Heat Induced Illness (Hyperthermia)

The normal body temperature is approximately 37C.

The body has a system, located in the brain stem, which controls and regulates the body’s temperature. When this system is overloaded or not functioning correctly, the body’s temperature can rise.

Hyperthermia is a progressive condition. Rises in the body’s temperature can lead to heat cramp followed by heat exhaustion and then heat stroke if left untreated. Cell injury starts to occur at body temperatures of about 42C.

Heat induced illness may be caused by:

  • Excessive heat absorption from a hot environment.
  • Excessive heat production from metabolic activity.
  • Failure of the body’s cooling mechanisms.
  • An alteration in the body’s set temperature.

Recognition of Heat Induced Illness

Mild elevation in body temperature is normally controlled with sweating, which allows cooling by evaporation. Once the individual becomes too dehydrated to sweat, body temperature can rise rapidly and dramatically.

Factors which may contribute to heat induced illness include:

  • Excessive physical exertion.
  • Hot climatic conditions with high humidity.
  • Inadequate fluid intake.
  • Infection.
  • Unsuitable environments (e.g., unventilated hot buildings, parked motor vehicles).
  • Wearing unsuitably heavy, dark clothing on hot days.
  • Drugs which affect heat regulation.

The very young and very old are more prone to heat induced illness.


At no time should children, those living with disability or the elderly be left unattended in parked motor vehicles.

On warm, humid or hot days:

  • Keep infants and the elderly in cool, ventilated areas and provide ample oral fluids.
  • Wear light coloured, loose-fitting clothing during physical exertion and hats during outside activities.
  • Drink adequate fluids during exertion on hot days.

First aid providers may need to prepare for the potential for heat induced illnesses for specific high-risk events, such as events held in high temperatures. Preparation for such events should include the ability to measure temperatures and provide first aid management.


Heat induced illness presents with a spectrum of severity. The person may show the signs of exertion (hot, sweaty, and breathless) but also have some of these indicators/red flags:

  • Inability to continue the activity.
  • High body temperature.
  • Dizziness and faintness.
  • Nausea, vomiting or diarrhoea.
  • Pale skin and other signs of shock.
  • Dry skin.
  • Poor muscle control or weakness.
  • Decreasing levels of consciousness, confusion, or seizures.

The lack of sweating is a sign of serious illness, but only seen in a proportion of the more serious cases.


If the person is not responding and is not breathing normally, commence resuscitation following DRSABCD.

The management of heat induced illness is aimed at cooling and hydration. Cooling the person should be done as soon as practical, but should not delay sending for an ambulance. During cooling management, level of consciousness and the ability to maintain an airway should be continuously assessed.

Cooling management should aim to remove the cause and assist the normal cooling mechanisms of evaporation, conduction, radiation, and convection. Cooling methods will vary depending on availability and circumstance.

Cooling management

  • Lie the person in a cool environment or in the shade.
  • Loosen and remove excessive clothing.
  • Send for an ambulance if not improving quickly.

While waiting for professional assistance for individuals over 5 years of age:

  • Immerse (i.e., whole-body from the neck down) in cold water (a bath if possible, as cold as possible) for 15 minutes. This is the most effective method of cooling. 

If this is not available, a combination of the following methods should be used:

  • Wet the person with cold or cool water, under a shower if safe, or with a hose or other water source.
  • Apply ice packs (groin, armpits, facial cheeks, palms, and soles).
  • Repeatedly moisten the skin with a moist cloth or atomizer spray.
  • Fan continuously.

While waiting for professional assistance for children 5 years of age and under:

  • Cool in a tepid (lukewarm) bath sponging frequently if bath available
  • Repeatedly moisten the skin with a moist cloth or atomizer spray
  • Fan continuously

Hydration management

Oral hydration should only be given if fully conscious and able to swallow. Give cool or cold water to drink if fully conscious and able to swallow.