Hyperhidrosis is also known as excessive sweating. It is a medical condition thought to be due to overactivity of the nerves that send signals to the sweat glands in the skin. Sufferers sweat profusely in various areas of the body, often when perfectly relaxed and cool. There are prescription anti-perspirants available to help minimize the effects of hyperhidrosis when ordinary anti-perspirants aren't effective enough.