Sweating is primarily controlled by the central nervous system. Core temperature increments detected by thermosensitive neurons in the hypothalamus stimulate increases in skin blood flow and sweating. The process of sweating is triggered primarily by sympathetic cholinergic stimulation of the eccrine sweat glands, which are distributed ubiquitously over the body surface. Sweat production rates can reach 2 liters per hour for short periods and up to 15 liters per day. Each liter of sweat evaporated from the body surface removes approximately 580 Kcal of heat energy.
Sweat is a hypotonic solution of sodium chloride.
The concentration of sodium chloride in sweat depends on acclimatization state and sweating rate. Higher sweating rates reduce the opportunity for the eccrine secretory epithelium to conserve salt, so, at higher sweat rates, sweat salt concentration rises. Acclimatized sweat glands conserve salt more effectively and produce sweat with reduced salt concentration for any given flow rate. This conservative phenomenon is an important protection from salt depletion in hot environments. Furthermore, reducing the salt content of sweat increases the proportion of intracellular water contributing to sweat formation.