The short version
- Trench foot is a non-freezing cold injury to the nerves and small blood vessels of the feet, caused by cold and wet, not by frost[1].
- At sea it has its own names: immersion foot in lifeboat and life raft survivors, and sea boot foot in sailors standing still in rubber boots for at least four hours[1].
- It can develop after 14 to 22 hours in seawater at 0 to 8 °C (32 to 46 °F)[1].
- Do not rewarm the feet fast: rapid rewarming can worsen pain, swelling and tissue damage[1].
What is trench foot?
Trench foot, immersion foot and non-freezing cold injury are the same condition. Moisture is required, and dry cold does not cause it[1]; in the CDC’s words, it occurs when feet are wet for long periods of time[2]. The feet are most often hit, but shipwrecked sailors have also injured hands, knees and buttocks[1].
| Name | Setting | Typical exposure[1] |
|---|---|---|
| Trench foot | On land, even with feet in water | Cold, wet feet for one to three days in most cases |
| Immersion foot | Shipwreck: feet in water in a lifeboat or life raft | Hours to days; 14 to 22 hours in seawater at 0 to 8 °C is enough |
| Sea boot foot, bridge foot | Sailors in rubber sea boots, moving little | At least four hours |
Civilian cases cluster in jobs with long periods of wet feet, and Zafren’s 2021 review names fish processors and harbour workers[1]. Fatigue, poor food intake and immobility make it more likely[1].
How common is trench foot now?
| Group | Finding |
|---|---|
| US forces, Europe, November 1944 | 11,000 cases of trench foot in one month[1] |
| UK brigade, Falklands, 1982 | 76% incidence of non-freezing cold injury[1] |
| US Marine Corps, 2023 to 2024 | Immersion injury was the most common cold injury: 30 of 68 cases (44.1%)[4] |
| US forces deployed abroad, 2023 to 2024 | 18 of 22 cold injuries (81.8%) were immersion injuries[4] |
We found no published US count of trench foot in commercial crews, so military data is the best modern signal. The risk profile matches a fishing deck in winter: wet boots, long watches, little movement.
The four stages
| Stage[1] | When | What the crew will see |
|---|---|---|
| 1. Cold exposure | While cold and wet | Numb feet that feel like blocks of wood, pale or white skin, trouble walking; usually painless |
| 2. Pre-hyperaemic | Hours to days after rescue | Feet still cold and numb, mottled pale blue, possible swelling |
| 3. Hyperaemic | Starts suddenly; days to 10 weeks | Hot, red, swollen feet with strong pulses and severe pain |
| 4. Post-hyperaemic | Weeks to years, sometimes permanent | Cold-sensitive feet, chronic pain, heavy sweating |
Long-term damage is real. In 26 naval cadets and officers followed for four years, 16 had cold hypersensitivity at two months and 7 developed chronic symptoms[3].
Treatment on board
- Get the person somewhere warm and carry them if they are in the pre-hyperaemic stage, rather than letting them walk[1].
- Treat hypothermia first if present; see cold water immersion survival.
- Rewarm the feet slowly at room temperature: rest, elevation and gentle pat drying. No rubbing, no hot water, no heater[1].
- Elevate above heart level and leave the feet open to air or under loose dressings[1].
- Get radio medical advice on pain. Common painkillers often do little; the UK armed forces use amitriptyline at night[1].
Infection turns a cold injury into an emergency
Antibiotics are needed only if cellulitis appears, and blood-filled blisters call for a surgical opinion[1]. A man found partly submerged for three days developed bloodstream infection with Aeromonas and Pseudomonas within hours of admission[5]. Fever, spreading redness or blackened skin at sea is a medevac decision.
How to prevent trench foot at sea
| Measure | Why |
|---|---|
| Dry socks at least once a day | One of the most effective measures when wet cold cannot be avoided[1] |
| Keep moving on watch | The 7 naval personnel with no symptoms had probably kept their legs moving[3] |
| Synthetic socks, no cotton, no grease | Cotton is very cold when wet; grease or oils probably raise the risk[1] |
| Pair checks of feet and boots | Used with soldiers; rotating people out of the wet is likely the most effective step[1] |
| Feet up whenever possible | Elevation supports circulation in the limbs[1] |
Survivors in a raft cannot change socks, which is why the raft and lifeboat kit matter: see survival craft first aid kit requirements and man overboard survival.
Discovery Health MD writes the cold injury part of a vessel’s medical plan: maritime medical consulting for watch and recovery protocols, and ship medical chest management for the dressings and drugs behind them. See also commercial fishing vessel medical requirements. Book a physician review of your cold weather crew plan.
Common questions
What causes trench foot?
Feet kept cold and wet for long periods, usually in boots that cannot be removed while the person moves little[1].
Is immersion foot the same as trench foot?
Yes. Both are non-freezing cold injury; immersion foot is the name used for shipwreck survivors in lifeboats and life rafts[1].
How long does it take to get trench foot?
Most cases follow one to three days of cold, wet feet, but 14 to 22 hours in cold seawater can be enough[1].
How is trench foot different from frostbite?
Frostbite needs tissue to freeze; trench foot needs moisture and happens above freezing[1].
Should you warm trench foot quickly?
No. Rewarm slowly at room temperature with rest and elevation; rapid rewarming can cause severe pain and more swelling[1].
Can trench foot be permanent?
It can. In one naval group, 7 of 26 developed chronic cold hypersensitivity[3].
How do you prevent trench foot on a boat?
Change into dry socks at least daily, keep moving, avoid cotton and check each other’s feet[1].
