General pathology · Environmental pathology
Thermal injury: burns, hyperthermia and hypothermia !
- Mechanism
Too much heat or cold destroys skin and tissue and, when the whole body is affected, can cause shock, organ failure or arrhythmias.
Updated 2026-11-01
What it is
Local heat coagulates proteins of the skin, and depth decides healing. Large burns cause fluid loss, hypermetabolism, infection and inhalation injury. Whole-body heat (heat stroke) or cold (hypothermia) overwhelms thermoregulation and injures every cell. Burns are a major cause of disability in low- and middle-income countries.
Key facts
- Heat stroke: core temperature rises with brain dysfunction; it leads to rhabdomyolysis, DIC, kidney and liver failure.
- Malignant hyperthermia is genetic (RYR1) and triggered by inhaled anaesthetics and succinylcholine.
- Hypothermia slows the heart, causes Osborn (J) waves and can end in ventricular fibrillation.
- Frostbite: ice crystals form in tissue, endothelium is injured and small vessels thrombose.
- A chronic burn scar can develop squamous cell carcinoma (Marjolin ulcer).
Step by step
- Heat coagulates proteins of the epidermis and dermis: a zone of necrosis surrounded by a zone of poor blood flow.
- Mediators released by the burn make capillaries leaky in the whole body.
- Plasma leaves the vessels: oedema, haemoconcentration and hypovolaemic shock (burn shock).
- Hypermetabolism follows: high catecholamines, muscle breakdown and poor healing.
- The dead, avascular eschar is easily infected, classically by Pseudomonas aeruginosa: sepsis.
- Inhaled hot gases and smoke cause airway oedema and carbon monoxide and cyanide poisoning.
Burn depth
| Depth | Layers involved | Appearance | Healing |
|---|---|---|---|
| Superficial | Epidermis only | Red, dry, painful, no blisters | Heals without scar |
| Superficial partial thickness | Epidermis and upper dermis | Blisters, moist, very painful, blanches | Heals from adnexa, little scar |
| Deep partial thickness | Epidermis and deep dermis | Pale, less painful, blanches poorly | Slow; often needs grafts; hypertrophic scar |
| Full thickness | Whole dermis and beyond | White, leathery or charred, painless | Needs grafts; contractures |
Test yourself
Think of the answer, then tap the question to see it.
Why is a full-thickness burn painless?
The whole dermis, including its nerve endings, has been destroyed.
Which organism classically infects burn wounds and causes sepsis?
Pseudomonas aeruginosa, which thrives on the moist, avascular eschar.
What mutation underlies malignant hyperthermia?
Usually RYR1, the calcium release channel of skeletal muscle; anaesthetics trigger uncontrolled calcium release.
What is a Marjolin ulcer?
A squamous cell carcinoma arising in a chronic burn scar or other long-standing wound.
Related
- Shock: types, stages and the organs it damages
- Abnormal repair: chronic wounds, hypertrophic scar, keloid, contracture
- Healing of skin wounds: first and second intention
- Mechanical and electrical injury: abrasion, contusion, laceration, wounds
- Health effects of climate change
Related conditions
- Burns (thermal, chemical, electrical; inhalation injury)
- Heat stroke and heat exhaustion
- Accidental hypothermia
- Frostbite
- Malignant hyperthermia
- Neuroleptic malignant syndrome
- Rhabdomyolysis
- Disseminated intravascular coagulation
- Hypovolaemic shock
- Carbon monoxide poisoning
- Keloid and hypertrophic scar
- Cutaneous squamous cell carcinoma
Elsewhere in DurgiPedia
- Body temperature regulation
- Heat exhaustion and heat stroke
- Hypothermia and cold injury
- Fever
- Skin blood flow
- Skin: epidermis layers, dermis, hypodermis
- Wound healing: phases and scar
Microorganisms
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Burns (World Health Organization, 2026); Heat emergencies: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Hypothermia: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.