Cold-weather warfare
Trench foot is a medical condition caused by prolonged exposure of the feet to damp, unsanitary, and cold conditions at temperatures as warm as for as few as 13 hours. Exposure to these environmental conditions causes deterioration and destruction of the capillaries and leads to morbidity of the surrounding flesh. Affected feet may become numb, affected by erythema (turning red) or cyanosis (turning blue) as a result of poor blood supply, and may begin emanating a decaying odour if the early stages of necrosis (tissue death) set in. As the condition worsens, feet may also begin to swell. Advanced trench foot often involves blisters and open sores, which lead to fungal infections. If left untreated, trench foot usually results in gangrene, which may require amputation. If trench foot is treated properly, complete recovery is normal, though it is marked by severe short-term pain when feeling returns. Trench foot affected tens of thousands of soldiers engaged in trench warfare in World War I. Keeping feet warm and dry, or at least changing into warm and dry replacement footgear, is the best way to avoid trench foot.
Immersion foot syndromes
In the British Army, policies were developed to help the soldiers keep their feet dry - the surest way of preventing the disease. Soldiers were told to dry their feet, and keep them dry by changing socks several times a day. After the first year of the First World War, British troops were instructed to keep at least three pairs of socks with them and to frequently change them. The use of whale oil was also successful in combating trench foot. A British battalion in front line positions could be expected to use ten gallons of whale-oil every day.