Stands for “sun protection factor,” a measurement used to determine how much protection a product offers against UV radiation. Sunscreens and some cosmetic products typically list their SPF rating on the their packaging.

Contrary to popular belief, SPF does not directly show the amount of time that a product will allow a person to stay in the sun without taking skin damage; for example, SPF 30 does not mean that the wearer can stay in the sun for 30 hours. SPF refers specifically to UV radiation, and because skin tone and other factors can affect a person’s chances of skin damage, it is important to understand SPF labeling in order to limit chances of sunburns.