Most commonly seen as SPF, it is a number that is assigned to a product that identifies its ability to protect the skin from sunburn or to protect the skin from turning pink or red when exposed to sun. SPF numbering is regulated by the FDA, and is a measure of the amount of time a person can stay in the sun without getting burned if a sunscreen is applied. Because sunburn results from UVB radiation, not UVA radiation, SPF is primarily a measure of UVB protection. At this time, there is no numbering system to indicate the level of protection a sunscreen can provide from UVA radiation, which affects the deeper layers of skin. See UVA , sunscreens