We've all felt it: At first comes the trickle, and then the flood. It's embarrassed us, and even torpedoed a presidential campaign. But when was the last time you were grateful for … sweat? Many are ...

Sweat rarely smells on its own. Body odour develops when bacteria on the skin break down compounds in sweat and release volatile chemicals that evaporate into the air.

Sweat is usually something people try to hide, wipe away or mask with deodorant, but it is also one of the body’s richest, least exploited data streams. Long before a person feels sick, subtle shifts ...