Topical amnion‐derived mesenchymal stem cell conditioned medium attenuates chronic ultraviolet B‐induced skin photodamage in hairless mice

Ultraviolet B (UVB) exposure induces epidermal hyperplasia, wrinkle formation, and stress-associated responses; however, practical topical countermeasures remain limited. This exploratory proof-of-concept study evaluated whether topical amnion-derived mesenchymal stem cell conditioned medium (AMSC-CM) attenuates chronic UVB-induced photodamage in hairless mice. Male Hos:HR-1 hairless mice were exposed to escalating UVB doses three times per week for 10 weeks and received no topical treatment, α-minimum essential medium (αMEM) vehicle gel, or AMSC-CM gel immediately after each irradiation session; a nonirradiated group served as a control. Wrinkle severity was graded on endpoint dorsal photographs by a masked evaluator, and skin sections were analyzed for epidermal and dermal thickness and epidermal p21 immunoreactivity. UVB exposure increased wrinkle scores, epidermal thickness, and epidermal p21 positivity relative to nonirradiated controls. Compared with UVB alone, AMSC-CM significantly reduced wrinkle severity (mean score 2.00 vs. 4.50; Holm-adjusted p = 0.035). By contrast, epidermal thickness and epidermal p21 positivity showed directional but nonsignificant reductions after Holm correction. These findings support wrinkle attenuation as the primary statistically supported outcome of this exploratory proof-of-concept study and suggest that topical AMSC-CM may modulate chronic UVB-induced photodamage under controlled dosimetry, while secondary histological and p21-related observations remain preliminary.