heatstroke, profound disturbance of the heat-regulating mechanism of the body, also known as sunstroke. It is characterized by extremely high body temperatures and sometimes by convulsions and coma. The skin is usually hot and dry because the body-cooling process of sweating has ceased. In some cases, however, the skin may feel relatively cool because blood vessels just below the skin have constricted and the overheated blood is not being carried to the surface; an actively exercising person with heatstroke may be sweating freely. Heatstroke is a rare disorder and is more common among elderly and obese people and those with debilitating diseases. Heatstroke, unlike heat exhaustion, is considered a serious threat to life; treatment must be swift to prevent death or serious brain damage from high body temperature. The body should be cooled as quickly as possible by removing the patient to a cool shady place and applying cold water or ice water to the skin. See first aid.