Overview

The body loses heat through:

• Evaporation of water from your skin if it is wet (sweating). If your clothing is wet, you will also lose some body heat through evaporation and through respiration (breathing) when the body temperature is higher than 37 °C (99 °F). During intense exercise, the body loses 85% of its heat through sweating.
• Radiation (similar to heat leaving a wood stove). This normal process of heat moving away from the body usually occurs in air temperatures lower than 20 °C (68 °F). The body loses 65% of its heat through radiation.
• Conduction (such as heat loss from sleeping on the cold ground). Heat is lost in air temperatures lower than 20 °C (68 °F). The body loses about 2% of its heat through air conduction. However, water causes more heat loss from the body than air does, so heat can be lost from the body very quickly when it is placed in cold water.
• Convection (similar to sitting in front of a fan or having the wind blow on you). The body loses 10% to 15% of its heat through convection.

Heat loss through evaporation and respiration increases in dry, windy weather conditions.

Wet clothing greatly increases heat loss through conduction and evaporation.

Heat loss in cold, wet weather increases the risk for hypothermia and cold injury. Heat loss can occur in warm temperatures through conduction. Swimming or sitting in cool or cold water can cause the body to lose heat very quickly and increase the risk for hypothermia.

Hypothermia can occur quickly (within a few hours) or gradually over days and weeks depending on a person's age, overall health, and environmental conditions.