No matter how good your antiperspirant is or how lightweight your workout clothes are, sweating while you work out is just about as inevitable as death and taxes. Ask most trainers or athletes, and they’ll tell you that they know they’re getting warmed up once those first beads of sweat start rolling.

But what even is sweat, and why do some people seem to take forever to start while others can hardly get from the gym parking lot to the locker room without doing it?

We tapped Lindsay Baker, Ph.D., Senior Principal Scientist at the Gatorade Sports Science Institute (GSSI), to find out. She specializes in sweat as it relates to athletes and how they can best hydrate to optimize their performance. Whether you’re a pro or not, knowing why you sweat and how it helps keep you safe is key if you want to push your limits during workouts.

Here are six interesting things you may have been wondering— or have never even considered— about sweating.