Heat stroke, also known as sunstroke, is a severe and life-threatening heat illness that occurs when the body overheats and its cooling mechanisms fail. It is characterized by a core body temperature above 40.0 °C (104.0 °F) and can cause red skin, headache, dizziness, confusion, and sometimes seizures or loss of consciousness. Unlike heat exhaustion, in heat stroke the body's temperature regulation malfunctions, leading to dangerously high internal heat that can damage vital organs such as the brain, heart, kidneys, and muscles. Heat stroke typically results from prolonged exposure to high external temperatures or strenuous physical activity in hot conditions. Factors like humidity can exacerbate the condition by reducing the body's ability to cool itself through sweating. There are two primary types: exertional heat stroke (common in athletes or laborers doing intense activity in heat) and classic (non-exertional) heat stroke, which often affects elderly or infirm individuals in hot environments. Symptoms of heat stroke include very high body temperature, confusion, slurred speech, loss of consciousness, hot dry skin (or profuse sweating in exertional cases), nausea, vomiting, flushed skin, rapid breathing, and a racing heart rate. Heat stroke is a medical emergency that requires immediate treatment. Cooling the person rapidly by moving them to shade, removing excess clothing, and applying cool water, fans, or ice packs is critical until professional medical care is available. If untreated, heat stroke can cause permanent organ damage or death. Prevention includes staying hydrated, avoiding prolonged heat exposure, wearing appropriate clothing, and acclimating to hot environments gradually. In summary, heat stroke is a high-temperature medical emergency caused by the failure of the body's temperature regulation, requiring urgent cooling and medical attention.