The Risk of Hydroquinone and Sunscreen Over-Absorption via Photodamaged Skin Is Not Greater in Senescent Skin Compared to Young Skin: Nude Mouse as an Animal Model

The study investigated how aging and UV radiation affect the skin's absorption of hydroquinone and sunscreen. Both young and old nude mice were exposed to UVA and UVB radiation, and various methods were used to analyze the effects on their skin. The results showed that UVA radiation degraded epidermal tight junctions and increased COX-2 and TUNEL expression, while UVB radiation led to increased transepidermal water loss, hyperplasia, and inflammation. Hydroquinone penetration was five times higher after UVA or UVA + UVB exposure, but less so with UVB alone, and was lower through senescent skin compared to young skin. Sunscreen components like oxybenzone showed increased flux and skin uptake after both UVA and UVB exposure, but less so than hydroquinone. More lipophilic sunscreens such as avobenzone and ZnO did not show increased absorption in photoaged skin. Overall, the study concluded that photoaging does not increase the skin's absorption of more lipophilic drugs/sunscreens and that percutaneous absorption does not necessarily increase with intrinsic and extrinsic aging.