There are a number of factors which have been linked to increased risk of heat illness and heat stroke.
Differences between people
Individuals vary considerably in their susceptibility. For example strenuous physical exercise in a hot environment is well known for inducing heat stroke, however individuals have been seen with heat stroke in cool to moderate conditions ie 13 - 28 °C [ 55 - 82 °F ].
Ailments and acquired conditions
* skin disease
* dehydration [which also reduces sweating]
* alcohol or drug abuse
* sleep loss
* jet lag
* eg colds and flu or other respiratory infections
The body's status
* poor physical fitness
* lack of heat acclimatisation
* advanced age
* a previous heat injury
* fit people of small build [ have a good power to weight ratio and heat up faster].
* Females are more prone to heat illness than males during acclimatisation, probably due to higher levels of fat below the skin acting as insulation.
* Females sweat less [ on average ] than males.
* The female body temperature is raised by about 1 °F during the first few days of a period.
In hot dry conditions sun protection is likely to be the main concern. Low humidity will help achieve evaporation through light clothing.
In the rain forest it is tempting to cover yourself to prevent mosquito and other insect bites.
Even tropical clothing can reduce evaporation rates by up to 40%
for the areas they cover.
always be selected to help air circulation and to assist sweat evaporation,
and care should be taken not to over cover the skin unnecessarily.
It is a balance of risks, and humid conditions favour the maximum sweating area being uncovered.
The legs and trunk account for the major evaporation area used by the body when hot. Further the body learns where it is most effective to sweat.
For example, if you exercise with your trunk exposed in temperate conditions, but wear a tropical shirt for protection in the heat, then you will reduce your sweat evaporation, because your trunk is covered, until your body can adjust to different areas to sweat from.