Erythema ab igne—A Potential Cutaneous Marker of Chronic Heat Use in Patients with Endometriosis: A Narrative Literature Review and a Case Report

Erythema ab igne (EAI), also known as “hot water bottle rash” or “toasted skin syndrome”, is a benign cutaneous condition caused by chronic exposure to low-level infrared heat. It typically begins as transient erythema and evolves into a reticulated brown pigmentation with telangiectasias. A skin biopsy, ideally taken from the central area of the hyperpigmented lesion, is recommended to exclude differential diagnoses. Although usually benign, EAI has been associated with rare malignant transformations, supported only by low-level evidence. Elimination of the heat source is essential, and topical treatments such as hydroquinone or retinoids may be considered, while agents like 5-fluorouracil or imiquimod are reserved for dysplastic lesions. Women with endometriosis frequently use heating devices to alleviate dysmenorrhea and chronic pelvic pain. However, prolonged or inappropriate heat application can lead to chronic thermal injury, including EAI, and may delay medical consultation. While controlled trials confirm short-term analgesic efficacy of heat therapy, extrapolating these findings to unrestricted home use without standardized safety recommendations can be misleading. EAI illustrates the broader impact of chronic pain in endometriosis, linking cutaneous manifestations with neuroplastic alterations and psychiatric comorbidities. A nuanced approach combining patient education on safe use of heat, close dermatologic monitoring, and multidisciplinary pain management is warranted.