Perspiration

Overview
Perspiration (also called sweating or sometimes transpiration) is the production and evaporation of a fluid, consisting primarily of water as well as a smaller amount of sodium chloride (the main constituent of "table salt"), that is excreted by the sweat glands in the skin of mammals. Sweat also contains the chemicals or odorants 2-methylphenol (o-cresol) and 4-methylphenol (p-cresol).

Classification of Sweating
There are four types of sweats:
 * 1) Diaphoresis: Diaphoresis is a cold sweat. Diaphoresis is excessive sweating commonly associated with shock and other medical emergency conditions. It is distinguished from hyperhidrosis by the "clammy" or "cold state" state of the patient.
 * 2) Primary Hyperhidrosis: Primary hyperhidrosis is a condition characterized by abnormally increased perspiration, in excess of that required for regulation of body temperature. This is not a cold sweat.
 * 3) Secondary Hyperhidrosis: Secondary hyperhidrosis is a condition characterized by abnormally increased perspiration, in excess of that required for regulation of body temperature that is secondary to an underlying pathologic process such as infections, disorders of the thyroid or pituitary gland, diabetes mellitus, tumors, gout, menopause, certain drugs, or mercury poisoning. This is not a cold sweat.
 * 4) Night sweats: Sleep hyperhidrosis, more commonly known as the night sweats, is the occurrence of excessive sweating (hyperhidrosis) during sleep. The sufferer may or may not also suffer from excessive perspiration while awake.

In humans, sweating is primarily a means of thermoregulation, although it has been proposed that components of male sweat can act as pheromonal cues. Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water. Hence, in hot weather, or when the individual's muscles heat up due to exertion, more sweat is produced. Sweating is increased by nervousness and nausea and decreased by cold. Animals with few sweat glands, such as dogs, accomplish similar temperature regulation results by panting, which evaporates water from the moist lining of the oral cavity and pharynx. Primates and horses have armpits that sweat similarly to those of humans.

How sweat glands operate
Sweat glands are innervated by the sympathetic nervous system; however, because the primary neurotransmitter involved with the innervation of sweat receptors is acetylcholine, and many of the glands are under the control of the hippocampus via nerve pathways typically thought of as parasympathetic. The nerve terminal releases acetylcholine, which binds to M3 receptors on the sweat gland and causes the secretion of sweat. Acetylcholine is partially degraded by Cholinesterase enzyme (AchE); thus anything which interferes with AchE activity causes excessive sweating.

There are two kinds of sweat glands, and they differ greatly in both the composition of the sweat and its purpose:


 * Eccrine sweat glands are distributed over the entire body surface, but are particularly abundant on the palms of hands, soles of feet, and on the forehead. These produce sweat that is composed chiefly of water with various salts. These glands are used for body temperature regulation.
 * Apocrine sweat glands produce sweat that contains fatty materials. These glands are mainly present in the armpits and around the genital area and their activity is the main cause of sweat odor, due to the bacteria that break down the organic compounds in the sweat from these glands.