CHEMICAL or PHYSICAL? The UV radiation in sunlight consists of UV-A, UV-B, and UV-C rays. UV-A and UV-B are both responsible for photoaging, skin cancer, sunburn, tanning, and wrinkling. UV-C is not a factor in skin health, as it is absorbed by the Earth’s atmosphere and does not reach us in significant amounts. Broad-spectrum sunscreen protects against both UV-A and UV-B. This protection can work in one of two ways: chemical or physical.