While most other mammals can sprint faster than we can (a perk of having four legs), humans have basically evolved to be endurance runners. The theory is that this made us more efficient hunter-gatherers. So what does this have to do with sweat? Well, if it weren’t for how efficiently we produce and dissipate sweat, our ancestors wouldn’t have been able to run long distances while hunting and we probably wouldn’t be able to do things like run marathons. Sweating gets a bad rap, and, sure, it is sort of gross. But sweating is vitally important for body temperature regulation and your overall health. A person’s internal body temperature generally hangs around 98 degrees Fahrenheit. There’s flexibility here, but if your body gets too hot, whether it’s due to the temperature outside, being physically active or having a fever, bad things can happen, for instance, heat stroke. Fortunately, your body has very sophisticated mechanisms for sensing and regulating body temperature. As soon as your body’s internal temperature starts rising, your hypothalamus (a small region in your brain) tells eccrine sweat glands distributed all over your body that it’s time to start cooling you down by producing sweat. Cooling down, however, isn’t as easy as this sweat just dripping off of you. Some of this sweat has to evaporate off of your skin for this process to actually work. That’s because cooling your body via sweating relies on a principle of physics called “heat of vaporization.” It takes energy to evaporate sweat off of your skin, and that energy is heat. As your excess body heat is used to convert beads of sweat into vapor, you start to cool down. The other trade off here, though, is that you also lose water as you sweat and water is critically important for just about every organ in your body. This means that when you’re sweating, you also need to make sure you’re drinking plenty of water. so you can replace the water you lose with water you can use.