The sole purpose of sweat is to cool the body down. As your core temperature rises above 98.6 degrees, your brain signals to the sweat glands to increase production; and when sweat appears on your skin, it’s evaporated into the air, taking body heat with it. Your sweat rate is determined by two primary factors: the environment (how hot it is) and your individual response to heat. “Someone who is acclimated to heat and working out in a hotter environment is generally not going to sweat as much as someone new to it,” says Walt Thompson, Ph.D., president of the American College of Sports Medicine and an associate dean at Georgia State University in Atlanta.