Perspiration, or sweat, is a watery fluid secreted by the skin as a means of reducing body temperature. Sweating is common in hot climates, after exercise and in the resolution of fever, where the secretion and subsequent evaporation of sweat allow the skin and thus the body to be cooled. Humid atmospheres and high secretion rates delay the evaporation, leaving perspiration on the surface. Excessive fluid loss in sweat, and of salt in the abnormal sweat of cystic fibrosis, may lead to sunstroke. Most sweating is regulated by the hypothalamus and autonomic nervous system. But there is also a separate system of sweat glands, especially on the palms, which secretes at times of stress. Hyperidrosis is a condition of abnormally profuse sweating.