The primary cause of trench foot is long periods of wet, cold feet. But, unlike frostbite, this occurs without freezing temperatures. The condition usually results from exposure to temperatures of between 32 F to 59 F. But a temperature as warm as 60 F could cause trench foot when exposure occurs over a period of at least 10 to 14 hours.
When the feet are cold and moist, destruction to small blood vessels (called capillaries) can lead to the breakdown of surrounding tissue. Constriction (vasoconstriction) and dilation (vasodilation) of the blood vessels is thought to be the cause of local tissue damage. Excessive sweating of the feet can also be a contributing factor to trench foot.
When the feet get cold, they lose heat 24 times faster than dry feet.