During extremely hot weather, it is easy to become dehydrated or for your body to overheat.

This can lead to life-threatening heat-related illness such as heat stroke and heat exhaustion.

Heat can also make existing illnesses worse (for example may trigger a heart attack in someone with a heart condition), cause serious permanent injuries (such as damage to the brain or other vital organs), and in extreme cases result in death.

Extreme heat and your body

If the body temperature rises above 37.8 degrees Celsius a person may develop a heat-related illness. In very hot weather, the body must work hard and produce a lot of sweat to keep itself cool.

Sometimes sweating isn’t enough and a person’s body temperature rises rapidly. This is more likely to happen when it is humid, or when a person is dehydrated and cannot produce enough sweat.

Some people are at higher risk of heat-related illness. For example, elderly people and people taking certain medications have difficulty producing sweat. Young children are also at risk as they produce more body heat, sweat less and have more rapid rises in body temperature.

Heat-related illnesses

Heat-related illness includes:


Mild to moderate dehydration makes the heart work faster and leads to reduced fluid available for sweating.

Symptoms of dehydration

First aid for dehydration

  • drink plenty of water or oral rehydration drink
  • move somewhere cool
  • seek medical advice if you start to feel unwell

Heat cramps

Heat cramps may also be a symptom of heat exhaustion.

Symptoms of heat cramps include muscle pains and spasms.

First aid for heat cramps

  • stop all activity
  • rest somewhere cool.
  • drink water or oral rehydration solution.
  • seek medical advice if there is no improvement.

Heat exhaustion

Heat exhaustion is the body’s response to an excessive loss of water and salt contained in sweat.

Those most at risk of developing heat exhaustion are elderly people, people with chronic diseases, and people working or exercising in a hot environment.

If heat exhaustion is not treated, it can turn into heat stroke.

Symptoms of heat exhaustion

  • heavy sweating (cool and moist skin)
  • pale skin
  • fast and weak pulse rate
  • breathing fast and shallow
  • muscle weakness or cramps
  • tiredness
  • dizziness
  • headache
  • nausea or vomiting
  • fainting​

First aid for heat exhaustion

  • rest in a cool place
  • cool yourself down by removing excess clothing, hgentaving a cool bath or shower, and placing cool packs under the armpits, groin or neck
  • rehydrate by drinking cool water or oral rehydration drink

Seek urgent medical attention or call an ambulance if necessary if symptoms worsen or if there is no improvement.

Heat stroke

Heat stroke occurs when the body temperature rises above 40.5 degrees Celsius. Heat stroke is a life-threatening emergency. Immediate first aid is very important to lower body temperature as quickly as possible.

Symptoms of heat stroke

  • a sudden rise in body temperature
  • red, hot and dry skin (sweating has stopped)
  • dry swollen tongue
  • rapid pulse
  • rapid shallow breathing
  • intense thirst
  • headache
  • nausea or vomiting
  • dizziness
  • confusion, poor coordination or slurred speech
  • aggressive or bizarre behaviour
  • loss of consciousness
  • seizures or coma

First aid for heat stroke

  • call Triple Zero 000 and ask for an ambulance
  • if they are unconscious:
    • lay them on their side (recovery position) and check they can breathe properly
    • perform CPR if needed
  • if they are conscious:
    • move them to a cool area and keep them still
    • give them small sips of fluid
    • bring their temperature down using any method available (sponge with cool water, put them in a cool shower, spray with cool water from a garden hose, soak clothes with cool water, place cool packs)

Do not give a person with heat stroke aspirin or paracetamol as they do not help and may be harmful.

Current as at: Thursday 7 April 2022
Contact page owner: Environmental Health