Erythema ab igne

By Dr. Pascal Bafteh · last updated 09/2026

Definition & Pathogenesis

• Erythema ab igne (EAI) — chronically persistent net-like, livid, reticular hyperpigmentation pattern due to repeated prolonged sub-burning heat exposure (>43 °C, below the burn threshold); synonym Buschke heat melanosis.
• Pathogenesis: repetitive heat damages the superficial vascular network and leads to vascular ectasia + dermal melanophages / melanin pigmentation; hemosiderin NOT typical (DD: stasis purpura). End result = persistent reticular pigmentation (melanophage dermatosis) along the cutaneous vascular pattern; histologically also dermal elastosis.

Clinical Presentation

• Reticular, net-like branched erythematous → brown-hyperpigmented streaks corresponding to the superficial cutaneous vascular network.
• Location correlates with heat source: anterior thighs (laptop), lumbar region (hot water bottle, heating pad), anterior lower legs (fireplace), abdomen.
• Subjective: initially asymptomatic or mild burning; chronically persistent.
• Early phase reversible with avoidance; chronic hyperpigmentation can persist for years.

Complications

• Malignant transformation rare, but relevant: chronic EAI can be a precursor for Squamous cell carcinoma or Merkel cell carcinoma in the pigmented plaque. → Biopsy suspicious nodules/ulcerations.

Differential diagnoses

• Livedo reticularis
• Livedo racemosa
• Erythema perstans faciei
• Ashy dermatosis (= Erythema dyschromicum perstans)
• Erythema dyschromicum perstans
• Lupus erythematosus gesicht
• Urticaria

Sources (selection)

1. Plewig 2018 Braun-Falco S.791

More environmental and photodermatoses

• Miliaria Profunda
• Miliaria Pustulosa
• Miliaria rubra (heat rash)
• Favre-Racouchot disease
• Phototoxic reaction

Note: This page is intended for medical education and does not replace diagnosis or treatment decisions in individual cases. Treatment and follow-up content is available in the app.