Sweating is controlled by the central nervous system, which sends signals to sweat glands on the skin. Sweating is normal when it happens in response to physical exertion, or if your body senses a threat and goes into “fight or flight” mode. However, the kind of excessive sweating seen in hyperhidrosis is much more than usual, and can be very disruptive to everyday life. The sweat glands are normal in hyperhidrosis, but the signalling from the central nervous system is abnormal. There may be some influence from genetics which is not very well understood.