|Sweaty arm by Minghong, Wikimedia|
Sweat comes from glands in the dermis of your skin. The apocrine glands respond to stress. The eccrine glands help regulate body temperature.
Why does it smell? Though some odor is associated with apocrine sweat glands, which are found predominantly in the armpit and groin, sweat odor generally comes from bacterial growth
What is sweat made of? Sweat is mostly water, but it also contains waste products (like ammonia), salts, and sugar. Urea, which is what gives urine its yellow color, is an ammonia-containing chemical that is also sometimes found in sweat.
Fancy term for this: perspiration
Why do we sweat? Because we need to regulate our body temperature! As the sweat evaporates it takes heat away from the skin and cools your body down. Sweat is also one way to excrete excess toxins (i.e. ammonia, which is obtained from the breakdown of proteins) from the body.