Hyperhidrosis is a condition characterized by abnormally increased sweating, in excess of that required for regulation of body temperature. Although primarily a benign physical burden, hyperhidrosis can deteriorate quality of life from a psychological, emotional, and social perspective. In fact, hyperhidrosis almost always leads to psychological as well as physical and social consequences. It is thus responsible for more than a quarter of the cases of social phobia. Patients suffering from it present difficulties in the professional field, more than 80% of patients experience a moderate to severe emotional impact from the disease and half are subject to depression.

This excess of sweat happens even if the person is not engaging in tasks that require muscular effort, and it does not depend on the exposure to heat. Common places to sweat can include underarms, face, neck, back, groin, feet, and hands. It has been called by some researchers 'the silent handicap'.

Both diaphoresis and hidrosis can mean either perspiration (in which sense they are synonymous with sweating) or excessive perspiration, in which case they refer to a specific, narrowly defined, clinical disorder.