The primary function of the eccrine sweat glands is to assist in the maintenance of body temperature in response to heat exposure or exercise. Hyperhidrosis may be defined as sweating beyond what is necessary to maintain thermal regulation. It may be primary (idiopathic, essential) or secondary to a number of diseases and prescribed drugs. Hyperhidrosis can be localized or generalized. Regardless of the type or cause of the hyperhidrosis, it is frequently socially embarrassing and occupationally disabling. Excess sweat on the hands may soil paper and art work, and make it virtually impossible to play many musical instruments. Careers in fields that require contact with paper, metal, and electrical components become unrealizable. Axillary and plantar hyperhidrosis may result in stains and damage to clothing and shoes. Generalized hyperhidrosis leaves affected individuals with wet clothing that may have to be changed a number of times each day.

Physiologically, sweating is a function of the sympathetic nervous system. A sweat control center located in the preoptic area and anterior hypothalamus contains neurons that are sensitive to changes in internal temperature and also cerebral cortical events. Sweat glands are innervated by sympathetic postganglionic fibers, but unlike ordinary sympathetic innervation the chemical mediator is acetylcholine. Sweating in response to thermal stimuli is generally acceptable and rarely a cause for complaint. Emotionally induced sweating tends to be localized to the palms, soles, and sometimes the forehead. Axillary sweating may be the result of both emotional and thermal stimuli.

The causes for generalized hyperhidrosis (Display Box 1) include a number of febrile illnesses, neoplastic and neurologic diseases, metabolic disorders, and drugs. The causes and conditions associated with localized hyperhidrosis include primary palmoplantar hyperhidrosis, unilateral circumscribed hyperhidrosis, hyperhidrosis associated with intrathoracic neoplasms, olfactory hyperhidrosis, gustatory hyperhidrosis, spinal cord injuries, and Frey's syndrome. Although primary or essential hyperhidrosis is the most common cause of palmoplantar hyperhidrosis it may also occur in some patients with Raynaud's disease, rheumatoid arthritis, erythromelalgia, nail patella syndrome, keratosis palmaris et plantaris with clindactyly, atrioventricular fistula, and cold injury. Whenever possible, the cause for hyperhidrosis should be identified, and if possible, treated.

Primary or essential hyperhidrosis is a disorder that causes hyperhidrosis of the hands, feet, and sometimes the axillae. It is estimated that 0.6% to 1.0% of the population suffers from this problem. Primary hyperhidrosis may be inherited and in contrast to generalized hyperhidrosis usually has its time of onset in adolescence, but may begin in childhood and even infancy. It characteristically does not occur while sleeping. Primary hyperhidrosis is made worse by heat and emotional stimuli; however, it is important to note that although emotional stimuli are necessary for primary hyperhidrosis to occur in affected individuals, it is not a psychological disease but rather a physiologic disorder. It seems that in patients with primary hyperhidrosis, the hypothalamic sweat centers are more sensitive to emotional stimuli of cerebral origin than in ordinary people. The occasional onset of primary hyperhidrosis in the neonatal period is evidence that this is far more than an emotional disorder! A number of medical and surgical remedies are available for the treatment of hyperhidrosis (Display Box 2).