Heatstroke occurs when the body is no longer able to cool itself and starts to overheat.
The human body can maintain a stable body temperature in a wide range of different environments. This is known as thermoregulation.
How the body cools itself
There are four ways that the body can cool itself. These are:
- radiation – heat radiates out of the body in the same way as it radiates out of a fire
- convection – cold air or water that crosses the skin cools the body
- conduction – a cooler object that's in direct contact with the skin draws out or conducts heat from the body
- evaporation – the body produces sweat that cools on the skin, lowering the body’s temperature
Normal skin temperature is 32-34°C (89.6-93.2°F). If the outside temperature is higher than your skin temperature, the only way that your body can cool itself is through sweating. Therefore, anything that reduces the amount of sweat that's produced by your body can cause it to overheat. Examples include:
- dehydration – the normal water content of your body is reduced
- wearing tight-fighting clothing
- very hot and humid weather which doesn't allow the sweat to cool
Types of heatstroke
There are two types of heatstroke. They are:
- classic heatstroke
- exertional heatstroke
Classic heatstroke usually affects the elderly, babies and people with chronic (long-term) health conditions. It develops during unusually hot weather, such as during a heatwave.
Exertional heatstroke usually affects young, active people while they're doing strenuous, physical activity for a prolonged period of time in hot conditions. For example, cases of exertional heatstroke can affect:
- athletes
- military personnel
- fire-fighters
Vulnerable groups
Sweat is controlled by a part of the brain called the hypothalamus. The hypothalamus acts like a thermostat that tells the body to produce more sweat when it detects that it's getting hotter.
However, in some elderly people and people with long-term health problems, such as diabetes, the hypothalamus doesn't work as well as it should, putting these groups at increased risk of getting heat exhaustion and heatstroke.
Older women are thought to have a slightly higher risk of heatstroke than older men. This is because women have fewer sweat glands than men and older women are more likely to live alone without immediate help available.
Babies and young children are also at risk as they sweat less and are more affected by dehydration.
People who are unable to keep cool during a heatwave are also more at risk of getting heatstroke. This group may include:
- people with Alzheimer’s disease – a group of symptoms that are associated with a decline in mental abilities, such as memory and reasoning
- people with a disability
- people who are bed-bound
- those who have had too much alcohol
- babies and young children
Read more about how to keep your baby safe during hot weather.
Drugs and medications
There are a number of drugs and medications that can interfere with the body’s ability to regulate temperature. It puts those who use them at more risk of developing heat exhaustion and heatstroke. These include:
- amphetamines – stimulants such as speed and crystal meth
- cocaine
- antipsychotics – these are used to help treat mental health conditions such as schizophrenia
- benzodiazepines – a type of tranquiliser
- beta-blockers and calcium-channel blockers – these are used to treat high blood pressure (hypertension) and some types of heart disease
- diuretics – used to reduce the amount of fluid in your body
