Hypothermia in the Outdoors: A Practical & Scientific Guide for Hikers

Yannis Athanasiou
Nov 24
4 min read

Updated: Nov 26

Hypothermia is one of those risks that usually feels “far away”… until the moment the weather turns, the wind rises, the rain soaks through your layers, and your body starts losing heat faster than it can produce it.

For hikers and mountain lovers, understanding how hypothermia works — and how to prevent or manage it — is not optional. It’s essential mountain literacy.

This guide blends practical field tips from real mountain experience with evidence-based insights, including findings from a nationwide survey on hypothermia management across Italian HEMS (Helicopter Emergency Medical Services) and international wilderness guidelines.

What Is Hypothermia?

Hypothermia occurs when your core body temperature drops below 35°C.

It is classified into three stages:

Mild: 35–32°C (shivering, cold skin, impaired decision-making)
Moderate: 32–28°C (reduced shivering, confusion, movement difficulty)
Severe: <28°C (unconsciousness, cardiac risk)

One of the most dangerous aspects is how fast it can progress — especially when wind, wet clothing, fatigue, immobilization, or trauma are involved.

How Your Body Loses Heat in the Mountains

As described in the study, heat loss happens through:

Conduction: sitting/lying on cold ground, wet clothes, metal surfaces
Convection: wind stripping away warm air around your body
Radiation: your body radiating heat into cold air
Evaporation: sweat, rain, wet base layers
Wind + wetness = the perfect storm. Even temperatures above 0°C can cause dangerous hypothermia when these combine.

Preventing Hypothermia: What Hikers Absolutely Must Know

1. Master the Layering System

The study highlights that even professional rescue units often lack adequate insulation layers . For hikers, proper layering is your first line of defence.

The ideal “burrito-style” insulation system includes:

Base layer: moisture-wicking (merino/synthetic)
Mid layer: fleece or synthetic insulation
Outer shell: waterproof + windproof
Vapor barrier or emergency foil if wet/windy
Insulating layer: puffy jacket, sleeping bag, dedicated rescue blanket
Ground insulation: foam pad, backpack, or anything that prevents contact with cold surfaces
Head, neck, hands, feet fully covered

Tip: If someone gets cold during a break, insulate them immediately, not after they’re shivering violently.

2. Remove Wet Clothing — But Only If…

Research shows that removing wet clothes becomes harmful if the person is exposed to wind or cold during the process .

Best practice:

Protect from the environment first (shelter, tarp, bothy bag).
Only then remove wet layers.
Replace with dry layers + insulation.

3. Don’t Rely on Foil Blankets Alone

The study reports that most HEMS teams carry only a single reflective foil blanket — which is not enough on its own .

Foil blankets reflect radiant heat, but hypothermic hikers produce almost none.

They must be used as part of a 3–5 layer system, not as standalone protection.

4. Insulate From Below (The Forgotten Rule)

Up to one-third of total heat loss can come from direct contact with cold ground.

Always use:

a foam pad,
your backpack,
a rope bag,
branches/leaves (in emergencies).

Even a jacket folded under the person is far better than nothing.

Recognizing Early Hypothermia Signs on the Trail

Early

Persistent shivering
Slowing pace, clumsiness
Poor decision-making (“altitude brain” even if not at altitude)
Slurred speech

Moderate

Reduced or stopped shivering
Confusion, irrational behavior
Inability to walk steadily
Cold, stiff muscles

Severe

Unconsciousness
Weak or irregular pulse
Dilated pupils
High risk of cardiac arrest

When in doubt, treat as hypothermia. The cost of being wrong is low; the cost of ignoring it can be fatal.

Immediate Field Treatment: What Actually Works

1. Stop further cooling

This is the #1 priority emphasized across rescue guidelines and the HEMS study.
Shelter from wind/rain (tarp, cave, bothy bag).
Remove wet layers only after sheltering.
Build the multi-layer insulation “burrito.”

2. Apply Active External Heating (Carefully)

The study shows that more than half of HEMS teams lack active warming devices — but they are recommended whenever available .

Good tools for hikers:

Chemical heat pads (place on chest, armpits, neck sides — never directly on skin).
Hot water bottles in insulated fabric.
Warm (not hot) drinks if the person is fully conscious.

Avoid:

Rubbing cold limbs: can trigger dangerous cold blood return.
Direct skin heat: causes burns + vasodilation shock.

3. Move Gently

Large movements can cause a “rescue collapse” — a sudden cardiovascular crash.

Handle the person as if they are fragile glass.

4. Hydration & Calories

A mildly hypothermic person burns calories at a huge rate.

Offer:

warm sweet liquids,
easy carbs (chocolate, honey, biscuits).
Only if the person is awake and can swallow safely.

5. Evacuation

If any of the following appear, you must activate rescue:

No shivering
Inability to walk
Altered mental state
Suspected trauma
Core temp likely <32°C
Severe weather with no possibility of rewarming

Helicopter teams in the study emphasize the importance of early evacuation and ECMO-capable center coordination for severe cases (<28°C) .

Gear Checklist for Hypothermia Prevention on Hikes

For every season:

Merino/synthetic base layer
Mid layer fleece
Waterproof shell
Lightweight puffy jacket
Beanie, gloves, neck buff
Spare dry base layer
Emergency bivvy bag or bothy bag
Chemical heaters
Extra calories
Insulation pad (foldable foam)

For guides / groups:

Full hypothermia wrap kit (3–5 layers)
Tarp or shelter
Hot drink thermos
Gloves for patient handling
Basic monitoring (temps, consciousness, mobility)

When Hypothermia Is Life-Threatening

Once core temperature drops near or below 28–30°C, scientific evidence shows the risk of cardiac arrest skyrockets.

At this stage, the person needs rapid evacuation to a hospital capable of ECMO — a rewarming technique with very high survival rates when applied early.

The study notes that structured referral pathways improve survival dramatically — but many systems still lack them .

For hikers, this simply means: