UV Radiation and Photoaging

Photoaging is the cumulative dermatological damage caused by chronic exposure to solar ultraviolet (UV) radiation, distinct from intrinsic chronoaging. UVA (320–400 nm) penetrates the dermis, generates reactive oxygen species, and induces matrix metalloproteinases (notably MMP-1, MMP-3, MMP-9) that degrade collagen and elastin, producing wrinkles, laxity, and solar elastosis. UVB (280–320 nm) is absorbed in the epidermis, forming cyclobutane pyrimidine dimers and 6-4 photoproducts in DNA; unrepaired lesions drive non-melanoma skin cancer. A single 2 MED UVB exposure suppresses procollagen synthesis for ~24 h. Beyond UV, the skin-aging exposome also includes infrared-A, visible light, particulate air pollution and tobacco smoke. Daily broad-spectrum photoprotection (SPF 30+, UVA-PF ≥ 10) is the only intervention with consistent evidence for slowing measurable photoaging.