Sunscreens   can offer protection from two types of ultraviolet (UV) rays  : UVB, which according to the Skin Cancer Foundation, are the chief cause of sunburn and play a key role in the development of skin cancer, and UVA, which get through the skin more deeply and are largely responsible for skin aging and wrinkling, as well as skin cancer risk. The SPF   measurement on sunscreens refers to the UVB protection level -- and the number may not mean what you think it does. SPF 15 doesn't protect you from 15% of UVB rays, just as SPF 100 doesn't protect you from 100% of the rays. In fact, as you get into the higher numbered SPF sunscreens (think: 50 and above), the difference in UVB protection is actually pretty small. Theoretically, though the increase in UVB protection with a super-high SPF sunscreen may be not worth considering, it may help, and certainly can't hurt, to use it -- that is, as long as you do so correctly. "The only _ is whether you're giving yourself a sense of false security," Dr. Gohara says. Indeed, as Dr. Wang also pointed out, when people choose increased SPFs, they may actually feel so protected by the product that they finally ignore proper sun protection. "When people use really high SPF products, they tend not to reuse, they tend to stay out in the sun much longer, and they don't use other protective measures such as clothing and hats," he says. Regardless of any increase in protection that a high SPF may or may not offer, one thing is certain: It doesn't give your body a free pass from sunburns, aging, or cancers, and it doesn't protect you from those things for any greater length of time than the lower SPF options. Both Dr. Wang and Dr. Gohara emphasized that, no matter what the SPF is, it's important to reapply your sunscreen every two hours. What rays can cause skin cancer according to the text?
UV UVA UVB UVA&UVB