An SPF15 gives approximately 93% protection from UVB rays and SPF30 gives approximately 97% protection from UVB rays but the sunscreen has been doubled. It also measures how long a person can stay in the sun without burning. Reapplication is key when using a daylight defense product so slather on the SPF every 1-2 hours and use an ounce for the entire body and a teaspoon for the face. Also look for terminology such as "broad spectrum protection" which means a product is offering protection against UVA and UVB rays.
