Edited sentence: Advanced immersion foot often involves blisters and open sores, which lead to fungal infections; this is sometimes called tropical ulcer (jungle rot).Affected feet become numb and then turn red or blue.As the condition worsens, they may swell.If left untreated, immersion foot usually results in gangrene, which can require amputation.Trench foot is a medical condition caused by prolonged exposure of the feet to damp, unsanitary and cold conditions