UVA, UVB and UPF
UVA and UVB light are two wavelengths of ultraviolet light (long and short, respectively) responsible for sunburn, skin damage and eventually skin cancer. UV protection factor (UPF) is a measure of how much UV light is blocked. Ratings of 15 UPF or higher afford good protection. UPF ratings of 50 may be better, but in truth, the higher the UPF factor, the smaller the added benefit.