8.2 Burns, Cold, Heat & Radiation Injury and the Principles of Wound Healing
Key Takeaways
- Wound healing runs through overlapping phases of haemostasis, inflammation (about days 1 to 4), proliferation (about days 4 to 21), and remodelling that lasts up to 1 to 2 years.
- A healed scar regains only about 80% of the tensile strength of unwounded skin at best, and about 20% by 3 weeks.
- Superficial partial-thickness burns blister, are painful, blanch, and heal in about 2 to 3 weeks, whereas full-thickness burns are leathery, painless, and need excision and grafting.
- The Parkland formula gives 4 mL of crystalloid multiplied by body weight in kg and by the percentage of total body surface area burned over 24 hours, with half in the first 8 hours from the time of injury.
- Hydrofluoric acid burns need copious irrigation and topical calcium gluconate gel, because fluoride ions bind calcium and can cause deep pain and life-threatening hypocalcaemia.
Last updated: September 2026
8.2 Burns, Cold, Heat & Radiation Injury and the Principles of Wound Healing
Normal Wound Healing
| Phase | Timing | Main Events |
|---|---|---|
| Haemostasis | Minutes | Vasoconstriction, platelet plug, fibrin clot; platelets release PDGF and TGF-beta |
| Inflammation | About days 1–4 | Neutrophils clear bacteria, then macrophages remove debris and drive repair with growth factors |
| Proliferation | About days 4–21 | Granulation tissue (fibroblasts, new vessels), re-epithelialisation from wound edges and hair follicles, deposition of type III collagen, wound contraction by myofibroblasts |
| Remodelling (maturation) | 3 weeks to 1–2 years | Type III collagen replaced by type I collagen, cross-linking, scar paling. Tensile strength is about 20% at 3 weeks and reaches about 80% of normal skin at best |
- Primary intention: edges brought together (sutured wound), with minimal scarring.
- Secondary intention: an open wound fills with granulation tissue and contracts, used for infected wounds or some surgical defects.
- Delayed primary (tertiary) intention: closure after a period of open treatment.
Factors that delay healing: ischaemia (arterial disease), venous hypertension, infection and biofilm, diabetes, smoking, malnutrition (protein, vitamin C, zinc), systemic corticosteroids and chemotherapy, previous radiotherapy, pressure, oedema, and advanced age.
Principles of Chronic Wound Care
The TIME framework guides wound bed preparation: Tissue (debride non-viable tissue), Infection or Inflammation (treat and manage biofilm), Moisture balance, and Edge (non-advancing or undermined edges need review, including biopsy to exclude malignancy or pyoderma gangrenosum). Moist wound healing is faster than letting wounds dry out.
| Dressing | Best Use |
|---|---|
| Film | Superficial wounds; secondary dressing |
| Hydrocolloid | Light-to-moderate exudate; promotes autolytic debridement |
| Hydrogel | Dry, sloughy, or necrotic wounds (adds moisture) |
| Alginate / hydrofibre | Heavily exuding and bleeding wounds |
| Foam | Moderate-to-heavy exudate; cushioning |
| Antimicrobial (silver, iodine, honey, PHMB) | Locally infected wounds, for limited periods |
| Negative-pressure wound therapy | Large or deep wounds, graft fixation |
Hypertrophic scars and keloids are covered in the surgical complications section. In brief, keloids extend beyond the original wound and do not regress, and first-line treatment is intralesional triamcinolone with silicone and pressure.
Burns
Burn Depth
| Depth | Tissue Involved | Appearance | Sensation | Healing |
|---|---|---|---|---|
| Superficial (epidermal) | Epidermis | Red, dry, no blisters (sunburn) | Painful | About 7 days, no scar |
| Superficial partial-thickness | Epidermis and upper dermis | Blisters, moist pink base, blanches with brisk refill | Very painful | About 2–3 weeks, little scarring |
| Deep partial-thickness | Epidermis and deep dermis | Mottled red-white, slow or absent refill | Reduced | Over 3 weeks, with scarring; often needs grafting |
| Full-thickness | Entire dermis | White, brown, or black, leathery, no blanching | Painless | Needs excision and grafting |
| Deeper (fourth-degree) | Fat, muscle, bone | Charred | None | Major reconstruction |
Estimating Burn Area
- Rule of nines (adults): head and neck 9%, each arm 9%, front of trunk 18%, back of trunk 18%, each leg 18%, perineum 1%.
- Lund and Browder chart: more accurate, and needed for children, whose heads are proportionally larger.
- Palm method: the patient's palm with fingers is about 1% of body surface.
- Simple erythema is not counted in the total body surface area (TBSA).
Fluid Resuscitation and Referral
- Parkland formula: 4 mL × body weight (kg) × %TBSA of crystalloid (for example Hartmann solution) over 24 hours, half in the first 8 hours from the time of the burn, and the rest over the next 16 hours. Adjust to urine output (about 0.5 mL/kg/h in adults). Formal resuscitation is usually needed for burns over about 15% TBSA in adults and 10% in children.
- Refer to a burn centre for: large burns (over about 10% TBSA in adults, lower in children and the elderly); any full-thickness burn; burns of the face, hands, feet, genitals, perineum, or major joints; circumferential burns (risk of compartment syndrome, which may need escharotomy); electrical, chemical, or inhalation injury; burns at the extremes of age; and suspected non-accidental injury.
Chemical and Electrical Burns
- Chemical burns: remove contaminated clothing and irrigate with large volumes of water for a long time. Alkalis penetrate deeper than acids.
- Hydrofluoric acid: fluoride ions bind calcium and magnesium, causing severe deep pain and possible life-threatening hypocalcaemia and arrhythmia. After irrigation, apply calcium gluconate gel. Deeper injury may need local or intra-arterial calcium gluconate, and calcium and ECG must be monitored.
- Electrical burns: small entry and exit wounds can hide extensive deep muscle damage. Check the ECG, creatine kinase, and urine for myoglobin. Lightning can leave fern-like Lichtenberg figures.
Cold Injury
| Condition | Features | Management |
|---|---|---|
| Frostnip | Reversible pallor and numbness | Rewarm |
| Frostbite | Tissue freezing; superficial (clear blisters) or deep (haemorrhagic blisters, then black eschar) | Rapid rewarming in a water bath at about 37–39 °C, analgesia, avoid refreezing; iloprost or thrombolysis in specialist centres for deep injury; wait for demarcation before amputation |
| Non-freezing cold injury (trench or immersion foot) | Cold, wet exposure over days; painful, swollen feet | Warm and dry; long-term neuropathic pain |
| Chilblains (perniosis) | Itchy or painful red-violet papules on fingers and toes in cold, damp weather | Keep warm, stop smoking, nifedipine; exclude chilblain lupus and cryoglobulins in persistent cases |
Cold panniculitis and cold urticaria are covered in their own sections.
Heat Injury
- Erythema ab igne: reticulate red-brown pigmentation from repeated exposure to heat below the burn threshold (hot water bottles, heating pads, laptops, heaters). It may hint at underlying chronic pain, and long-standing lesions carry a small risk of squamous cell carcinoma.
- Miliaria (heat rash) is covered in the sweat gland section.
Radiation Injury
- Acute radiation dermatitis is graded from 1 to 4 (common terminology criteria): faint erythema or dry desquamation; moist desquamation mostly in skin folds; confluent moist desquamation outside folds; and skin necrosis or ulceration. Management includes gentle washing, emollients, mild topical steroids for inflamed skin, and non-adherent dressings for moist areas.
- Chronic radiation dermatitis: poikiloderma (atrophy, telangiectasia, pigment change), fibrosis, hair loss, and late ulcers that heal poorly.
- Late malignancy: basal cell carcinoma, squamous cell carcinoma, and angiosarcoma (for example of the breast after breast-conserving radiotherapy).
- Radiation recall: inflammation limited to a previously irradiated field after certain drugs (for example some chemotherapy agents).
- Fluoroscopy injury: delayed erythema, ulceration, or sclerosis on the back after long interventional procedures.
Mechanical Injury
- Friction blisters: intraepidermal splits from repeated shear, for example in runners and soldiers.
- Callus and corns: thickened skin from pressure. A hard corn (heloma durum) sits over bony prominences, and a soft corn (heloma molle) lies between toes. Paring separates a corn (central translucent core) from a plantar wart (pinpoint bleeding from capillaries, interrupted skin lines).
- Black heel (talon noir): black dots of intracorneal blood on the heels in athletes, a mimic of melanoma. It pares away.
- Pressure injury: see the geriatric dermatology section.
Test Your Knowledge
A 70 kg man has burns covering 30% of his body surface (excluding areas of simple redness), sustained at 10:00. Using the Parkland formula, how much crystalloid should he receive by 18:00?
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Test Your Knowledge
A cook scalds her forearm. The area has large blisters over a moist pink base that blanches quickly on pressure, and it is very painful. What depth is this burn, and how is it likely to heal?
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Test Your Knowledge
A laboratory worker splashes hydrofluoric acid on her hand. After thorough irrigation with water, what is the specific next treatment?
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Test Your Knowledge
A 45-year-old woman with chronic back pain has reticulate red-brown pigmentation over her lower back. She uses a hot water bottle there every evening. What is the most likely diagnosis?
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