How Sweat Works

Photo by Casarsa / iStock

Extreme heat is everywhere this week. And, July was the hottest month ever recorded, according to the National Oceanic and Atmospheric Administration. ICYMI, here’s our previously published post on perspiration and how to cope with it. 

WARM WEATHER brings the sweet fragrance of flowering trees and the mouth-watering smells of barbecue along with the less-appealing scents of sweaty body odor.  Sweat is the body’s response to excess heat, whether from the sun, exercise, fever, menopause or some combination of these.  Of the 2- million-plus sweat glands right under most people’s skin, women have more, but men’s sweat smells worse.  How to deal with it depends on whether you want to combat the odor, skip the wet altogether or prefer doing nothing at all.

Animals pant to rid their bodies of excess heat by way of their mouths.  But humans sweat from glands, transferring heat from our entire body surface. Of the two kinds of human sweat glands, eccrine glands are spread over the body, and they produce a mixture of minerals that differ depending on the person.  If your sweat stings your eyes, you are a salty sweater.

But the strongest smells come from sweat produced by apocrine glands, located under the arms, around the breasts and in the groin.  Some of these odors are pheromones, the “personal scent” that attracts the opposite sex, which many people find unpleasant.  Even worse are odors from the sweat that’s caused by stress, which is chemically different from sweat from heat or exercise.

Sweat from the apocrine glands contains small amounts of fatty acids, which are very tasty to the main culprit of bad odors: the bacteria that live on your skin.  Bacteria gobble up sweat and then you stink. Diet also plays a role: After a night of too much pasta aglio e olio and red wine, excess morning-after sweat comes with strong eau de garlic.  Red meat, curry and onions also make the odor worse.

Many deodorants simply cover up bad odors with good scents, such as tuberose. Most deodorants are labeled for either men or women, and although manufacturers often use exactly the same ingredients for both, unisex deodorants make up as little as 10 percent of the market.

Some deodorants also disinfect the armpit with an alcohol base that makes the skin slightly acidic and thus less attractive to bacteria.  Others contain a specific ingredient, most often triclosan, that inhibits the growth of bacteria and other microbes on the skin.  (Deodorant soaps often contain triclosan, but studies have found no benefits from antibacterial soaps, either for preventing infection or for reducing bacteria.)

To combat the drip, antiperspirants have a different function: to stop sweat and thus odor by clogging the pores or ducts through which sweat pours.  Most antiperspirants use some version of aluminum—lately, aluminum zirconium compounds that are less likely to cause irritation than earlier forms.  Because antiperspirants alter a bodily function, unlike deodorants, they are subject to FDA regulations.  To boast “all day protection” requires only that the brand reduce sweat by 20 percent; and for “extra strength,” only by 30 percent.  Many antiperspirants contain deodorants.

You might be one of the lucky people whose sweat doesn’t smell at all.  Alternatively, you could suffer from hyperhidrosis, excessive sweating and find antiperspirants a necessity.

While the aluminum in antiperspirants was once suspected of contributing to risks for breast cancer and Alzheimer’s disease, studies have failed to support both hypotheses.  Research, however, has not solved the problem of why one person’s antiperspirant seems to lose its effectiveness after about six months, at which point brands must be switched.  Neither does anyone understand what causes the yellow staining on clothes, but manufacturers are studying the “yellowing phenomenon.”

To avoid the side effects of commercial antiperspirants, from skin irritation to yellowing, alternatives can be made using various plant oils and extracts that have antibacterial powers, including white thyme essential oil, rosemary essential oil, lavender essential oil and castor oil.

Also low tech, wearing natural fabrics, which breathe more easily, reduces sweating.  Wicking fabrics may soak up some of the sweat, but the remaining moisture and its accompanying bacteria always seem to smell worse.  Try wearing several light natural-fabric layers instead.

In extreme cases, there is Botox, which paralyzes and shrinks the sweat glands by blocking a neurotransmitter that stimulates them.  Most often used for those with hyperhidrosis, Botox is also popular with brides, grooms and prom-goers who want to avoid embarrassment as well as ruining expensive clothes.  Several injections in the armpits can last up to eight months.

So you can join the Americans who spend billions per year on deodorants and antiperspirants. Or head in the other direction, toward saunas and sweat lodges, and enjoy a good sweat—even if the overpowering smell is garlic.

—Mary Carpenter

Well-Being Editor Mary Carpenter reports on news you can use right here every Tuesday.