Symptoms of heat stroke

Heat stroke is a heat related condition that progresses from milder form heat cramps to heat exhaustion and unless treated it turns into heat stroke. Thus identification of earlier phases of heat stroke is vital to prevent life threatening consequences. (1-4)

Heat exhaustion occurs when the core body temperature is above normal 37°C (98.6°F) but below 40°C (104°F). The body loses salts and water and there is a general feeling of illness, faintness and heavy sweating.

This stage needs to be quickly treated by taking the person to a cool place, offering water to drink and removing excess clothing. Within 30 to 40 minutes the patient starts to feel better and there are no lasting ill effects of the condition.

Symptoms of heat exhaustion

Symptoms of heat exhaustion include –

  • Hot and flushed skin that appears as a fever
  • Heavy and profuse sweating
  • Intense thirst
  • Dizziness and fatigue
  • Nausea and vomiting
  • Confusion
  • Headaches
  • Black outs or syncope and sudden fall of blood pressure called orthostatic hypotension
  • Rapid heart rate
  • Passing urine less frequently and passing dark colored urine

When does heat exhaustion turn into heat stroke?

Heat exhaustion may quickly turn into a heat stroke if left untreated. Even with treatment some vulnerable persons may proceed to heat stroke from heat exhaustion. These individuals must be taken to the emergency department immediately.

The vulnerable groups include:

  • infants and babies under two years
  • elderly persons, especially elderly women
  • those with long standing diseases like kidney and heart disease, diabetes mellitus, anorexia, Parkinson’s disease, Alzheimer’s disease, cystic fibrosis etc.

How long do the symptoms of heat stroke take to appear?

The symptoms of heatstroke can develop over several days or even over several hours.

The onset is rapid if heat stroke is associated with strenuous physical activity. This type of heatstroke is referred to as exertional heatstroke. This affects young persons like athletes, manual labours, construction workers, military personnel and firemen.

Symptoms of heat stroke

The symptoms of heat stroke include:

  • Raised body temperatures of over 40°C (104°F).

Heat stroke may also be diagnosed at lower temperatures and some people can reach these temperatures during strenuous physical activity with no signs of heat exhaustion or heatstroke.

  • Sweating that suddenly stops. Persons with heat exhaustion usually sweat profusely. Those with heat stroke stop sweating altogether. This is a warning symptom of dehydration and overheating.
  • Rapid and weak pulse rate
  • Rapid and shallow breathing
  • Muscle cramps due to electrolyte imbalance
  • Mental confusion, lack of co-ordination, restlessness or anxiety, slurring of speech, seizures, hallucinations (seeing or hearing things that are not present) and finally loss of consciousness and even coma.

Progression of heat stroke

As the condition progresses the cells of the body start to breakdown and lose their functional capability at high temperatures.

There may be damage to brain, liver, kidney and muscles. Damage to the brain leads to encephalopathy; to the liver and kidney may lead to acute liver or kidney failure; and damage to the muscles lead to breakdown of muscles called rhabdomyolysis. These conditions may be life threatening.

Treatment of heat stroke

Heat stroke is a medical emergency and the person needs to be moved to a cool place and his or her excess clothing is loosened. Patient is given cool but not cold water to sip. The body is cooled by fanning or placing a wet cloth over it combined with fanning.

Further Reading

Last Updated: May 27, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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