Trench foot (immersion foot) is a cold injury that occurs gradually over several days of exposure to cold, but not freezing, temperatures. The name comes from World War I troops who developed symptoms after standing in cold, wet trenches.

Signs and symptoms of trench foot include:

• Red skin that turns pale and swollen.
• Numbness or burning pain.
• Leg cramps.
• No actual freezing of the skin.
• A slow or absent pulse in the foot.
• Development of blisters or ulcers after 2 to 7 days.

First aid for trench foot includes rewarming the affected areas, relieving pain, and preventing problems such as infection or dead skin (gangrene).