Heat exhaustion

A person with heat exhaustion loses body fluids and salts from being exposed to high temperatures for long periods of time.

Symptoms of heat exhaustion include fatigue as the body becomes dehydrated, blood volume is reduced and blood pressure drops.

Heat exhaustion is a separate condition to heatstroke.

Heat exhaustion risk factors

The risk of heat-related illness dramatically increases when the environmental temperature climbs to 26C or higher. It's important - especially during heatwaves - to pay attention to the maximum temperatures reported in your local weather forecasts and to remember that it will be hotter in the sun than in the shade.

If you live in an urban area, you may be especially prone to develop heat exhaustion during a prolonged heatwave, particularly if there are stagnant atmospheric conditions and poor air quality. In what is known as the 'heat island effect', asphalt and concrete store heat during the day and only gradually release it at night, resulting in higher night-time temperatures.

Other risk factors associated with heat-related illness include:

• Age. Infants and children up to age four, and adults over 75 years old, are particularly vulnerable because they adjust to heat more slowly than other people.
• Health conditions. These include heart, lung or kidney disease, being obese or underweight, having high blood pressure, diabetes, mental illness, sickle cell trait, alcoholism, sunburn and any conditions that cause fever.
• Medications. These include diuretics, sedatives, tranquillisers, stimulants, some heart and blood pressure medications and medications for psychiatric conditions.

Check with your doctor or healthcare provider to see if your health conditions and medications are likely to affect your ability to cope with extreme heat and humidity.

Preventing heat exhaustion

When the temperature is high, it's best to stay indoors in a cool room. If you must go outdoors, you can prevent heat exhaustion by taking these steps:

• Wear lightweight, light-coloured, loose-fitting clothing and a wide-brimmed hat.
• Use a sunscreen with a sun protection factor (SPF) of 15 or more.
• Drink extra fluids. To prevent dehydration, it's generally recommended to drink at least eight glasses of water, fruit juice or vegetable juice per day - more on hot days and when exercising or working outdoors in hot weather. Because heat-related illness can also result from salt depletion, it may be advisable to substitute an electrolyte-rich sports drink for water during periods of extreme heat and humidity.
• Avoid fluids containing either caffeine or alcohol because both substances can make you lose fluids and worsen heat exhaustion. If you have epilepsy or heart, kidney or liver disease, are on fluid-restricted diets, or have a problem with fluid retention, check with your doctor before increasing liquid intake.

Symptoms of heat exhaustion

The most common signs and symptoms of heat exhaustion include:

• Dark-coloured urine and urinating less often than usual (which indicates dehydration)
• Dizziness
• Fainting
• Fatigue
• Headache
• Muscle cramps
• Nausea
• Pale skin
• Confusion
• Profuse sweating
• Rapid heartbeat