Humans are born with between 2 million and 4 million sweat glands located all over our bodies — except in a few places, like the lips, nails, nipples, eyeballs, and ear canals.

Sweating is triggered by various things: physical activity, being in a hot place, emotions, fever, hormones, pregnancy, toxins, and food. Sweating because of the heat, sweating due to exercise, and sweating from stress are all slightly chemically different.

Sweat itself is a clear, odorless liquid made of water, salt, proteins, and oils. However, there are two different types of sweat glands.

Eccrine glands, which are located all over the body, produce sweat that cools the skin through evaporation. This type of sweat is 99% water combined with trace amounts of potassium, chloride, and sodium.

Apocrine glands, dormant until puberty, are located only in the hairier parts of the body: armpit, groin, and scalp. This kind of sweat is thicker (and smellier) because it contains fatty acids and proteins that provide a feast for the bacteria that live on the skin. The bacteria break it down into a by-product called propionic acid, which comes from the same family as ordinary vinegar. However, these microbes are not all bad because they protect the skin from invading germs.

Some factors can affect the smell of sweat, including humidity, caffeine, nicotine, alcohol, and various medications. Diet also contributes to the odor, particularly things like onions, curry, cumin, garlic, fatty foods, and red meat.    Spicy hot foods irritate the nerves leading to the sweat glands, activating them. Sportswear is often made from synthetics such as Lycra or polyester, materials that wick away sweat but tend to retain body odor.

For sweat to cool us down, it must evaporate; humidity makes it more difficult. Thus, the sayings, “It’s not the heat; it’s the humidity!” and “At least it’s a DRY heat!”

When water evaporates from the skin, turning from a liquid into a gas, it removes heat from the blood. Cooler blood travels around the body, keeping organs the correct temperature.

Sweat glands are coiled loops just below the skin’s surface, leading to a duct, which lead to the pores. The sweat is water pulled from the blood and surrounding tissues. The more you sweat, the saltier the sweat; the less you sweat, the less salty. This is because the longer the liquid remains in the coil, the more time the body has to reabsorb the potassium, chloride, and sodium. If you’re sweating up a storm, there isn’t enough time to do that, as the sweat moves through the coil quickly. This is why the skin tastes saltier the more you sweat. Sports drinks like Gatorade are formulated to replace the salts lost due to heavy sweating.

We are born with all the sweat glands that we will ever have. It takes about two years after birth for sweat glands to mature. Babies are less able to regulate their body temperature than adults, and are more susceptible to heat.

Babies born and raised in warm climates develop more active sweat glands than those born in cool climates. If you move to a hotter climate than you’re accustomed to, your ability to sweat increases in about six weeks.

People of East Asian descent often have a particular gene that makes their sweat less odiferous than others.

There are not very many species of animal that sweat. Humans have ten times more sweat glands than chimpanzees, who mainly sweat from their armpits. A thick layer of hair prevents the rapid evaporation than a human’s thin layer of hair promotes.

The ability to stay cool gave early humans an edge, allowing them to hunt in the heat of the day when other animals were forced to stay in the shade. Sweat endowed humans with the ability to run long distances at a sustained pace, a talent few other animals have.

Horses, donkeys, and zebras sweat. Cows sweat through their noses; cats and dogs sweat between the pads on their paws. Hippo sweat is red, resembling blood, because it’s laden with antiseptics and sunscreen. The phrase “sweating like a pig” doesn’t make much sense because pigs have few sweat glands. The saying may come from the process of smelting a type of iron called “pig iron.”


Can you detox your body by sweating up a storm? No, not really. Sweat glands are capable of excreting some toxins, but they do that naturally in a process that can’t be controlled or influenced.

Do you need to take salt supplements while sweating? Only if you’re drinking a lot of water, like running a marathon in a desert on a hot day, or hiking up from the bottom of the Grand Canyon. The body is in a perpetual balance of water and salt, so drinking large amounts of water in a short time can throw the balance off.

Can you lose weight by sweating? Only temporarily. After you finish that workout or step out of the sauna, the weight will return once you have a drink. During intense exercise, athletes sometimes sweat off 2 to 6% of their body weight. That amounts to 9 pounds (4 kg) for a 150-pound (68 kg) person.

Why do we sweat when nervous? It’s related to the fight-or-flight response. If you suddenly see a lion stalking you, the adrenaline triggers the sweat glands to cover your skin with liquid, preparing you for fighting or fleeing by cooling you down.

A human in a hot situation can sweat a quart per hour. The human body can absorb and replace two quarts of water per hour.

The more fit you are, the quicker your body will begin to sweat due to conditioning. This allows you to continue to exercise longer.

Larger people sweat more than smaller people, not only because they have to work harder to move around, but also because they have more surface area to cool.

Old people sweat less than young people.

Women have slightly more sweat glands than men, but men produce more sweat. When men and women drank the same amount of fluid during exercise, the women’s sweat rate was 0.57 quarts per hour, while the men’s sweat rate was 1.12 quarts per hour. Why do women sweat less? It’s likely because they tend to be smaller and have less surface area to cover.

The chemical composition of sweat between men and women is discernably different.

Men have more apocrine sweat glands than women do.

In a blind “sniff test” women were asked to rank the scent of males from most attractive to least. They tended to prefer the smell of whatever man whose genes were most unlike their own. This indicates that women are most attracted to a potential mate most likely to ensure a robust immune system for offspring.

The typical human sweats about 278 gallons (1,052 l) annually.

The hand, feet, and head have the most sweat glands; the back and butt have the least.

Although inner ear canals do not sweat, a modified sweat gland produces ear wax.

A single sweat gland produces about one 10-billionth of a quart of sweat per minute. At that rate it would take one gland around five weeks working around the clock to fill a teaspoon.