Suggest Remedy For Rashes On The Back Of Both Hands

I have tiny red dot rash on the back of both of my hands. I've noticed that I get them in hot weather, and usually start on my right hand, then on my left hand. It usually starts with two or three bumps, and spreads to both hands by the 2nd and 3rd days. Some of them join up to make a larger cluster if I scratch them. They only sting/and/itch sometimes.