Symptoms of heat exhaustion and heatstroke 

Heat exhaustion and heatstroke can be very serious if they are not treated quickly.

Heat exhaustion 

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

  • very hot skin that feels ‘flushed’
  • heavy sweating 
  • dizziness 
  • extreme tiredness (fatigue)
  • nausea (feeling sick) 
  • vomiting
  • a rapid heartbeat (tachycardia)
  • confusion
  • urinating less often and much darker urine than usual 

A person with heat exhaustion should be moved quickly to somewhere cool and given fluids, preferably water, to drink. They should start to feel better within half an hour.

However, certain groups of people are more at risk of getting heatstroke, or developing complications from dehydration, and should be taken to hospital. These include:

  • children under two years of age 
  • elderly people
  • people with kidney, heart or circulation problems
  • people with diabetes who use insulin

Read more about treating heat exhaustion.


The symptoms of heatstroke can develop over several days in vulnerable people, such as the elderly and those with long-term health problems. These groups are particularly at risk during spells of hot weather.

Symptoms develop more quickly when associated with physical activity. This type of heatstroke, known as exertional heatstroke, usually affects young, active people.  

Symptoms of heatstroke include:

  • high temperature – a temperature of 40°C (104°F) or above is one of the main signs of heatstroke (although it can be diagnosed at lower temperatures and some people can reach these temperatures during physical activity without developing heat exhaustion or heatstroke)
  • heavy sweating that suddenly stops – if the body can't produce any more sweat, the skin will become dry which is a major warning sign that the body has become over-heated and dehydrated
  • a rapid heartbeat
  • rapid breathing (hyperventilation)
  • muscle cramps 

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

  • confusion
  • lack of co-ordination
  • fits (seizures)
  • headache
  • vertigo (the sensation that you're moving or spinning when standing still)
  • restlessness or anxiety
  • problems understanding or speaking to others
  • seeing or hearing things that aren't real (hallucinations
  • loss of consciousness

Heatstroke is a medical emergency. Dial 999 immediately to request an ambulance if you think that you or someone you know has heatstroke.

While waiting for the ambulance to arrive, move the person somewhere cool and give them fluids to drink (preferably water). You could also cool their skin with water by placing a damp flannel or sheet on them or spraying them gently.

It's better to wait for medical supervision before immersing someone fully in water because it could increase their blood pressure significantly (hypertensive response), which could be dangerous for those with cardiovascular disease or those at risk of stroke, such as the elderly.

Read more about treating heatstroke.

Page last reviewed: 29/08/2013

Next review due: 29/08/2015