Cold weather dominates most conversations about hypothermia, which is the main reason training scenarios, equipment lists, and mental models tend to anchor risk to low ambient temperatures, implicitly linking the condition to extreme environments. While a useful starting point in some situations, this framing is incomplete. 

Hypothermia is not solely an environmental problem, but a physiological consequence of trauma that can develop in conditions most practitioners would consider benign. When injury occurs, the body’s ability to generate and conserve heat quickly becomes compromised. Cold weather accelerates the hypothermia process, certainly, but it is not required for it to begin. In this article, we look at the main hypothermia risk factors and why trauma belongs at the top of the list.

1. Trauma: The Primary Risk Factor

Trauma itself should be recognised as the leading risk factor for hypothermia because it initiates multiple pathways for heat loss and impaired heat production at once. Injury disrupts normal physiology through bleeding, tissue damage, inflammatory response, and stress signalling, which alter how the body generates and retains heat. Unlike environmental exposure (more on this below), which acts from the outside, trauma acts internally and immediately. A casualty does not need to be ‘cold’ to become hypothermic; the process begins at the point of injury. From that moment, every additional factor, from wet clothes and immobility to delayed evacuation, builds on an already unstable thermal state. Positioning trauma at the top of the risk hierarchy reflects how hypothermia actually develops in practice, rather than how it is often taught.

2. Wetness: An Immediate And Overlooked Driver

One of the most consistent and measurable risk factors is wetness. Casualties who are wet have more than double the risk of developing hypothermia. This is not limited to exposure to rain or water immersion. Wet clothes frequently result from blood loss, sweat during exertion, or wound irrigation. Moisture in contact with the skin increases conductive and evaporative heat loss, creating a local environment where heat is steadily drawn away from the body. This process is independent of air temperature. A casualty in damp clothing, lying still, will lose heat in mild or even warm conditions just as predictably as in cold ones, though less visibly.

3. Haemorrhagic Shock: Reduced Heat Production And Retention

Haemorrhagic shock is a third, distinct risk factor. Reduced circulating volume limits peripheral perfusion, impairing the body’s ability to conserve heat. At the same time, decreased oxygen delivery constrains metabolic heat production. The result is a system that both loses heat more readily and is less able to replace it. This is not a secondary effect of the environment but a direct consequence of injury. Even in controlled climates, a shocked patient will tend towards hypothermia if the imbalance is not addressed.

In addition heat loss leads to reduced clotting enzyme and platelet functions, leading to more bleeding. Bleeding and heat loss lead to decreased peripheral perfusion with an increase in anaerobic metabolism which causes acidosis. Both this bleeding and acidosis are associated with greater morbidity and mortality

4. Immobility And Pain: Loss Of Heat Generation

Immobility introduces another independent risk factor. Under normal conditions, continuous low-level muscle activity contributes to baseline heat generation. An injured casualty, whether restricted by fracture, spinal precautions, or pain, loses this mechanism, and pain compounds the problem. While pain may increase physiological stress, it does not generally produce efficient heat generation and can instead contribute to metabolic disruption. The combined effect is a reduction in internal heat production at the same time as external losses continue.

5. Age-related Vulnerability: Limited Thermoregulatory Reserve

Patient characteristics further modify the hypothermia risk. Paediatric and elderly casualties are both more vulnerable to the condition, though for different reasons. Children lose heat more rapidly due to their higher surface area-to-mass ratio and have more limited physiological reserves to compensate. Elderly patients, on the other hand, often have reduced metabolic capacity and diminished vasomotor responses, sometimes compounded by chronic illness or medication. In both groups, the ability to respond to thermal stress is reduced, meaning the same injury produces a greater thermal impact.

6. Time: The Accumulation Of Small Losses

Time acts as a multiplier for all these factors. Hypothermia risk wet clothes, shock, immobility, and reduced physiological reserves do not need to be severe to become significant. During prolonged field care or extended evacuation scenarios, small and initially manageable heat losses steadily accumulate. A casualty who appeared stable early on may deteriorate quickly or unpredictably as these factors interact over time. In mild weather conditions, this progression is easy to miss because there may be no obvious external trigger drawing attention to the risk.

Find Out More

If this perspective reflects gaps you’re seeing in training or operational practice, TSG Associates welcomes the conversation. We work with organisations to examine real-world clinical risk and decision-making. Please get in touch to explore how your teams approach hypothermia, trauma care, and prolonged field conditions.

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