We will now look at the basic physiology of heat stroke:

Heat production

Heat production is determined by the general metabolic rate. Exercise and food consumption both increase metabolic rate. No mechanism exists that actively reduces body heat production.

Heat uptake

The body can absorb heat from the environment. When the surrounding environmental temperature exceeds that of the skin, heat uptake occurs through radiation and conduction.

Heat loss

Heat loss occurs through conduction, convection, radiation, evaporation and respiration.


For conduction to occur a temperature gradient must exist between the skin and the surrounding air. Conduction normally has very little impact as a means of losing heat.

However, if the layer of surrounding air, which is warmed by the skin, is removed and replaced by cooler air (e.g. a cool breeze), heat loss is markedly increased. This process is known as convection.


Infrared energy radiates from the body to the surrounding environment. It is less effective in hot environments.


Evaporation is most effective when the surrounding air is cool and dry.

At very high humidity the body can only tolerate air temperatures up to 33°C. In very dry environments, air temperatures up to 60°C can be tolerated, provided salt and water are replaced.

Breathing produces heat loss by the warming and humidification of inspired air. In a warm, humid environment breathing has little impact on heat loss. In a hot, dry environment evaporation (by sweating) can account for 98% of heat loss.

The ideal environment to maximise heat loss would be cool and dry with the presence of a breeze [2-3].

During normal climatic conditions, southern Europeans do not seem to suffer more deaths from heat stroke than Northern Europeans. Given that average seasonal climate temperatures are higher in southern Europe this may simply reflect better adaptation to a hotter environment.