Cold injuries are not limited to snow or sub-zero temperatures. In Australia, hypothermia most often develops in cool, wet, windy conditions when hikers are fatigued, under-fuelled, or poorly sheltered. It commonly occurs well above freezing and often progresses quietly.
Understanding how heat is lost, recognising early warning signs, and intervening early can prevent a manageable situation from becoming a rescue.
How the body loses heat
Your body constantly produces heat through metabolism and movement. Hypothermia develops when heat loss exceeds heat production for too long.
Heat is lost in four main ways.
Radiation occurs naturally as warmth transfers from your body to cooler surroundings. The greater the temperature difference, the faster this loss.
Conduction occurs through direct contact with colder surfaces. Water conducts heat away around 25 times faster than air. Wet clothing, sitting on cold ground, or falling into water accelerates cooling dramatically. Staying dry and insulating yourself from the ground are critical protective behaviours.
Convection strips away the thin layer of warm air trapped near your skin. Wind is the main driver. Even moderate wind in damp conditions can increase heat loss rapidly.
Evaporation removes heat as sweat or moisture evaporates. Sweat that helps cool you during movement can become dangerous once you slow down. Damp clothing increases ongoing evaporative heat loss. Managing sweat is therefore just as important as staying dry from rain. See Managing sweat when hiking.
Why hypothermia develops
Whether someone becomes hypothermic depends on three competing factors: the cold challenge, heat retention, and heat production.
The cold challenge includes wind, rain, low temperature, fatigue, and exhaustion. Heat retention depends on clothing insulation, weather protection, shelter, and body composition. Heat production relies on movement, shivering, fitness, and adequate fuel and hydration.
When heat retention and heat production cannot keep up with the environmental challenge, core temperature falls. As it drops, both physical and mental function decline.
Recognising hypothermia early
Hypothermia often develops gradually. Coordination and judgement decline before the person realises what is happening.
A simple memory aid is the “umbles”: stumbles, mumbles, fumbles, and grumbles. Clumsiness, slurred speech, difficulty with simple tasks, irritability, and apathy are early warning signs. Persistent shivering, unusual fatigue, slowing pace, and withdrawal are also common.
Early recognition is critical. Mild hypothermia is far easier to reverse than severe hypothermia.
When it becomes serious
As hypothermia progresses, shivering may slow or stop, walking becomes difficult, and confusion worsens. Collapse or altered consciousness are medical emergencies.
If someone stops shivering, cannot walk, or does not improve with initial warming measures, activate your emergency communication device early rather than waiting. See PLB or Satellite Communicator? for guidance.
Managing mild to moderate hypothermia
The first priority is stopping further heat loss. Get out of wind and rain immediately. Add dry insulation layers. Insulate the person from the ground using sleeping mats, packs, or spare clothing. Use available shelter such as a tent, tarp, or bivvy.
If the person is conscious and able to swallow, provide warm, sweet fluids and easy-to-digest, high-energy food. Fuel supports heat production. Avoid alcohol, which increases heat loss and impairs judgement.
Encourage gentle movement only if the person is coordinated and stable. Trapping existing heat using sleeping bags or shared body warmth is often more effective than attempting rapid rewarming.
Severe hypothermia requires caution
In severe cases, handle the person gently and avoid unnecessary movement. Rough handling can trigger dangerous heart rhythm disturbances in profoundly cold patients. Focus on protecting the core, preventing further cooling, and arranging urgent evacuation.
Do not aggressively rub cold limbs and do not force exhausted individuals to walk.
Other cold weather injuries
Immersion foot, sometimes called trench foot, can develop in cool, wet conditions well above freezing. Prolonged dampness and reduced circulation cause numbness, pain, and mottled skin. Prevention relies on keeping feet as dry as possible, changing socks regularly, and airing feet when conditions allow.
Chilblains result from repeated exposure to cold, damp conditions and usually affect fingers, toes, and ears. Keeping extremities warm and dry is the best prevention.
Frostnip and frostbite are uncommon on most Australian hikes but can occur in alpine regions. Frostnip is mild and reversible. Frostbite involves tissue freezing and requires urgent medical care. Never rub frozen tissue, and prevent refreezing at all costs.
Preventing hypothermia on the track
Most cases are preventable with conservative decisions and simple habits. Check weather forecasts including wind and rain, not just temperature. Adjust pace to avoid excessive sweating. Carry a dry spare insulation layer in a waterproof bag. Eat and drink regularly to maintain heat production. Use windproof outer layers before you feel cold, not after.
If conditions deteriorate faster than expected, turning around early is often the safest choice. Sound judgement is one of the most effective hypothermia prevention tools.
