Sweat

Any woman who's ever reached for a glass of wine on a date only to reveal the soaked underarms of her outfit has probably wished she could remove her sweat glands. But long before pit stains became a social obstacle, perspiring was crucial to survival. "Sweat cooled off our ancestors in the grasslands of Africa," says anthropologist Helen Fisher, Ph.D. "It allowed them to hunt and forage without sweltering."

But a hot climate isn't the only thing that makes us sweat. Nerve-racking situations (e.g., a big job interview) can prompt the brain to trigger the release of stress hormones that raise your body's temperature enough to warrant a cooldown.

The Basic Biology


Bodily functions such as digestion and muscle movements generate heat, and we perspire constantly to keep things chilled. So while you're busy patting down your sweat 'stache, your system is on AC overdrive, sending and fielding a complex network of cool-down codes. Here's what's happening in your body:

  1. In response to scorching temps or frazzled nerves, your brain fires a sweat signal down your spinal cord, triggering the release of a chemical called acetylcholine.
  2. The acetylcholine shoots from your spinal cord into thousands of nerves that travel to your legs, arms, chest, face, and back.
  3. The acetylcholine arrives at your 4 million eccrine glands (wedged between your fat and skin layers) and prompts them to start filtering fluid from your bloodstream to produce sweat.
  4. Your eccrine glands then pump out the stuff—99 percent water, 1 percent salt—through your skin's millions of pores.
  5. The released sweat helps regulate your core temperature, much like splashing yourself with cold water helps you cool off. Most sweat starts to evaporate immediately, but if your glands are working overtime, it'll pool up on your skin. Or, if you're dressed, it'll seep into your clothes.

Ways to Stay Dry

Even people who think they're as dry as a desert are constantly losing water, says Dee Anna Glaser, M.D., a professor of dermatology at Saint Louis University School of Medicine. "Just the act of breathing makes us sweat." On average, we perspire enough each day to fill a shot glass (1.5 ounces), and that's before working out or otherwise exerting ourselves. Because the highest concentrations of sweat glands are in our armpits, forehead, soles, palms, and scalp, those tend to be our dampest parts. If you're a real drippy mess, you can thank Mom and Dad; DNA regulates the actual amount we sweat, says Glaser.

Swiping on antiperspirant is the easiest way to stay dry. Most formulas contain aluminum, which soaks into your skin and corks your eccrine glands. (Plain odor-masking traditional or natural deodorants, on the other hand, contain no aluminum and therefore no sweat blockers.) Technically, you can use antiperspirant anywhere, but because many are oil based, they're hard to apply to, say, your hands or feet. Hint: Applying antiperspirant to your sweat-free pits in the p.m. can make it more effective, says Kelley Redbord, M.D., a dermatologist in Vienna, Virginia. "Because your skin is dry and you're not as physically active at night, it's easier for antiperspirant to plug your glands for up to three days," she says. Just be wary of using it morning and night; too many swipes may cause skin irritation.

Still sweating? Try a clinical-strength over-the-counter antiperspirant; these are packed with up to 20 percent aluminum zirconium, the maximum amount allowed by the FDA. (While some scientists point to a potential link between aluminum and breast cancer, the American Cancer Society maintains that there's no solid evidence to support this claim.) Or order a box of MedeTate wipes ($48 for a pack of 30, dermadoctor.com). The mix of a type of aluminum zirconium and acetylcholine-hindering botanicals on these towelettes isn't long lasting, but it does work well in a pinch.

If no other solution is effective enough, you can safely turn to—wait for it—Botox. The much-hyped wrinkle reducer has been approved by the FDA to combat underarm sweat (it works by binding to and blocking acetylcholine). When Botox is injected into the forehead, palms, armpits, or feet, it stops seepage for as long as eight months. At around $800 a vial (and that's just enough for both armpits), the treatment doesn't come cheap, but it also won't divert your sweat anywhere else.

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