Heat rash (prickly heat) occurs when the sweat ducts to the skin become blocked or swell, causing discomfort and itching.
Heat cramps occur in muscles after exercise because sweating causes the body to lose water, salt, and minerals (electrolytes).
Heat edema (swelling) in the legs and hands can occur when you sit or stand for a long time in a hot environment.
Heat tetany (hyperventilation and heat stress) is usually caused by short periods of stress in a hot environment.
Heat syncope (fainting) occurs from low blood pressure when heat causes the blood vessels to expand (dilate) and body fluids move into the legs because of gravity.
Heat exhaustion (heat prostration) generally develops when a person is working or exercising in hot weather and does not drink enough liquids to replace those lost liquids.
Heatstroke (sunstroke) occurs when the body fails to regulate its own temperature and body temperature continues to rise, often to 105°F (40.6°C) or higher. Heatstroke is a medical emergency. Even with immediate treatment, it can be life-threatening or cause serious long-term problems.