What is Heat Exhaustion?

Heat exhaustion is a heat-related illness that occurs when the body becomes excessively hot and loses fluids by sweat faster than can be replaced, or when the body cannot transfer heat effectively because external heat gain is excessive. Heat exhaustion is not the same as heatstroke, which is much more serious. Heatstroke can lead to problems with many different organs and can be life-threatening.

A high body temperature (hyperthermia) can develop rapidly in extremely hot environments, or during physical activity in hot temperatures.

Signs & Symptoms

  • 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) - can occur in the legs and / or hands when you sit or stand for a long time in a hot environment.
  • Heat tetany (hyperventilation and heat stress) - 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 40.6°C (105°F) or higher.


First-Aid for Heat Exhaustion

It's best to take measures to prevent heat exhaustion. Drink plenty of non-carbonated, non-caffeinated fluids and limit exposure to heat. Limit or avoid strenuous activity during hot or humid weather, particularly during the hottest part of the day between 11 a.m. and 3 p.m.

If signs of heat exhaustion appear, have the person stop their activity immediately, cool them down, and give them cold, non-caffeinated fluids to drink.


Preventing Heat Exhaustion

  • Drink plenty of fluids, enough so that your urine is light yellow or clear like water.
  • Drink plenty of water before, during, and after you are active. This is very important during physical activity in hot weather.
  • During hot weather, wear light-coloured clothing that fits loosely and a hat with a brim to reflect the sun.
  • Limit or avoid strenuous activity during hot or humid weather, especially during the hottest part of the day (11 a.m. to 3 p.m.). Heat exhaustion and heatstroke usually develop when you are working or exercising in hot weather. Humidity makes hot weather even more dangerous.
  • Try to stay cool during hot weather. Stay indoors - visit public spaces that have air conditioning.

Adapted from:
Heat Exhaustion: Care Instructions
. Government of Alberta.