Overview

Erythema ab igne (EAI), often called toasted skin syndrome, is a localized skin change caused by repeated or prolonged exposure to heat or infrared radiation. The condition produces a characteristic netlike (reticulated) pattern of redness that may progress to brownish pigmentation and mild skin thinning. It is not an acute thermal burn but a chronic response of the skin to sub‑burn level heat.

Signs and symptoms

Early lesions are subtle: faint warmth, mild burning or itching and patchy erythema. Over time the affected area develops a lace‑like, hyperpigmented pattern sometimes accompanied by telangiectasia or atrophy. Lesions are usually asymptomatic and may go unnoticed until pigmentation becomes obvious.

Causes and common sources

The trigger is long‑term exposure to a local heat source rather than a single high‑temperature injury. Typical causes include repeated use of hot water bottles, heating pads, localized space heaters, prolonged laptop contact ("laptop thigh"), and traditional stoves or open fires. Heat-driven infrared radiation and conductive heat both may produce the changes.

  • Hot water bottles and heating pads
  • Laptops and other electronic devices
  • Direct exposure to fireplaces, radiators, or industrial heaters
  • Medical heat therapy used chronically for pain relief

Diagnosis, microscopic features and risks

Diagnosis is mainly clinical based on appearance and history of heat exposure. If appearance is atypical or changing, a skin biopsy can be performed; histology often shows epidermal atrophy, pigmentary changes, and superficial vascular alterations. Although usually benign, there are rare reports of premalignant or malignant transformation in long‑standing lesions, so persistent or evolving areas may require further evaluation.

Treatment and prevention

Primary management is eliminating the heat source and avoiding further exposure. Pigmentation sometimes fades slowly after cessation, but persistent discoloration may be treated with topical retinoids, laser therapy, or other dermatologic measures. Preventive advice focuses on reducing chronic heat contact and educating people who use heat for comfort or pain relief.

History and terminology

The disorder has been described under several colloquial names such as hot water bottle rash, granny's tartan, fire stains and toasted skin syndrome. Abbreviation EAI is commonly used in clinical literature. Because the lesion results from cumulative low‑grade thermal injury rather than a true burn, it is often summarized as "heat‑induced pigmentary change" or simply "not a burn" in patient education materials.