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Erythema ab igne

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Erythema ab igne
Kristen Miller MD, Raegan Hunt MD PhD, Julie Chu MD, Shane Meehan MD, Jennifer Stein MD PhD
Dermatology Online Journal 17 (10): 28

Department of Dermatology, New York University, New York, New York


Erythema ab igne is a reticulated, erythematous or hyperpigmented dermatosis that results from chronic and repeated exposure to low levels of infrared radiation. Multiple heat sources have been reported to cause this condition, which include heated reclining chairs, heating pads, hot water bottles, car heaters, electric space heaters, and, more recently, laptop computers. Treatment consists of withdrawing the inciting heat source. Although erythema ab igne carries a good prognosis, it is not necessarily a self-limited diagnosis as patients are at long-term risk of developing subsequent cutaneous malignant conditions, which include squamous cell and merkel-cell carcinomas.


A 55-year-old woman presented to the Charles C. Harris Skin and Cancer Pavilion in February, 2011, for evaluation of a three-week history of boils on her upper legs. During that time she also noticed a hyperpigmented eruption on the medial aspects of both legs although she was unable to definitively say how long this second eruption had been present. Upon further questioning the patient reported using a radiant electric heater under her desk at home. During this past winter she was in the habit of working on her computer for long hours, with the heater positioned approximately three feet from her legs. She denied use of heating pads to the area or using her laptop on her lap. She denied pain or pruritus. Review of systems was negative.

Past medical history included a possible cardiac murmur, dyslipidemia, and carpal-tunnel syndrome. Medications included aspirin and simvastatin. The patient had retired from the police force approximately seven years ago.

A punch biopsy was obtained from a representative patch on the medial aspect of the right lower leg. The patient was counseled to discontinue use of the heater and that the hyperpigmentation would fade over time. She is currently applying emollients to the area.

Physical examination

Figure 1

There were reticulated, interlacing, hyperpigmented patches with a few, scattered, erythematous macules at junctions on the medial aspects of the lower legs, which extend superiorly to the knees and distal aspects of the inner thighs. The outer aspects of the legs were spared.

Laboratory data

A complete blood count and comprehensive metabolic panel were normal. A rapid plasma regain test was negative.


Figure 2

There is effacement of the epidermal rete-ridge pattern, subtle keratinocytic atypia, and occasional necrotic keratinocytes. There are slightly dilated, thin-walled blood vessels within the superficial dermis.


Erythema ab igne (EAI) means redness from fire, and is a reticulated, hyperpigmented, occasionally erythematous and telangiectatic dermatosis that results from chronic exposure to an infrared heat source. EAI historically was associated with prolonged exposure to a fire or stove and, in the past, was ten times more common in women. It was first reported in the United Kingdom associated with the use of peat stoves although it has been present since ancient times. It was given the name Hitze melanose, which means melanosis induced by heat, by German dermatologist Abraham Buschke in the early 1900s [1].

Erythema ab igne is caused by long-term and repeated exposure to low levels of infrared radiation that is usually in the form of heat within the range of 43°C to 47°C, which is below the threshold needed to induce thermal burns [2]. The pathophysiology is unknown, but this level of infrared radiation induces changes in dermal elastic fibers that are similar to those observed in actinically-damaged skin [1, 3].

Erythema ab igne has a characteristic appearance and is a clinical diagnosis. It initially presents as a transient, reticulated, macular erythema that is blanchable. Over time and with repeated exposures, the lesions become hyperpigmented and fixed, with overlying atrophy and occasional telangiectases or hyperkeratosis in later stages. A bullous variant that is associated with late-stage disease also has been described [4]. The eruption is typically asymptomatic although patients occasionally describe a mild burning sensation. The distribution and contour of lesions is related to the location of the heat source and arrangement of intervening layers of clothing [1, 2].

Early histopathologic changes of EAI consist of epidermal atrophy and vasodilation. Later-stage lesions have dermal melanin and hemosiderin deposition and may have epidermal atrophy or hyperkeratosis. Lesions also may develop squamous atypia that is similar to that observed in actinic keratoses. An interface dermatitis with necrotic keratinocytes and basal vacuolar change also has been reported and may reflect the bullous variant of EAI. Increased dermal elastin also may be observed [3, 5].

The prevalence of EAI has decreased in the industrialized world since the introduction of central heating in homes. It remains, however, a pertinent diagnosis [6, 7]. Contemporary heat sources reported to have caused EAI include heated reclining or massage chairs, heating pads, hot water bottles, car heaters, and electric space heaters. The faces and forearms of bakers, glass blowers, and foundry workers also are at risk [8, 9]. Case reports of laptop computer-associated EAI have been increasing in recent years. These lesions are characteristically located on the left anterior thigh because batteries, ventilation fan exhausts, and optical drivers are located on the left side of laptop computers [1, 2, 5, 10].

Treatment of EAI primarily consists of discontinuing use of the heat source. Early-stage lesions typically fade over months whereas the hyperpigmentation associated with more chronic lesions may persist for years. Cosmesis can be of concern to some patients. A group in China reported the successful treatment of EAI with 1064 nm Q-switched Nd:YAG laser with low fluence, which may warrant further investigation into the use of lasers to treat pigment alterations in concerned patients [6]. Topical 5-fluorouracil cream has been shown to successfully clear epithelial atypia that is associated with EAI, which reflects histopathologic overlap with actinic damage [11].

Patients with EAI are at risk for developing cutaneous malignant conditions after a latency period that may last decades. Squamous-cell carcinoma (SCC) has historically been associated with EAI that was caused by hydrocarbon heat sources. It is known by different names in different cultures depending on the inciting heat source. Kang cancer on the lateral hip in China and Tibet results from sleeping on heated bricks, Indian Kangri cancer results from wearing coal-fired clothing warmers, and Irish turf cancer results from prolonged standing in front of peat fires or stoves [1, 7]. Merkel-cell carcinoma (MCC) also has been reported in association with EAI [12, 13]. In this setting both SCC and MCC are at high risk for metastasis, with reported rates as high as 30 percent [1]. A recent case report of cutaneous marginal zone lymphoma that arose in the setting of EAI suggests that chronic exposure to infrared radiation may induce malignant potential in multiple cell lines [14]. These observations reflect that EAI should not necessarily be considered a self-limited diagnosis.


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14. Wharton J, et al. Cutaneous marginal zone lymphoma arising in the setting of erythema ab igne. J Am Acad Dermatol 2010; 62: 1080 [PubMed]

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