Millions of tiny sweat makers
Your skin has about 2 to 4 million sweat glands. Each one is a tiny coiled tube deep in the middle layer of your skin.
The tube runs up to a little opening on the surface called a pore. That's where sweat comes out.
Sweat glands are almost everywhere on your skin. They're packed closest together on your palms, the soles of your feet and your forehead.
How sweat cools you
When you run, play or sit in the hot sun, your body warms up. Your brain notices and tells your sweat glands to get to work.
Sweat spreads over your skin. As it dries, the water turns into an invisible gas and floats away. That's called evaporation (ee-vap-uh-RAY-shun), and it takes heat with it.
That's why a breeze feels so good when you're sweaty. Moving air helps sweat dry faster, so you cool down faster.
On sticky, muggy days, sweat dries slowly, so you can feel extra hot.
What's in sweat
Sweat is mostly water, with a little bit of salt mixed in. That's why it tastes salty if it drips onto your lips.
It also carries tiny amounts of other things your body doesn't need.
When you sweat a lot, you lose water and some salt, so your body needs a refill.
Why sweat can smell
Here's a surprise: fresh sweat has almost no smell at all.
Your skin is home to tiny living things called bacteria. Most of them are harmless. When they munch on sweat, they make the smell.
Armpits have a special kind of sweat gland, and they're warm and tucked away, so bacteria love it there. That's why armpits can get smelly when other spots don't.
Washing with soap and water and wearing clean clothes keeps the smell away.
Other reasons you sweat
You don't only sweat when you're hot. Feeling nervous or excited can make your hands, feet or forehead sweaty too.
Spicy food can make some people sweat, even when they aren't hot at all.
Sweating for any of these reasons is normal. It happens to everyone.
Drink up!
Sweating uses up water, so drink water before, during and after you play hard, especially on hot days.
If you feel very thirsty, tired or dizzy in the heat, stop playing. Find shade, sip water and tell a grown-up.