Beauty is only a superficial sign of health, Beauty's main function is simply FOR attraction, the more attractive you are the more likely the opposite sex will mate with you. It's that simple.
Beauty really doesn't have a lot to do with health, there are lots of beautiful people with lots of "unseen" genetic and other serious health problems. Fact is, although from an evolutionary standpoint it may indicate health, it does so very badly compared to scientific knowledge we have now. It's very superficial health information.