Photodamage

Photodamage is damage caused by exposure to light, particularly ultraviolet (UV) radiation from the sun, but it can also involve visible and infrared wavelengths under certain conditions. In biology, photodamage most often refers to damage to cells and tissues resulting from UV exposure, leading to DNA lesions, oxidative stress, and impaired function.

UVB directly damages DNA, forming cyclobutane pyrimidine dimers and 6-4 photoproducts, which if unrepaired can cause mutations. UVA penetrates deeper and generates reactive oxygen species that damage lipids, proteins, and nucleic acids. Cumulative exposure contributes to photoaging: wrinkles, loss of elasticity, and pigmentary changes, and increases the risk of skin cancers such as basal cell carcinoma, squamous cell carcinoma, and melanoma. The eye and lens can suffer UV-induced damage leading to cataracts and retinal degeneration. In plants, excess light can damage photosystem II, leading to photoinhibition, with protective responses like non-photochemical quenching and antioxidant defenses.

Mechanisms of damage include direct DNA lesions, lipid peroxidation, and protein oxidation; cells deploy repair pathways such as nucleotide excision repair and base excision repair, and can use photoreactivation in some organisms. Prevention focuses on photoprotection: broad-spectrum sunscreens, protective clothing, hats, sunglasses, and shade; minimizing peak sun exposure; and, in some cases, dietary antioxidants.

Beyond biology, photodamage also affects materials such as polymers and coatings through photooxidation, leading to fading, embrittlement, or loss of integrity.