Erythema Ab Igne

Erythema ab igne (EAI) is a cutaneous rash related to chronic long-term heat exposure under the heat required for thermal burns. 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. 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. 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. 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.  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. Thus, the morphology of EAI is characterized by a localized, reticulated, and erythematous patch with some hyperpigmentation and, rarely, hyperkeratosis. 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. 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.  Finally, space heaters often appear on the anterior legs. However, attention should also be paid to other areas, such as the anterior thighs, in laptop use cases. 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. Treatment is often observation, although some study results suggest more intensive treatment, particularly in cases of malignant transformation.