In addition to our opposable thumbs, humans have another unique characteristic—sweating. With two sets of sweat glands, humans use sweating as a way to cool down when overheated, in addition to signifying nervousness. Interestingly, the two are very different, and the reason might gross you out.

Sweating while working out or just overheated is mostly water and a bit of salt that comes from the eccrine glands located under the skin. However, sweat provoked by anxiety comes from the apocrine glands, which are located in the hairy regions of the human body.

Ivan Ong, the head of research and development at Microban, an anti-microbial company told Quartzy that the two forms of sweat are different in chemical makeup and texture. "It’s a thick, milky liquid,” Ong said of nervous sweat. "It’s not just water—it’s fatty acids, steroids, proteins, and that comes from the glands that are associated with hair follicles.”

While it may seem like nervous sweating has no purpose at all aside from unflattering hindrance, some scientists believe it was a way to keep warm when cave dwellers were stressed about staying alive during winter. Because primitive humans were covered in hair, the oily sweat would bind it together to act as a built-in coat. Charming, isn't it?