The difference between Heat Exhaustion and Heatstroke

Staying Cool – what’s the difference between Heat Exhaustion and Heatstroke?

We live in what evolutionary biologists call the ‘Goldilocks zone’, (not to hot, or too cold), in which a planet can support life. The sun is responsible for all life on Earth, but it can also prove very hazardous to our health unless important precautions are taken.

Many of our physical characteristics, including skin and hair colour, hair distribution, even the flatness of our nasal bridges, are all shaped by our evolutionary response to the light and heat of the sun as it affects different points on the globe. Normally most of us get along quite nicely at a core temperature of approximately 37.0 degrees centigrade (98.6F), and slightly less at our peripheries. This is the temperature at which our vital functions, such as brain activity and metabolism work best. We also have a number of compensatory mechanisms available to us when we get too hot. Sweating cools the surface of the skin, and flushing helps to give off heat.

Singapore has a tropical climate often with plenty of cloud cover and high rainfall, so it may not feel as scorchingly hot as Egypt, for example, or India.  In hot dry countries, however, it is easy to stick to the shade whereas in South East Asia high humidity can cause overheating even out of the direct glare of the sun.

Most episodes of overheating, or ‘heat exhaustion’, can be treated with fluids and removal to a cooler area. Common sense measures such as sunhats and carrying bottled water are normally sufficient protection. However it is useful to know the warning signs of heatstroke, and what causes them, as overheating can become serious and even life-threatening if not addressed.

Heat Exhaustion

Essentially we run into problems when our internal thermostat struggles to cope with excessive heat and our core temperature rises to up to 40 degrees centigrade (104F). Young children and the elderly are at particular risk as they are less able to regulate their body temperature.  This is ‘heat exhaustion’. The common symptoms are headaches, excessive sweating, nausea and feeling faint. The key danger of heat exhaustion is dehydration and this is essentially responsible for the symptoms mentioned. Removing yourself to a cool place, resting and drinking plenty of fluids will normally cause recovery in about half an hour, with no long term consequences.


If, however, the core temperature goes above 40 degrees centigrade (104F), then we run into more serious problems. We are now absorbing more heat that we can effectively dissipate, causing a failure of our internal thermostat. This is ‘heatstroke’. At this point, our cellular structure and biochemical reactions break down causing failure of vital organs, including the brain. Symptoms include vomiting, confusion, rapid breathing and pulse rate, and agitation. Rapid breathing and pulse rate are signs that the body is trying to make up for dehydration and low blood pressure by pumping blood (and therefore oxygen) to the vital organs before they fail. At the point of failure the body goes into ‘shock’ and loss of consciousness and coma will eventually result. This is a medical emergency and hospital admission for intravenous fluid resuscitation and possibly other measures is warranted.

It is relatively rare that people suffer any serious consequences if they use common sense and make themselves aware of warning signs.

Dr Michael Rodger MBChB MRCGP qualified as a doctor in 2001. He worked in the UK in Cambridge, Oxford and London before relocating to Singapore. He is based at IMC Camden.

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