Dermatological effects of acute and long-term UV-C exposure: an in vivo study using a portable mercury lamp.

Following the COVID-19 pandemic, portable UV-C radiation sources for disinfection have become increasingly available and integrated into daily life. UV-C devices emitting at 254 nm (mercury lamps) affect skin and eyes, usually causing erythema, burns or photokeratitis. Despite safety recommendations, misuse or accidental exposure remains a risk. Most data on UV-C effects come from cases of accidental overexposure in fixed installations, while portable devices involve different exposure geometry. Users hold the source close throughout the disinfection process, exposing themselves to both direct and reflected UV-C radiation. An in vivo study using male SKH-hr1 mice was conducted in two stages to assess the effects of skin exposure to UV-C radiation from a commercial disinfection device (Hg lamp, 253.7 nm, 5 Wm^-2) under realistic conditions of use. In the first stage, single irradiation doses of 5 Jm^-2, 15 Jm^-2, 30 Jm^-2, 45 Jm^-2 and 60 Jm^-2 were used to determine the minimum erythemal dose. Doses of 45 Jm^-2 and 60 Jm^-2 caused irritation and signs of skin aging including reduced elasticity, wrinkling and dry skin. Based on these findings, the second stage assessed long-term effects with repeated exposures of 45 Jm^-2, 60 Jm^-2, and 100 Jm^-2, irradiating mice 5 times per week for 25 days. Progressive skin damage escalated from mild irritation to significant thickening and premature aging, culminating in erythematous papules indicative of actinic hyperkeratosis. These findings demonstrate that both acute and long-term exposure to UV-C radiation can cause significant skin damage, emphasizing the need for strict adherence to safety guidelines.