ConditionInjuries & poisoning
Trench Foot (Immersion Foot)
Trench foot, or immersion foot, is an injury caused by feet being cold and wet for long periods, usually more than 10 to 12 hours, at temperatures above freezing. Wet socks and boots draw heat away and reduce blood flow, damaging nerves, blood vessels and skin. Feet become numb, swollen, pale or blotchy, then red, hot and very painful once warmed. It affects hikers, soldiers, festival-goers, fishers and people experiencing homelessness. Dry, warm feet and good foot care prevent it.
Also called: Immersion foot, non-freezing cold injury (NFCI), trench foot syndrome, shelter foot
At a glance
- What it is
- A non-freezing cold injury from prolonged cold, wet feet.
- When it develops
- Typically after 10 to 12 hours or more of wet, cold conditions (0 to 15 °C, 32 to 60 °F), sometimes sooner.
- Symptoms
- Numbness, tingling, swelling, pale or blotchy skin; then red, hot, intensely painful feet after warming.
- First aid
- Get out of the wet, dry the feet gently, warm them slowly, raise them, avoid walking on them.
- Recovery
- Weeks to months; some people have long-term cold sensitivity and nerve pain.
When to get help
Call 911 or go to the ER
- Feet that are black, blistered with dark fluid, or smell bad (possible gangrene or severe infection): call 911 or your local emergency number or go to the ER
- Signs of hypothermia: confusion, slurred speech, drowsiness, uncontrollable shivering or stopped shivering
See a doctor within a day or two
- Numb, swollen, pale or blotchy feet after many hours wet and cold
- Severe pain, blisters or open sores after rewarming
- Redness, warmth and swelling spreading up the leg, or fever (possible infection)
- Trench foot symptoms in someone with diabetes or poor circulation
Book a routine appointment
- Ongoing pain, numbness, sweating or cold sensitivity weeks after a cold injury
Usually safe to manage at home
- Feet that are briefly cold, wrinkled and pale after a wet day but recover fully within an hour of drying and warming, with normal feeling
First aid for trench foot
- Get to a warm, dry place.
- Remove wet boots and socks.
- Dry the feet gently by patting; do not rub, which damages skin.
- Warm the feet slowly: use body heat, warm (not hot) air or blankets. Do not use hot water, heating pads or fire, because numb feet cannot feel burns.
- Raise the feet to reduce swelling.
- Avoid walking on the affected feet if possible.
- Give pain relief such as ibuprofen or acetaminophen (paracetamol), following the label dose; pain often becomes severe as the feet warm.
- Seek medical care for any persistent numbness, swelling, blisters or discoloration.
Do not break blisters. Avoid smoking, which reduces blood flow.
How trench foot happens
Water conducts heat away from the skin far faster than air. When feet stay cold and wet:
- blood vessels constrict to conserve body heat, starving tissues of oxygen
- nerves, muscles and skin are damaged
- when the feet warm up, blood rushes back in, causing inflammation, swelling and severe pain (reperfusion injury)
Unlike frostbite, the tissue does not freeze. The name comes from World War I, when soldiers stood for days in waterlogged trenches.
Risk factors
- wet socks and boots worn for long periods, tight footwear
- standing still or immobility
- outdoor workers, soldiers, hikers, campers, fishers, festival-goers
- homelessness
- poor circulation, diabetes, smoking, dehydration, poor nutrition
- previous cold injury
Symptoms and stages
| Stage | Timing | What happens |
|---|---|---|
| During exposure | Hours | Numb, cold, pale, wrinkled feet; clumsy walking; no pain |
| After rewarming (hyperemic) | Hours to weeks | Red, hot, swollen, intensely painful feet; pins and needles; blisters |
| Recovery | Weeks to months | Pain eases; may have sweating, cold sensitivity and nerve pain |
Severe cases can lead to skin breakdown, ulcers, infection and gangrene.
Trench foot vs frostbite vs chilblains
| Trench foot | Frostbite | Chilblains | |
|---|---|---|---|
| Temperature | Above freezing, wet | Below freezing | Cold, damp, above freezing |
| Exposure time | Hours to days | Minutes to hours | Repeated exposure |
| Tissue frozen? | No | Yes | No |
| Appearance | Pale, swollen; then red, hot | White, waxy, hard; then blisters | Itchy, red-purple patches on toes or fingers |
Diagnosis
Trench foot is diagnosed from the history of cold, wet exposure and the appearance of the feet. Doctors check circulation, sensation, skin damage and signs of infection. Tests may include blood tests if infection is suspected, and imaging if gangrene or deep injury is a concern.
Treatment
- keep the feet clean, dry, warm and raised
- pain control; nerve pain medicines such as amitriptyline or gabapentin may be prescribed for persistent pain
- wound care for blisters and ulcers
- antibiotics for cellulitis or other infection
- tetanus booster if skin is broken
- surgery to remove dead tissue in severe cases; amputation is rare with modern care
- physical therapy to restore walking
Long-term effects
Some people have lasting problems for months or years:
- sensitivity to cold
- chronic pain, numbness or tingling
- excessive sweating
- higher risk of future cold injuries
Prevention
- keep feet dry: change into dry socks at least daily, more often in wet conditions
- carry spare socks in a waterproof bag
- wear waterproof, well-fitting boots that do not restrict circulation
- remove boots and dry and air your feet when resting, especially at night
- wiggle toes and move around to boost circulation
- avoid sleeping in wet socks
- check your feet daily for numbness, color change or swelling
Frequently asked questions
What does trench foot look like?
At first the feet look pale, wrinkled, swollen and blotchy, and feel numb and cold. After warming, they turn red, hot, swollen and very painful. Severe cases can develop blisters, ulcers, dark skin or gangrene.
How long does it take to get trench foot?
Trench foot usually develops after 10 to 12 hours or more of cold, wet feet, though it can happen sooner in very cold water or with poor circulation. It does not need freezing temperatures.
How is trench foot treated?
Remove wet footwear, dry the feet gently, warm them slowly without direct heat, raise them and seek medical care. Treatment includes pain control, wound care, antibiotics for infection and, rarely, surgery for dead tissue.
Is trench foot the same as frostbite?
No. Trench foot is a non-freezing injury from prolonged cold and wet. Frostbite occurs when tissue actually freezes at temperatures below 0 °C (32 °F). Both can damage nerves and tissue and need medical care.
Can trench foot heal completely?
Mild cases often heal fully within weeks. More severe cases can take months, and some people are left with long-term cold sensitivity, nerve pain or numbness. Early treatment improves recovery.
Sources
This guide was written from current patient and clinical guidance, including:
- CDC/NIOSH: Cold Stress - Trench Foot or Immersion Foot
- MedlinePlus: Trench foot
- Wilderness Medical Society: Clinical Practice Guidelines for the Prevention and Treatment of Frostbite and Non-Freezing Cold Injury
- NHS: Trench foot
- Merck Manual Consumer Version: Trench Foot