Continuing Education Activity

Erythema ab igne is a dermatologic condition characterized by a reticulated pattern of erythema and hyperpigmentation resulting from repeated and prolonged exposure to direct heat or infrared radiation. Common causes include occupational exposure, the use of heating pads, and frequent contact with localized heat sources. While most cases are benign and reversible with removal of the inciting factor, prolonged exposure may lead to permanent pigmentary changes, chronic inflammation, and, in rare cases, malignant transformation. Careful clinical inspection of lesions is required, as erythema ab igne may mimic or mask other dermatologic conditions and, in some cases, demonstrate premalignant features necessitating biopsy. Prognosis is generally favorable when exposure is discontinued; however, delayed recognition or continued exposure increases the risk of complications, including irreversible dyschromia or cutaneous malignancy.

Participants in this activity learn to recognize erythema ab igne early, evaluate patients through detailed history and examination, and determine when biopsy or referral is indicated. Instruction emphasizes differentiating benign heat-related skin changes from lesions with premalignant or malignant potential. Clinicians enhance competence in counseling patients about risk reduction, removal of the offending heat source, and appropriate follow-up care. Interprofessional collaboration among dermatologists, primary care clinicians, pathologists, nurses, and pharmacists is highlighted as critical to improving outcomes by ensuring accurate diagnosis, effective management, and prevention of progression to malignancy. This coordinated team-based approach supports patient safety, minimizes delays in care, and optimizes both functional and cosmetic results.

Objectives:

• Assess the extent of skin involvement, duration of heat exposure, and patient risk factors for malignant transformation.
• Compare the presentation of erythema ab igne with other reticulated dermatoses such as livedo reticularis or cutaneous vasculitis.
• Identify dermoscopic or imaging features that aid in the early detection of premalignant transformation. Implement clinical pathways that standardize recognition, biopsy decisions, and referral processes.
• Enhance collaboration and communication among dermatologists, primary care clinicians, pathologists, nurses, and pharmacists to ensure comprehensive evaluation, treatment, and patient safety in erythema ab igne.

Introduction

Erythema ab igne (EAI) is a cutaneous rash related to chronic long-term heat exposure under the heat required for thermal burns.[1] Erythema ab igne additionally carries a risk of malignant transformation; however, this is more likely in specific situations, such as coal-fire-related heat dermatosis.[1] EAI was previously a common entity in its initial discovery, where it was related to exposure to heat stoves and other direct sources of heat, such as coal fires; however, now this condition is more strongly associated with chronic exposure to electronics, such as laptops or space heaters, particularly in houses without central heating.[2] There are many reports of exposure to various other electronics; however, the main uniting feature is that they all imply chronic exposure to a heat source, including virtual headsets and space heaters, which have increased during the COVID-19 pandemic.[3][4][5] Importantly, chronic exposure to heat sources is below the level required for thermal burns, which is typically reported in situations where the temperature remains below 45 °C.[1] 

Patients often report a history of contact with an external source, which leads to reticular vasodilation, corresponding to the venous plexus pattern of the disease process.[6] Thus, the morphology of EAI is characterized by a localized, reticulated, and erythematous patch with some hyperpigmentation and, rarely, hyperkeratosis.[7] The diagnosis should be clinical, but morphology and distribution provide significant clues. For instance, EAI often appears on the lower back, where people may use a heating pad to alleviate discomfort. Thus, this may indicate that the patient has underlying musculoskeletal issues.[8] Another natural anatomic location is the abdomen, where patients may use a heating pack or even place their laptops in cases of internal pain, such as that from pancreatitis or vomiting.[9][10] 

Finally, space heaters often appear on the anterior legs.[11] However, attention should also be paid to other areas, such as the anterior thighs, in laptop use cases.[12] While the rash is most often benign, its presence can indicate chronic inflammation or, less commonly, systemic illness and should prompt further investigation. Furthermore, careful inspection of the rash may yield evidence of possible premalignant transformation and should prompt referral for biopsy if indicated.[13] Treatment is often observation, although some study results suggest more intensive treatment, particularly in cases of malignant transformation.[1]

Etiology

The rash is nearly always associated with an external heating source and is classified as a chronic environmental dermatosis.[2] The presumed etiology has changed with time. Previously, the rash was correlated with open fires, wood-burning stoves, and kerosene lamps; thus, it was associated with a period that preceded the widespread adoption of central heating.[8] However, etiologic sources have expanded to include laptops and other electronic devices.[9][14] Ultimately, the etiology can be remembered as chronic heat exposure at temperatures required to produce burns.[2] 

Although the direct cause of erythema ab igne is external heat exposure, the cause of rashes in specific areas may be more accurately described. For instance, some people experience EAI in areas of direct heat exposure, such as from space heaters or heating pads, particularly on the anterior legs or lower back.[15][16][17] Yet, the presence of EAI in other areas may suggest a deeper underlying cause. For example, the presence of EAI on the face or ears may implore the clinician to ask further about electronics, the presence on the abdomen may motivate the clinician to ask about internal abdominal pain that causes the patient to use heat there, and the presence of EAI over other areas should cause an exploration of external heat application, its avoidance, and for what reason heat is being used.[18][19][20][21][22]

Epidemiology

Historically, erythema ab igne affects women more often than men and has been reported to be in a 10:1 distribution; however, this is likely older data representing older causes of EAI, such as coal fires and other household issues exposures that women may have had more exposure to traditionally. Newer data suggest that women are about twice as likely to have erythema ab igne, and it is more likely to appear on the anterior legs.[23] Although this condition can appear at any age, results from a previous study noted that the average age was 28.6 years (with a standard deviation of 10.4 years).[23] Most lesions are localized and related to exposure to heaters, stoves, laptops, tandoor ovens, or hot water bags.[23] Notably, the age distribution may be indicative of etiology; for instance, use in older adults for chronic back or abdominal pain may indicate underlying systemic or internal issues, including malignancy.[16]

Pathophysiology

Erythema ab igne occurs from repeated exposure to direct heat or infrared radiation, typically developing over weeks to years at temperatures insufficient to cause significant thermal burns.[1] This chronic heat exposure is proposed to cause damage to superficial blood vessels, such as the venous plexus, which thus corresponds to a reticulated pattern on the skin related to thermoregulatory mechanisms in the integumentary blood vessels.[24] The deposition of hemosiderin and melanin may be a reaction pattern associated with blood vessels, where some capillaries have exhibited endothelial cell changes.[25][26] Continued exposure may eventually lead to hyperkeratosis and hyperelastosis of the affected skin.[27][28]

Histopathology

Changes in the skin at the microscopic level typically occur from cumulative and prolonged exposure to infrared radiation. Initial changes may show epidermal atrophy, vasodilation, and deposition of hemosiderin/melanin in the dermal layer. The presence of melanin may be related to the function of melanocytes. Additionally, dermal capillaries may have enlarged endothelial cells. Later changes may also show focal hyperkeratosis or dyskeratosis with squamous atypia, consistent with changes in actinic keratosis or other premalignant lesions.[1] Given this, biopsies are most useful for excluding more serious conditions such as Merkel and squamous cell carcinoma, which may present with similar skin findings or be masked by erythema ab igne.[16][28][29][30] Further, erythema ab igne may mimic or mask other skin cancers, such as basal cell carcinoma; it may even mask cutaneous metastases of internal malignancy, like colonic adenocarcinoma.[13][31][32]

History and Physical

Patients may seek medical care for this dermatosis, but it often presents as an incidental finding during a physical examination. Patients are usually asymptomatic, but some may complain that the affected area burns, itches, or stings.[27][33] Patients typically present with a history of chronic use of a heating source, such as a pad. This may be associated with pain in the area, such as in the abdomen, lower back, or joints.[18][20][34][20]

Historical findings should focus on contact with any heat source in the rash area. On physical examination, the skin initially presents as easily blanching macular erythema, broadly distributed in one area. This ultimately evolves into the classic reticulated (net-like) dusky hyperpigmentation that is non-blanching.[35][36][37] There may be associated epidermal atrophy on the reticulated hyperpigmentation and focal hyperkeratosis.[7][38]

Evaluation

Erythema ab igne is a clinical diagnosis that raises suspicion, given the relevant history and characteristic skin manifestations. A long-standing disease, accompanied by ulcerations, hyperkeratosis, or bullae, should prompt further evaluation by a dermatologist, as this finding can be associated with the malignant transformation of squamous cell carcinoma.[1][13][39][13] As patients often apply heat to areas of chronic pain, further history should also be obtained from the patient to investigate the cause of the patient's chronic pain, as they may need a further referral for this as well.[40][41]

In ambiguous cases, a biopsy should be considered, particularly as this may mimic or mask underlying skin cancer, such as basal cell carcinoma or squamous cell carcinoma; it may even mask cutaneous metastases of internal malignancy, like colonic adenocarcinoma.[13][31][32] Usually, other laboratory and imaging tests are unnecessary, except when related to the causes of chronic pain. For instance, evaluating the patient for pancreatitis or conducting abdominal imaging for EAI may be indicated to assess underlying pathology.[19][42]

Treatment / Management

The primary treatment of this disease entity is removing the offending heat source.[6] The resulting abnormal pigmentation of affected areas may resolve over months to years; however, permanent hyperpigmentation or scarring may persist. Treatments for hyperpigmentation, such as topical tretinoin or hydroquinone, can help treat persistent hyperpigmentation.[43] Scars can be monitored or treated if they become hypertrophic or disfiguring.[44] 

If epidermal atypia is suspected, regular skin examinations are recommended, particularly since EAI may be associated with squamous atypia and a potential malignant transformation to squamous cell carcinoma.[1] Indeed, pathologic evidence shows that erythema ab igne exhibits histopathologic changes that align with those seen in pre-malignant states, such as actinic keratosis.[13] Therefore, topical 5-fluorouracil has also been shown to treat epithelial atypia if present.[45]

Differential Diagnosis

Erythema ab igne should be considered in the differential diagnosis of dyspigmented reticular dermatoses.[46] Other diagnoses for this pattern of rash include:

• Livedo reticularis
• Livedoid vasculitis
• Poikiloderma atrophicans vascular
• Cutaneous T-cell lymphoma
• Dermatomyositis
• Cutis marmorata telangiectatica congenita
• Genodermatoses
• Angiosarcoma [47]
• Vasculitis [48]
• Bullous disease [17]

A key feature that can distinguish erythema ab igne from other reticular rashes is its presentation in the setting of chronic heat exposure, as livedo reticularis and cutis marmorata are often present with exposure to cold, and other rashes are present without a history of heat exposure altogether.[28] Patients with pancreatitis may have livedo reticularis on the abdomen, chest, or thighs. This is believed to be because of trypsin-induced damage to the subcutaneous venous network, called the Walz sign.[49]

Prognosis

Erythema ab igne typically has a favorable prognosis, provided the offending heat source is removed and repeated exposures are limited. If prolonged exposure continues, there is a risk of permanent skin dyschromia and the potential for transformation into premalignant or malignant skin lesions.[50] There are multiple case reports of malignant transformation of erythema ab igne into squamous cell carcinoma and multiple case reports demonstrating the mimicking or masking of cutaneous malignancy by erythema ab igne. Therefore, there remains a chance of malignant transformation that should be considered in affected areas.[13][31][32]

Complications

Complications are rare; however, malignant transformation to squamous cell carcinoma has been reported in the literature, with signs of hyperkeratosis or ulceration occurring as secondary, premalignant changes.[1]

Deterrence and Patient Education

Patient education on heat as a cause of this disease is essential for the treatment and to prevent a recurrence. Patients diagnosed with this disease due to occupational exposure need specific guidance on preventing exposure and optimizing outcomes. In patients with chronic pain, alternative therapies for pain relief should be advised to avoid repetitive exposures. 

Enhancing Healthcare Team Outcomes

An interprofessional team approach to erythema ab igne, which includes clinicians, specialists (particularly dermatologists), and nursing staff, is recommended. Erythema ab igne is a preventable skin dermatosis, and patient education is critical in preventing disease progression. Most patients present to the primary care clinician. Healthcare professionals can counsel patients on preventive measures and coordinate with pharmacists when medication is necessary. Accurate record-keeping by all interprofessional care team members ensures that everyone involved in the case has access to the same precise patient data; this is another aspect of effective communication between team members. The interprofessional approach yields the best results with the fewest adverse events.

Heating pads and water bottles are commonly used to manage chronic pain and can potentially lead to the development of erythema ab igne. Clinicians should be aware of the presentation of erythema ab igne and other mimicking conditions, such as livedo reticularis, cutis marmorata, and physical abuse. Clinicians should be mindful of the risks for malignant transformation in areas of repeated heat exposure. Furthermore, a careful history should be obtained to rule out other systemic symptoms that could be indicative of other more serious pathologies causing the patient’s chronic pain. Long-standing erythema ab igne, accompanied by other secondary changes such as ulceration or hyperkeratosis, should prompt a referral to a dermatologist for biopsy and further management.

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Disclosure: Nishad Sathe declares no relevant financial relationships with ineligible companies.

Disclosure: Joshua Roach declares no relevant financial relationships with ineligible companies.