SPF stands for sun protection factor. Choose a sunscreen that is waterproof and broadspectrum: it protects against UVA, which causes aging and wrinkles, and UVB which causes sunburns. SPF 15 is suitable for everyday wear. But, if you intend on going to the beach, stick with SPF 30 or higher. Are you wondering what the difference is between the SPF numbers? According to the Skin Cancer Foundation, the number determines how long it would take your skin to burn. So with SPF 30, it would take UVB rays 30 times longer to burn your skin than without sunscreen. Regardless, apply an ounce of sunscreen 30 minutes before going outside, and repeat every two hours. If done properly, you’ll be protected from 97 percent of UV rays.