Sweating might feel annoying or embarrassing, but it’s one of your body’s smartest survival tools: Whether you’re dripping through a workout or suddenly sweating during a stressful meeting, perspiration is the main way our bodies regulate their temperature. To do so, millions of sweat glands expel mostly water, which is mixed with small amounts of other substances, such as sodium and chloride. Exactly how much you sweat varies based on genetics, fitness level, climate, and age. But sweat can also offer clues about hydration, stress, hormones, medication side effects, and overall health. Here’s what your sweat could be trying to tell you.