The myth that sweat itself smells
Short answer: Fresh sweat hardly smells at all. The odour appears when bacteria on the skin break down substances in the sweat. That is why hygiene, the fabric you wear and how quickly it dries matter so much.
Sweat is almost odourless
The body has two main types of sweat gland. The most common ones are found all over the body and release a watery sweat that is mostly water and salt. It barely smells. In the armpits and groin there are other glands that release sweat containing more fats and proteins. That sweat is also almost odourless when it first appears. It is only when the bacteria on the skin get to work that the smell develops over time.
The bacteria do the work
Many bacteria live on the skin, and most are completely harmless. When they reach the substances in sweat, they break them down into smaller compounds with a sharp smell. That takes a while, which is why you rarely smell right after a short walk but more after several hours in the same clothes. Warmth and moisture give the bacteria good conditions, so a hot, damp layer against the skin speeds the process up.
Clothes hold on to the smell
The smell settles into clothes as well. Some synthetic materials hold on to the fats from sweat and can keep a lasting odour even after washing. Cellulose fibres such as cotton and viscose, including viscose from bamboo, absorb moisture and let it evaporate. That does not mean they never smell, but many people find them easier to get fresh again after a wash. See bamboo tank top for men.
Change and wash often enough
The simplest advice is to change the clothes closest to your body every day and after exercise. Underwear and socks should be washed after each wear. Do not leave sweaty clothes folded up in a bag, because that gives the bacteria peace to work. Hang them up to dry if they cannot be washed straight away, and wash them as soon as you can. See bamboo underwear for men.
Layers for cold days
You sweat in winter too, for example on a long walk in heavy clothes or when moving from the cold into a warm room. A base layer that moves moisture away from the skin keeps you both drier and warmer. Long underpants and a thin undershirt make a big difference when there are many layers on top. See bamboo long johns. Change the base layer if it gets damp, so you do not end up cold.
When it is more than ordinary sweat
It is completely normal to sweat and smell a little after exertion. If you suddenly sweat much more than usual, sweat at night for no reason or notice a new and strong odour, there may be other causes. In that case, talk to your doctor. Clothing and habits can help a great deal, but they do not replace a proper check with someone who can examine you.
Frequently asked questions
Does sweat smell on its own
Hardly. The smell appears when bacteria on the skin break down substances in the sweat.
Why does synthetic sportswear sometimes smell after washing
Some synthetic fibres hold on to fats from sweat, which can leave a lasting odour.
How often should underwear be washed
After every wear, and always after exercise.
