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Heat exhaustion and heatstroke - Symptoms of heat exhaustion and heatstroke

NHS Choices Medical Reference

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Heat exhaustion

The symptoms of heat exhaustion can develop rapidly. They include:

  • your skin feeling very hot and flushed,
  • heavy sweating,
  • dizziness,
  • fatigue,
  • nausea,
  • vomiting,
  • tachycardia (a rapid heartbeat), 
  • mental confusion, and
  • urinating less often and the colour of your urine being much darker than usual.


The symptoms of classic heatstroke can develop over several days if you are spending a long time somewhere hot. The symptoms of exertional heatstroke can appear more quickly, usually after physical activity.

Symptoms of heatstroke include:

  • high body temperature: having a temperature of 40°C (104°F) or above is a major sign of heatstroke,
  • heavy sweating that suddenly stops: if the body is unable to produce any more sweat then this is a big warning sign that the body has become over-heated and dehydrated,
  • tachycardia (a rapid heartbeat),
  • hyperventilation (rapid breathing), and
  • muscle cramps.

The extreme heat that causes heatstroke also affects the nervous system, which in turn can cause other symptoms such as:

  • mental confusion,
  • lack of co-ordination,
  • seizures (fits),
  • restlessness or anxiety,
  • problems understanding or speaking to others,
  • hallucinations (seeing or hearing things that are not real),
  • loss of consciousness.

Heatstroke is a medical emergency. If you are worried that you or someone you know may have heatstroke symptoms, dial 999 immediately and ask for an ambulance.


  • High temperature: A high temperature is when your body temperature goes above the normal 37°C (98.6°F). Also known as a fever.
  • Loss of appetite: Loss of appetite is when you do not feel hungry or want to eat.
  • Nausea: Nausea is when you feel like you are going to be sick.
  • Stomach: Your stomach is an organ in your digestive system that helps digest food by mixing it with acids to break it down into smaller pieces.
  • Vomiting: Vomiting is when you bring up the contents of your stomach through your mouth.
  • Hallucinations: A hallucination is when you are seeing, hearing or feeling something or someone that isn't really there.
Medical Review: June 10, 2009
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