But our scorn of sweat is entirely undeserved. Perspiration is vital to life. It cools our bodies and hydrates our skin; it manages our microbiome and emits chemical cues. Sweat is also a fundamental part of what makes people people. Without it, we wouldn’t be able to run long distances in high heat; we wouldn’t be able to power our big brains and bodies; we wouldn’t have colonized so much of the Earth. We may even have sweat to thank (or blame) for our skin’s nakedness, says Yana Kamberov, a sweat researcher at the University of Pennsylvania. Her team’s recent data, not yet published, suggest that as human skin evolved to produce more and more sweat glands, fur-making hair follicles disappeared to make room. Sweat is one of the “key milestones” in human evolution, argues Andrew Best, a biological anthropologist at the Massachusetts College of Liberal Arts—on par with big brains, walking upright, and the expression of culture through language and art.