WHAT IS SPF?
The term SPF stands for sun protection factor. Sunscreens combine several ingredients that help prevent the sun’s UV radiation from reaching the skin. UVB is the chief culprit behind sunburn, and UVA rays, which penetrate the skin more deeply, are associated with the various sun-induced effects of ageing.
Sunscreens vary in their ability to protect against UVA and UVB, but most sunscreens with an SPF of 15 or higher do an excellent job of protecting against UVB. How SPF is calculated If it takes 20 minutes for your unprotected skin to start turning red, using a sunscreen with an SPF of 15 theoretically prevents reddening 15 times longer – about five hours.