Many conditions can increase your risk for developing a heat-related illness. Environmental conditions, such as a high outdoor temperature or a high indoor temperature without cooling devices, such as fans or air-conditioning, can make it difficult to stay cool. Heat-related illness is also more apt to occur when the humidity is high or when there is no wind or very light wind.

Intense physical exertion or having to wear heavy and restrictive work clothing in hot weather increases your risk of a heat-related illness. Your risk increases as you lose body fluids from sweating without drinking enough to replace those lost fluids and minerals. Your risk also is increased if you have not been able to acclimate to a hot environment and you have had heat-related illness in the past.