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Updated: 6:37 p.m. Sunday, June 12, 2011 | Posted: 12:24 p.m. Friday, June 10, 2011

Cool facts about sweat

Athletes need to replace fluids lost through sweat during exercise



It's June. It's hot. We're sweating.

And so we've consulted a few local experts to discuss our bodies' natural swamp cooling systems, which draw water from the bloodstream and pump it to our skin's surface to keep us cool when it starts to feel like we're living in a furnace. Which we will be, for the next four months.

What is sweat?

Sweat is mostly water, with salt (sodium chloride) and smaller amounts of various minerals.

Why do we sweat?

Sweating is the body's way of cooling itself. When sweat evaporates off your skin, body heat is reduced.

How many sweat glands do we have?

Humans have between 2 million and 5 million sweat glands. They're located all over our bodies, except inside our ear canals and on our lips and genitals. They're most concentrated on the bottom of our feet and least concentrated on our backs.

Why does sweat stink?

Sweat itself is odorless. It's the bacteria on the skin that mix with it and make it stink.

Is all sweat created equal?

No. Humans have two types of sweat glands. Eccrine sweat glands, which produce the watery kind of sweat, are found all over our bodies, including on the palms of our hands, the soles of our feet and on our foreheads. Apocrine sweat glands, which produce small amounts of thicker fluid, are found in the armpits and genital area.

What causes sweat?

Exercise, hot weather, anxiety or stress all cause people to sweat, according to the Mayo Clinic. Emotional sweating usually occurs on your face, armpits, palms or soles of your feet, and only after puberty. The amount you sweat and how it smells can be affected by mood, diet, drugs, hormones and medical conditions.

Do men and women sweat the same?

Men have slightly saltier sweat than women, says Ed Coyle, a professor at the University of Texas and director of the Human Performance Laboratory who has studied sweat (among other things) for the past 12 years. "On average, men have 18 percent more sodium in their sweat," Coyle says. "Men are also bigger and therefore they need to produce more sweat to cool themselves."

Champion perspirers

Coyle isn't naming names, but he's worked with some seriously sweaty subjects. Among the sweatiest? A few University of Texas football players and one female basketball player. Sweating rates depend partly on genetics.

How much do you sweat?

Try weighing yourself (naked) before and after an hour-long run to see how much you sweat. Be sure to account for any fluids you drank during the run, including them in your total fluid loss. For example, if you lost a pound (which has 16 ounces) and also drank 12 ounces of sports drink during the run, your total fluid loss is 28 ounces.

Sweat too much?

Excessive sweating, or hyperhidrosis, is fairly common - and in extreme cases socially debilitating. But there are treatments. Sweat glands, just like everything else in the skin, have nerves. "Botox blocks the signals of those nerves and paralyzes the sweat glands," says Dr. Steven Henry, a plastic surgeon at the Seton Institute of Reconstructive Plastic Surgery in Austin. A Botox injection in the armpit or on the palm can deactivate those sweat glands for three to eight months. For permanent relief, doctors can use liposuction techniques to scrape the undersurface of the skin and suck out the sweat glands.

Drink up

If you don't drink when you sweat, you could get dehydrated or overheat. That's why fluid replacement before, during and after exercise and activity is so crucial. If you lose a liter of sweat per hour (or 33.8 fluid ounces), you should drink a liter per hour to prevent dehydration. Signs of heat illness include paleness, muscle cramps, headache, dizziness, nausea, clammy skin, fatigue or a drop in blood pressure. If someone is suffering from heat illness, cool him down quickly. An ice bath or cold-water bath works well.

Heat acclimation

People who are fit sweat more readily than those who are not. After exposing your body to elevated temperatures and mild exercise for a few days, you'll start sweating earlier. If it takes eight or 10 minutes before you start to sweat when you're not in shape, it might take five or six minutes once you're conditioned.

Ease the sting

As people become more aerobically fit and better acclimated to heat, the concentration of sodium in sweat declines. Therefore, sweat dripping into the eyes is less "stingy" in heat-acclimated people.

Pass the salt, please

The faster somebody sweats, the saltier the sweat, because there's less time for the sodium to be reabsorbed. Sweat enough and it'll build up on your shirt and skin. And it's not all that different from what comes out of the salt shaker. 'There's sea salt and there's my salt,' UT professor Ed Coyle jokes.

Do dogs sweat?

Sort of, but not in the same way people sweat. Dogs do have sweat glands on the pads of their paws, but their primary method of cooling is panting. Moisture on their tongue and the lining of their lungs evaporates, cooling them off.

What about other animals?

A lot of mammals sweat, but only a few, including horses and humans, produce lots of sweat in order to cool off. Primates and horses have armpits that sweat like ours. (Horse-sized roll-on deodorant, anyone?)

Sources: Ed Coyle, the Human Performance Lab; Dr. Jason Reichenberg, dermatologist at the University of Texas Southwestern at the Seton Family of Hospitals; Dr. Steven Henry, surgeon at the Seton Institute of Reconstructive Plastic Surgery; Runners World magazine; Mayo Clinic; PLoS ONE, a peer-reviewed science journal.

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