Photostability: The Back Story of UV Filters

Here’s the story of organic UV filters. They absorb a packet of energy called a photon from incoming UV radiation and hold it briefly in an excited state before releasing it as heat or a lower-energy photon or both, and returning to the unexcited or ground state. The front story is absorption. Everybody knows that story. It’s the functionality of these chemicals and their reason for being in sunscreen formulations. The back story is dissipation. That’s the less familiar story of how, and if, the chemical returns to its ground state. The back story of UV filters is photostability.