Erythema Ab Igne

Updated: Dec 16, 2019
Author: Laila I Al-Otaibi, MBBCh, MSc; Chief Editor: Dirk M Elston, MD 



Erythema ab igne (EAI) is characterized as localized areas of reticulated erythema and hyperpigmentation due to chronic and repeated exposure to infrared radiation. Patients with erythema ab igne have a history of repeated exposures to heat at a lower level than that which causes a thermal burn.[1, 2] Other terms used to describe erythema ab igne include toasted skin syndrome and fire stains.[3]

Initially, the skin in erythema ab igne patients is often mildly erythematous; however, after repeated heat exposures, the classic blue, purple, or brown reticulated hyperpigmentation develops.[1]  See the image below.

Red rash resembling lacework or a fishing net on b Red rash resembling lacework or a fishing net on back.


Erythema ab igne (EAI) is a reticulate hypermelanosis with erythema resulting from repeated heat exposure that induces injury to the epidermis and superficial vascular plexus. The exposure, which need not be of long duration, results in cutaneous hyperthermia in the range of 43-47°C. Erythema ab igne results in histopathologic changes similar to those seen in solar-damaged skin. Although the pathogenic mechanisms in erythema ab igne are poorly understood, one study has shown that moderate heat acts synergistically with ultraviolet radiation to denature DNA in squamous cells in vitro.[4]


Open fires reportedly result in erythema ab igne. Typically, erythema ab igne affects the legs of women aged 40-70 years who use indoor fire as a heat source. Erythema ab igne reportedly affects the face and/or palms of cooks who work over an open fire.

Some patients use a heat source (eg, heating pad, hot water bottle, heated recliner, heated blanket) to relieve chronic pain.[5] In these patients, determine the etiology of the pain. In the case of heating pads and/or hot water bottles, erythema ab igne can occur in patients with pain associated with either primary or metastatic malignancy, as well as with pain associated with chronic pancreatitis.[6, 7, 8] Heated recliners (reclining chairs) have been reported to cause erythema ab igne in patients with chronic lower back pain.[9] The application of heated popcorn kernels applied to the skin to reduce arthritic pain caused erythema ab igne in one patient.[10] One case report describes erythema ab igne in a patient with diabetic neuropathy.[11]

Other heat sources may be involved. Erythema ab igne has been described subsequent to sauna belt usage for abdominal obesity.[12] A car heater reportedly caused erythema ab igne in one patient.[13] More recently, using laptop computers while they are propped on the legs has resulted in the development of erythema ab igne. Some laptop computers can generate significant heat that can result in erythema ab igne when placed on the lap for prolonged periods.[14, 15, 16, 17, 18]

The following is a summary of heat sources reported to cause erythema ab igne[3, 19, 20] :

  • Heating pads

  • Hot water bottles

  • Electric stoves/heater

  • Open fires

  • Coal stoves

  • Peat fires

  • Wood stoves

  • Steam radiators

  • Car heaters

  • Heated reclining chairs

  • Heating or electric blanket

  • Hot bricks

  • Infrared lamps

  • Microwave popcorn

  • Laptop computer

  • Automobile seat heater

  • Hot bathing



United States

Erythema ab igne is rare. Because of the general availability of central heating, erythema ab igne is less common in the United States than in countries where open fires are commonly used for heating.

Historically, erythema ab igne was often seen on the inner thighs and legs of women who sat in front of a stove or open fire.[1, 21] Now erythema ab igne is more commonly related to heating pads or laptop computer use.


Currently, erythema ab igne is most commonly seen internationally following repeated use of hot water bottles, infrared lamps, and heating pads.[22, 23] Additionally, chronic pain in the lumbosacral region and consequent repeated and prolonged use of localized heat to relieve those symptoms has led to an increased incidence of erythema ab igne in this area.[24, 25, 26]

Studies have shown that physiotherapeutic treatments use ultrasound and short-wave diathermy to promote (via high-frequency mechanical waves) an extremely rapid vibration in the tissues in order to generate heat and consequent dilation of the local veins to provide pain relief.[27]


Erythema ab igne has no overt racial predisposition.


Women, in particular those who are overweight, are affected by erythema ab igne more often than men.[1]


Erythema ab igne primarily occurs in adults, usually of middle age (40-70 y).


The prognosis is good, except those cases associated with internal disease or metastatic malignancy. Early changes, such as erythema and little or no hyperpigmentation, may resolve within several months. Chronic and repeated exposure to heat may result in permanent changes such as hyperpigmentation and atrophy. In addition, thermal keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma have been reported within the lesions of erythema ab igne.


Chronic repeated exposure to infrared radiation may result in changes similar to those seen with chronic repeated ultraviolet radiation. Carcinoma can develop from dysplastic keratinocytes harbored within the reticulated hyperpigmentation. Thermal keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma have been reported in patients after chronic exposure to infrared radiation.[28] In one 90-year-old woman with erythema ab igne, Merkel cell carcinoma developed adjacent to squamous cell carcinoma. Occasionally, the first sign of splenomegaly, pancreatitis, pancreatic cancer, and other cancers is erythema ab igne resulting when patients apply external heat to relieve the underlying pain.[21]

Work exposure to heat (eg, for bakers, silversmiths, and boiler operators) may cause erythema ab igne.[1] Additionally, erythema ab igne has been reported to appear on the legs following prolonged, daily exposure to a car heater.

Patient Education

Explain the etiology of the disorder to patients, and emphasize that the cessation of heat exposure is paramount. Inform patients with erythema ab igne about the possibility of malignant degeneration in the affected areas. Educate patients about detection and the need for prompt treatment.




A patient history of excessive exposure to heat in the area of onset facilitates clinical diagnosis of erythema ab igne.[26, 29, 30, 31, 32] The duration of the repeated exposure necessary to provoke alterations in the skin varies from months to several years, and the damage appears to be cumulative.[33] Commonly, patients with erythema ab igne report mild pruritus and burning.

Erythema ab igne is associated with the following:

  • Slight increase in malignancy when the etiology is due to a hydrocarbon heat source

  • Actinic keratosis and squamous cell carcinomas in a number of cases after a long latent period: These include cases from the chronic heat of a sunken hearth (irori) and underfloor braziers covered with a quilt (kotatsu).[34]

  • Heated brick beds in northern China (kang cancers)[34]

  • Coal-burning baskets in Kashmir in India (kangri cancers)[34]

  • Peat fire cancers in Ireland

  • Benzene-burning pots in Japan (kairo cancers)[34]

Physical Examination

The initial presentation is a transient macular erythema in a broad, reticulated pattern that easily blanches. Mild elevation of skin temperature initially results in mild, transient, often reticulated erythema. With prolonged and repeated exposure, areas of reticular erythema persist and, in time, become livid and hyperpigmented. The entire size and shape of the lesion often approximates that of the heat source. See the images below.

Red rash resembling lacework or a fishing net on l Red rash resembling lacework or a fishing net on leg.
Red rash resembling lacework or a fishing net on b Red rash resembling lacework or a fishing net on back.

As the heat exposure continues over time, the erythema evolves into a dusky hyperpigmentation, with lesions fixed and no longer blanchable. Epidermal atrophy may overlie the reticulated pigmentation. Later-stage lesions may become somewhat keratotic, and bullae may appear. Lesions are characteristically asymptomatic, although a slight burning sensation is sometimes noted.

Once the heat source is identified, it is important to determine if it is being used to relieve pain and, if so, the cause of the pain. A lumbosacral location usually suggests musculoskeletal disease or, less often, bony metastases. Erythema ab igne of the abdomen, flank, or mid back may reflect an attempt to relieve pain from inflammation. It may be the only cutaneous manifestation of splenomegaly, pancreatitis, peptic ulcer disease, pancreatic pseudocyst, or pancreatic or gastric cancer.[34, 19] Other unusual sites such as the thigh, pubic area, and upper back can suggest underlying malignancy such as gastric and renal carcinoma, as well as bony metastases.

Symptoms of pain should prompt a thorough review of systems and consideration of a search for occult disease. An inquiry into occupation and hobbies is also important because erythema ab igne can develop in exposed areas (eg, forearms of bakers, face or arms of glass blowers and foundry workers).

The possible development of cutaneous squamous cell carcinoma or Merkel cell carcinoma represents the major long-term risk.[3, 19, 20] The latent period may be 30 years or more. Apparently, the risk of developing squamous cell carcinoma is highest with hydrocarbon-fueled heat exposures, which may include peat fire cancers on the shins of women, Japanese kairo cancers and Tibetan kangri ulcers due to coal-fired clothing warmers, and Chinese kang cancers from sleeping on coal-fire-heated bricks.[34]

It has been recently reported that bullous erythema ab igne can be associated with normochromic normocytic anemia and subclinical hypothyroidism[35] and eating disorders.[36] Additionally, cutaneous reactive angiomatosis and poorly differentiated carcinoma have been reported to arise at the site of erythema ab igne.[37, 38]

Rarely, areas affected by erythema ab igne may become bullous or hyperkeratotic[39] ; in patients with severe long-standing erythema ab igne, poikilodermatous changes may result. Some believe that a bullous variant of erythema ab igne exists, in which bullae and crusts are present on a base of reticulated erythema.[3, 34, 19, 20] Other clinical variants of erythema ab igne are as follows:

  • Bullous lichen planus arising in an area of erythema ab igne

  • Hypertrophic erythema ab igne associated with lymphedema

  • Keloidal erythema ab igne associated with lymphedema


Malignant degeneration may occur and should be monitored.



Differential Diagnoses



Laboratory Studies

Laboratory findings may be abnormal if the erythema ab igne is associated with a systemic disease.


Perform a 3- or 4-mm punch biopsy if the diagnosis of erythema ab igne is uncertain.

Histologic Findings

Microscopic changes in erythema ab igne depend on the type of heat, the length of exposure, and the area of the body involved.[19]


Histologically, erythema ab igne is similar to actinic keratoses, with the epidermis showing squamous atypia.[19] Early erythema ab igne shows atrophy of the malpighian layer and increased epidermal and upper dermal melanin with dermal vasodilatation.[34] Advanced cases show epidermal vacuolation, focal hyperkeratosis, and dyskeratosis.[34] Epidermal dysplasia within abnormal elastic tissue may also be seen.[34] In early erythema ab igne lesions, epidermal atrophy with loss of the rete ridges is seen. Some patients show focal or confluent hyperkeratosis, dyskeratosis, keratinocyte atypia, and, occasionally, melanocyte atypia.[40] Hyperpigmentation, with focal degenerative changes of basal keratinocytes, is seen.[40] Similar alterations can be observed in chronic actinic skin damage.[40]


Melanin incontinence occurs with melanophages present in the upper dermis.[40] Collagen degeneration and a relative increase in dermal elastic tissue are seen. In contrast to solar elastosis, this is not basophilic on hematoxylin and eosin–stained specimens.[40] Telangiectasis within the papillary dermis and occasional hemosiderin may be seen more commonly on the legs in patients with erythema ab igne.[40] An apparent functional activation of melanocytes with numerical increase of dendritic processes is also observed.[40] Abundant melanophages and occasional elastic fiber alterations as seen, similar to actinic elastosis. No alterations consistent with preneoplastic skin conditions are observed.[40]

Increased elastosis with fragmented collagen fibers are seen.[34] Minimal basophilia and homogenization of elastic fibers, which are prominent in solar elastosis, are seen in erythema ab igne.[34] Both melanophages and hemosiderin are seen in the dermis.[34] Varying degrees of dermal lymphohistiocytic infiltration are present.[34] Extravasation of red blood cells in inconsistent.[34] Accumulation of dermal elastic tissue can be seen, which is an early sign of both UV radiation- and heat-induced skin damage.[19]

Other considerations

Squamous cell carcinoma and Merkel cell carcinoma may arise in the lesions of erythema ab igne on rare occasions.[19] The most common thermally induced cancer, squamous cell carcinoma, tends to occur after a long latent period of more than 30 years.[19] Squamous cell carcinoma in burn scars often begins as a chronic ulcer, which slowly enlarges and tends not to heal. Although these carcinomas tend to be of low-to-intermediate grade histologically, they may also be aggressive, with metastases and a poor prognosis reported in greater than 30% of cases.[19] Merkel cell carcinoma is an aggressive neoplasm, characterized by local recurrence in approximately 30% of cases and up to 30% mortality.[19]



Medical Care

No definitive therapy is available for erythema ab igne. Reducing or eliminating exposure to the heat source early in the erythema ab igne disease process may reverse the hyperpigmentation. In cases of short duration, complete resolution occurs with removal of the offending heating device. More advanced cases may respond somewhat to tretinoin, and 5-fluorouracil cream can help clear epithelial atypia.[21, 41]

Surgical Care

In patients with chronic erythema ab igne that results in hyperpigmentation, photothermolysis using the Nd:YAG, ruby, or alexandrite laser may improve the appearance of the lesions of erythema ab igne.


Cessation of chronic heat exposure is paramount in erythema ab igne. In mildly affected patients with little or no pigmentary change, their condition may resolve within several months.


Reducing or eliminating exposure to the heat source can help prevent erythema ab igne development.

Long-Term Monitoring

As in patients with chronic solar damage, monitor patients with erythema ab igne at regular intervals for possible development of thermal keratosis, squamous cell carcinoma in situ, and squamous cell carcinoma. In addition, although not yet reported, other cutaneous malignancies (eg, malignant melanoma) feasibly may develop within the affected areas.