Why do people sweat when exercising?

To cool yourself. sweat is like water just saltier, but that doesn't mean it doesn't have the coolness of water. so sweat is there to cool you when you don't have water

Sweating is about temperature control when you are hot you sweat more to cool down or to level out your temperature.  

Because it is under the health section, i would say chemo but idk much. i'm pretty sure it's either a machine or a pill. sorry if i am wrong