from the age old curse known as wrinkles. photo aging comes from exposure to the sun's radiation, and specifically uva radiation. it's not the uvb radiation has linked to cancer. you can see it in these photos. this is the hand of a person with no skin damage, and this is someone with severe photo aging. in a study with 900 patients, those who used sunscreen daily over a 4 1/2 year period were 24% less likely to see these kinds of progressive changes. and doctors say this message will resonate with their patients. >> every patient, we try to tell them to use sunscreen, and believe it or not, just the message of preventing skin cancer doesn't always get through to people. so i'm hoping that maybe vanity will weigh out in this case. >> the rules for sunscreen, she says, are simple. >> you want to look for an spf of about 30. you want it to be broad spectrum, which means it covers