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[Physiology](https://durgical.com/en/physiology/) · [Temperature, exercise and metabolism](https://durgical.com/en/physiology/#s-integrative)

# Hypothermia and cold injury

- Mechanism
- Exam priority: medium

If the body loses heat faster than it makes it, core temperature falls below 35 °C and everything slows down.

Updated 2026-11-01

Also called: Frostbite, Trench foot

**See it in 3D:** [Skin](https://durgical.com/en/anatomy/skin/)

## Key points

- Mild 32–35 °C (shivering, tachycardia); moderate 28–32 °C (shivering stops, confusion, bradycardia); severe
- Heat lost by conduction (water: ~25 times more than air), convection and radiation exceeds production.
- The hypothalamus constricts skin vessels and triggers shivering; core temperature is defended at first.
- Below ≈32 °C shivering fails and metabolism falls ≈6–7% per °C.
- Cardiac conduction and the CNS slow: bradycardia, confusion and then coma.
- In frostbite, extracellular water freezes and dehydrates cells, and reperfusion causes thrombosis and edema.

## Stages by core temperature

| Parameter | Value | Note |
| --- | --- | --- |
| Mild | 32–35 °C | vigorous shivering, tachycardia, clumsiness |
| Moderate | 28–32 °C | shivering stops, confusion, bradycardia |
| Severe |
- Standard thermometers do not read below ~34 °C: core measurement is needed (esophageal, rectal or bladder).
- Raynaud phenomenon: exaggerated digital vasospasm in the cold (white, blue, red); it is not systemic hypothermia.
- Severe hypothyroidism (myxedema coma) can present with hypothermia.
- In frostbite, rewarming and then refreezing tissue worsens the damage.

## Memory aid

«Below 32, no shiver»: when shivering stops it is not recovery, it is moderate hypothermia.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does a hypothermic patient stop shivering as they get worse?

Below ≈32 °C the hypothalamus and muscle slow down and fuel runs out; shivering stops and temperature falls faster.

## Why do people with hypothermia pass a lot of urine?

Peripheral vasoconstriction shifts blood centrally; volume receptors cut ADH and the cold tubule responds less: cold diuresis.

## Why does immersion in cold water cool far faster than air at the same temperature?

Water conducts heat about 25 times better and holds more heat; convection in moving water removes even more.

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## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Skin](https://durgical.com/en/anatomy/skin/)

## Related topics

- [Body temperature regulation](https://durgical.com/en/physiology/body-temperature-regulation/)
- [Diving, decompression and hyperbaric oxygen](https://durgical.com/en/physiology/diving-decompression-and-hyperbaric-oxygen/)

## Related conditions

- [Raynaud phenomenon](https://durgical.com/en/conditions/raynaud-phenomenon/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [Hypothermia: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000038.htm) (MedlinePlus, US National Library of Medicine, 2026); [Frostbite: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000057.htm) (MedlinePlus, US National Library of Medicine, 2026); [24.6 Energy and Heat Balance](https://openstax.org/books/anatomy-and-physiology-2e/pages/24-6-energy-and-heat-balance) (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 74). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/physiology/hypothermia-and-cold-injury/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/hypothermia-and-cold-injury/