Introduction

Trench foot, also known as cold immersion foot, is a non-freezing cold injury (meaning ice crystals do not form in the tissues) that damages the soft tissues, nerves, and blood vessels of the foot due to prolonged exposure to damp and cold environments, typically between 0-15°C for 12 hours or more. Nerves, muscles, and endothelial cells (cells that line the interior surface of the blood vessels) are especially vulnerable to damage when reduced blood flow limits the oxygen and nutrients they receive. It can also affect the legs up to the knee, and in 25% of cases, trench foot also affects the hands. Although historically associated with warfare, particularly during World War I, trench foot remains a concern for both military personnel and civilians exposed to similar conditions in temperate climates or during extended outdoor activities.^1,2,3

To understand how trench foot affects circulatory health, we must first understand the skin's role in regulating body temperature.

How the skin controls body temperature in cold conditions

Blood flow to the skin is regulated by skin temperature and is controlled by the hypothalamus, a part of the brain responsible for regulating body temperature.

In cold environments, the foot uses a two-phase response to regulate its temperature and protect the body's core heat. First, it triggers strong vasoconstriction (narrowing of the blood vessels), limiting blood flow and reducing the amount of warm blood reaching the foot. After prolonged exposure to cold, blood flow can drop to as low as 0.2 mL per 100 mL per minute, far below what the tissues need to stay healthy. This drastic reduction in blood flow causes the skin, especially on the toes, to cool rapidly. The foot’s high surface area-to-volume ratio also helps speed up cooling by shunting warm blood away from the extremities. Blood vessel constriction is strongest when the skin temperature reaches around 15°C.

Occasionally, the foot experiences cold-induced vasodilation (CIVD) when the foot temperature drops below 15 °C, where blood flow briefly increases after blood vessel constriction. During CIVD, skin temperature in the toes can rise by up to 10°C in a cyclical pattern, typically lasting 5 to 10 minutes and occurring at regular intervals. This is often called the "hunting response". This response is thought to be caused by arteriovenous anastomoses (AVA) in the skin's blood vessels, allowing blood to bypass the capillaries. While scientists continue to study the exact mechanisms of CIVD, it seems to help protect the foot by increasing blood flow temporarily, which helps maintain tissue health and may improve movement.

Overall, while vasoconstriction is the main response in cold conditions, the occasional CIVD response helps prevent excessive foot cooling and reduces the risk of cold-related tissue damage. While the foot helps maintain the body's core warmth, this protective mechanism also reduces local tissue temperature. If cold exposure continues, it can compromise foot function by significantly reducing blood flow, leading to tissue ischemia and eventual damage.

However,  while the foot helps maintain the body’s core warmth, this protective mechanism also reduces local tissue temperature and compromises foot function if cold exposure continues.^2,4,5

How trench foot impacts blood vessels and tissue perfusion

The circulatory disturbances in trench foot occur in four stages. The duration of each stage can vary greatly between individuals. Some stages may be brief and easily overlooked, while the transition from one stage to another can be quick or prolonged.^1,2,7

Stage 1: Trauma phase

This initial stage occurs immediately when the feet are exposed to cold and wet conditions.

Key characteristics

• Restricted blood flow: Cold exposure causes vasoconstriction to the tissues to preserve heat
• Numbness: Loss of sensation as blood flow is impaired
• Redness of the skin: Blood vessels narrow, causing blood to pool and making the skin appear red
• No pain yet: Since blood flow is still somewhat intact, there is no pain initially, although the tissues are beginning to be affected by reduced circulation

Stage 2: Pre-hyperemic phase (rewarming)

This stage lasts 6 to 24 hours after the person is away from the cold environment. It continues during the rewarming and even after the person has been warmed up.

Key characteristics

• Reduced blood flow makes the skin appear pale or white, and the feet are cold to  the touch
• Paresthesias: The person may feel a tingling sensation (pins and needles) as nerves are affected
• Stiffness: The feet and toes become stiff, making it difficult to move or walk
• The patient may experience delayed capillary refill, diminished or absent pulse in the legs, indicating impaired blood flow

At this stage, the tissues have been subjected to a prolonged lack of adequate blood flow, and hypoperfusion (low blood flow) begins to impair nerve and muscle function.

Stage 3: Hyperemic phase

This stage may persist for up to two months.

Key characteristics

• The affected limbs become painful and feel hot to the touch as blood flow starts to return. However, capillary refill remains delayed
• Oedema (swelling) develops, which worsens with heat, movement, or standing
• In more severe cases, small blisters can appear. These blisters may contain clear fluid
• Tiny red or purple dots (due to haemorrhages) appear on the skin, a sign of small blood vessels breaking

In mild cases, the condition may improve with treatment, and symptoms may resolve within a few weeks. In severe cases, symptoms can progress, leading to potential long-term damage.

Stage 4: Post-hyperemic phase

This stage begins 2 to 6 weeks after initial exposure and can persist long-term. This is an extended vasospastic phase (narrowing of blood vessels).

Key characteristics

• The affected feet may become blue or purple due to poor oxygen to the tissues, which indicates ongoing circulation problems
• The person may develop insensitivity to cold, making the feet feel perpetually cold
• The feet may sweat excessively
• Nail loss 
• Tingling sensations persist as nerves continue to be affected
• Raynaud's syndrome: A secondary condition where the toes become blue or white when exposed to cold and then bright red when warmed up, caused by long-term narrowing of blood vessels

This stage may lead to the need for amputation due to gangrene.

Long-term effects of trench foot

Trench foot primarily affects circulation, and if left untreated, trench foot can cause serious complications over time, including:⁶

• Limb removal due to tissue necrosis
• Extensive fluid-filled lesions 
• Impaired mobility in affected feet
• Tissue necrosis leading to decay
• Irreversible nerve impairment
• Open sores with potential for infection

Interindividual variability and contributing risk factors

Risk factors for trench foot include limited mobility, inability to dry socks and boots, wet or insufficient clothing, fatigue, stress, inadequate nutrition or hydration, excessive mental stress (especially in combat situations), and tight footwear, such as rubberised boots, can restrict circulation and trap sweat and moisture against the skin, further contributing to the injury. 

Additionally, conditions like peripheral vascular disease, diabetes, and Raynaud's phenomenon can increase risk. Older age, Afro-Caribbean ethnicity, smoking (though smoking was not found to be a direct risk factor in a military study), and impaired judgment due to psychosis or alcohol use also increase the risk. Additionally, environmental factors such as immersion in water, wet boots, lack of movement, and general cold exposure contribute to the development of trench foot.^1,2,3

Individuals with better peripheral blood flow or higher skin temperatures are less likely to develop severe trench foot, while those with poor circulation are more vulnerable. Additionally, people with a history of cold-related injuries are at higher risk of re-injury if re-exposed, particularly if they experience residual cold sensitivity.^1,2,3

Diagnosis of trench foot

The diagnosis of trench foot is clinical, based on the patient's history of exposure to cold and wet conditions and a thorough physical examination. Inflammatory markers and imaging studies are used selectively, depending on the presence of complications such as traumatic injury or infection.^1,7

Prevention and treatment of trench foot

Prevention

• Keep feet clean and dry, as dirty and wet foot clothes and socks lose their ability to protect against cold.
• Regularly dry, wash, and change foot cloths and socks. If possible, wear socks with a copper core
• Apply silica gel, antiseptic, and antifungal powders to the feet 
• Dry feet in the air and apply a special cream for lubrication 
• Check the condition of the feet regularly, ideally in the morning and evening 
• Perform mild foot massages to enhance blood circulation
• Sleep with arctic mittens on the feet to retain warmth 
• Avoid smoking and other nicotine-containing products 
• Maintain a high-protein diet to support health 
• Ensure commanders enforce these preventive measures to maintain the unit’s combat effectiveness ^1,3,7

Treatment

Treatment for trench foot primarily focuses on slow rewarming of the affected limbs, often using warm (not hot) water to prevent further tissue damage. Analgesics and anti-inflammatory drugs are prescribed to manage pain and swelling, and, in severe cases, surgical intervention may be necessary to remove dead tissue.^1,3

Other measures taken based on studies include

• Evacuate victims at the first signs of trench foot to prevent further exposure to cold and wet conditions
• Remove wet clothes immediately and provide dry, warm clothing to prevent further cooling 
• Avoid moving the affected limbs, and recommend bed rest 
• Ensure injury avoidance to promote proper recovery 
• Avoid immersing the foot in warm or hot water, as it can worsen the condition. Also, avoid massaging the affected area, as it can cause additional harm 
• Elevate the affected foot to prevent the formation of new blisters 
• Use a fan heater to help keep the foot dry and aid in recovery
• Do not use prophylactic antibiotics. However, administer systemic antibiotics when non-viable tissue is present, or signs of infection appear 
• Treat co-infections with topical antifungals or systemic antibiotics for bacterial infections. Take appropriate measures to prevent tetanus and gas gangrene
• Avoid early surgery unless signs of sepsis, such as elevated C-reactive protein or hyperthermia, are present. If necessary, consider amputation
• Treat macerated or damaged skin with topical antiseptics
• Do not puncture blisters, as this can lead to infection. Provide thorough antiseptic treatment for self-opening blisters and excise necrotic tissue as needed
• Promote early mobilisation to prevent prolonged immobility and reduce the risk of ankylosis (joint stiffness). Provide a high-protein, high-calorie diet to optimise recovery
• Consider including ultrasound frequency oscillation and ultra-high frequency therapies as part of the treatment plan
• In severe cases, if complications such as infection or sepsis occur, consider delayed amputation⁷

Summary

Trench foot develops from prolonged exposure to cold and damp conditions, which damages the foot's tissues due to reduced blood flow and lack of oxygen. Freezing temperatures are not required; the condition can occur even in mild cold if the feet remain damp/wet for an extended period. Trench foot begins with mild symptoms, such as cold and numb feet. If left untreated, it can progress to severe tissue damage, including blisters, gangrene, and potentially irreversible harm to the nerves, muscles, and blood vessels. The severity of the damage depends on the temperature, moisture levels, and duration of exposure. To prevent trench foot, keep the feet dry, warm, and clean. Wear moisture-wicking socks, change wet footwear promptly, and avoid prolonged exposure to cold and damp conditions. If trench foot develops, treatment aims to prevent further damage and promote recovery by warming the affected foot gradually to restore circulation and manage any infections. Surgical intervention may be necessary in severe cases to prevent long-term damage.