Which factor contributes to rapid hypothermia onset?

Rapid hypothermia onset is significantly influenced by being wet. When a person is wet, especially in cold environments, their body loses heat much faster than when dry. Water conducts heat away from the body approximately 25 times more efficiently than air at the same temperature. This means that even mildly cold water can hasten heat loss, leading to a drop in body temperature.

Having layers of clothing typically provides insulation and helps to retain body heat. Exposure to sunlight can actually have a warming effect, particularly if the sun is strong and there is no obstruction. While high humidity can enhance feelings of cold and make cool temperatures feel colder, it does not directly contribute to rapid loss of body heat as being wet does. Therefore, being wet is a critical factor in increasing the risk of hypothermia due to the substantial and accelerated heat loss it causes.