How to Keep Your Cool
For: When Sweating Doesn’t Stop, August 2003
Americans spend huge sums on antiperspirants and tend to see sweating as sloppy or unclean. Many would gladly take a pill that prevented perspiration altogether. But such a pill would be deadly, since sweating’s primary—and crucial—function is to cool the body. When sweat evaporates, heat is removed.
You perspire when your body’s temperature rises, and also in response to emotional stimuli such as anxiety, fear, or sexual arousal, or even spicy food. Millions of sweat glands pump the fluid, which comes primarily from the blood, up through ducts to the surface of the skin. The heat-regulating function appears to be limited to so-called eccrine sweat glands, located all over the body, but especially in the feet and palms.
Apocrine sweat glands, the other major type, respond to emotional and nervous stimuli. Connected to hair follicles, they are located mostly in the armpits, groin, and around the navel. In mammals, apocrine perspiration helps attract a mate through scent, but that doesn’t seem to be true of humans today.
What is sweat?
It’s mainly water, with small amounts of sodium chloride, potassium, and other minerals (known as electrolytes) that play an important role in regulating blood pressure and the body’s water balance. Sweat from apocrine glands is different, however, and gives sweating a bad name. It contains proteins and fatty acids, and it mixes with oil and dirt, making it thicker and slightly yellowish. "Body odor" comes from bacteria feeding on organic particles in this kind of sweat.
How much do people sweat?
Sweat rates vary greatly, depending partly on genetics. Sedentary people may sweat anywhere from a negligible amount to two quarts a day. Under extreme conditions, heat and physical exertion can increase the output to as much as two quarts an hour. Factors such as age, race, sex, and conditioning affect the amount a person sweats.
Why do you sweat more when you exercise?
Your working muscles burn lots of calories and thus produce heat, which raises body temperature. The body reacts by increasing blood flow to the skin, which helps remove heat (this is called convection), and by sweating more. It’s the evaporation of sweat that cools you off.
Do you sweat more when it’s humid?
Yes, but it doesn’t cool you off, since the sweat doesn’t evaporate much and simply drips off. That’s why a hot, humid climate feels more uncomfortable than a hotter but drier climate. Toweling off when sweating won’t help much. Air movement does promote evaporation of sweat, so a fan may help.
Why does sweating make you thirsty?
Sweating reduces blood volume and boosts the concentration of sodium in the blood, which stimulates the brain to trigger thirst. But when you exercise or work hard, the thirst mechanism doesn’t keep up with your need for fluid. By the time you’re thirsty, you’ve already lost a lot of fluid. A fluid deficit of even a pint or two can impair physical performance. Always drink before, during, and after exercising.
Why is dehydration a problem?
When you don’t replace water lost through perspiration, blood volume drops, you sweat less, and body temperature rises. This can hurt performance and lead to heat exhaustion or heat stroke (characterized by body temperature of 104° or higher and often severe headache, rapid pulse, and possibly loss of consciousness). In addition, you can lose excessive amounts of sodium during severe and prolonged sweating—for instance, during a marathon in hot weather—which can also impair performance. Sports drinks or salty snacks can provide some sodium during endurance exercise. In the long term, your normal diet will replace the minerals lost in sweat.
Is sweating a lot a sign of fitness?
It depends. If you become physically fit, your core temperature will rise more slowly, your heart will beat more slowly at a given workload, and you’ll be a more efficient sweater—for instance, you’ll start to sweat at a lower core body temperature and sweat more. Thus you stay cooler and can exercise more in the heat. Your sweat contains less sodium and other minerals (though this varies from person to person). Just as exercise increases efficiency and size of muscles, it boosts the efficiency of the heat-regulation system and even the size of sweat glands. But it’s a confusing question: sedentary people usually sweat a lot because they deal poorly with the heat—their core temperature rises faster, the heart beats faster, and they sweat more at a given workload than well-conditioned people, and thus they become more fatigued.
Do you get used to the heat?
Yes. Changes in your cardiovascular and nervous systems (such as a lower heart rate and increased blood flow to the skin) help you acclimatize to hotter weather. Your sweat glands become bigger. Most of the adaptation occurs during the first five days, but full acclimatization takes about two weeks. The fitter you are, and the more you exercise in the heat, the faster you’ll be able to acclimatize.
Do women tolerate heat less well then men?
It used to be thought so, but studies show that women and men who are equally fit cope equally well. Cardiovascular fitness is the most important factor in heat tolerance. One difference between the sexes is that men, on average, sweat more than women, so they may deal a little better with dry heat. The menstrual cycle does not affect heat tolerance in women. At the outset of menopause, however, many women experience hot flashes—sudden bouts of flushing and perspiration.
Why do older people have such a problem when there’s a heat wave?
Usually because their cardiovascular system is less fit—so they tend to pump less blood to the skin (but with a greater strain on the heart), sweat less, and thus are less able to dissipate internal heat. Coping with the heat can seriously tax the heart of anyone who is not healthy and fit. In addition, older people can easily become dehydrated because they tend to become less thirsty—so they should make a special effort to drink plenty of fluids. Well-trained older athletes, however, do cope well with the heat.
UC Berkeley Wellness Letter, August 2001