Objective: to report a possibly novel complication of laser hair removal.
Case report: a white-skinned 18-year-old patient discovered an umbilical, brown, and raised lesion while shaving before his second diode laser hair removal session. He sought consultation before his fourth laser session since the lesion further thickened and darkened. Dermoscopy showed no pigmented network, but a few comedo-like openings within an erythematous-light brown scaly and fissured papule, "moth-eaten" borders, and a central crust due to manipulation, suggesting the diagnosis of seborrheic keratosis. We noted that the laser fluence was increased on the umbilical region where hair seemed resistant to treatment. The patient denied a recent history of local sun tanning, sunburns, inflammation, drainage, or manipulation. The lesion cleared, with no short-term relapse, after one session of cryotherapy.
Conclusion: the development of a seborrheic keratosis-like lesion on a densely haired non-sun-exposed umbilicus of a young patient, following pre-laser shaving and high-fluence hair removal diode laser sessions, could have implicated triggering irritation and/or keratinocyte stimulation by red light-engendered reactive oxygen species (ROS) in the skin with silent epidermal mosaicism.
Keywords: Seborrheic keratosis; diode laser; hair removal; umbilicus.