What is Hypothermia?

Hypothermia is a medical condition that occurs when the body loses heat faster than it can produce, causing the core temperature to fall dangerously below normal (36.9°C / 98.6F).

In moderately cold environments, the body's core temperature does not usually fall more than 1°C to 2°C below normal because of the body's ability to adapt. In extreme cold, and without adequate clothing (insulation), the body is unable to compensate for heat loss causing the body's core temperature to fall. The first sign of hypothermia is the sensation of cold, followed by tingling pain, that occurs in the extremities and exposed areas.

As heat loss continues, the pain may become numbness and eventually loss of feeling. At this point, permanent damage to tissues can occur.

As the body's temperature falls below 35°C / 95F, muscle weakness, confusion, and drowsiness are experienced. A further decrease in temperature can lead to coma (27°C / 82F), cardiac arrest (20°C / 68F), and at 17°C / 63F the brain's function ceases.


Signs & Symptoms

Stage Core Temperature Signs & Symptoms
Mild Hypothermia 37.2 - 36.1ºC
(99 - 97ºF)
Normal, shivering may begin.
36.1 - 35ºC
(97 - 95ºF)
Cold sensation, goose bumps, unable to perform complex tasks with hands, shivering can be mild to severe, hands numb.
Moderate Hypothermia 35 - 33.9ºC
(95 - 93ºF)
Shivering, intense, muscles incoordination becomes apparent, movements slow and laboured, stumbling pace, mild confusion, may appear alert. Use sobriety test, if unable to walk a 9 meter (30 foot) straight line, the person is more likely hypothermic.
33.9 - 32.2ºC
(93 - 90ºF)
Violent shivering persists, difficulty speaking, sluggish thinking, amnesia starts to appear, gross muscle movements sluggish, unable to use hands, stumbles frequently, difficulty speaking, signs of depression, withdrawn.
Severe Hypothermia 32.2 - 30ºC
(90 - 86ºF)
Shivering stops, exposed skin blue of puffy, muscle coordination very poor, inability to walk, confusion, incoherent/irrational behaviour, but may be able to maintain posture and appearance of awareness
30 - 27.8ºC
(86 - 82ºF)
Muscle rigidity, semiconscious, stupor, loss of awareness of others, pulse and respiration rate decrease, possible heart fibrillation.
27.8 - 25.6ºC
(82 - 78ºF)
Unconscious, a heart beat and respiration erratic, a pulse may not be obvious.
25.6 - 23.9ºC
(78 - 75ºF)
Pulmonary edema, cardiac and respiratory failure, death. Death may occur before this temperature is reached.


First Aid for Hypothermia

  • Seek medical help immediately.
  • Remove all wet clothing.
  • Wrap the person in blankets or other dry materials to insulate against heat loss to the air and ground.
  • Apply warming devices to the person's core, not to their extremities. Body-to-body contact provides a safe heat source.
  • DO NOT rewarm the person too quickly (e.g., do not use a heating lamp or soak in a hot bath).
  • Provide warm, non-alcoholic, non-caffeinated beverages if safe to do so. Do not force oral fluids if the person is unconscious or convulsing.
  • Perform CPR if the victim stops breathing.
    • NB: Respiratory rate and pulse may slow in hypothermic states.


Preventing Hypothermia

Hypothermia can be prevented by wearing proper clothing and footwear. Extremities such as hands, feet, ears, and nose are most susceptible to cold temperatures. Moisture reduces the insulating value of clothing, so it is important to choose the right garment for the activity. Cotton fibres retain moisture and sweat, therefore cotton socks should be avoided during physical activity. Wool and synthetic fibres are better at wicking moisture away from the skin. Stay dry and seek shelter when needed. Be active/keep moving (without breaking a sweat) unless you need to preserve energy.

Adapted from:
Cold Environments - Health Effects and First Aid
. CCOHS, Government of Canada.