Simon's study shows that UVA sunlight is absorbed by urocanic acid, a natural molecule made by the outermost skin cells. The sunlight chemically changes urocanic acid and causes it to create within the cells a type of oxygen free radical, a highly active molecule that can be damaging to cells. This oxygen radical, said Simon, ''degrades collagen and elastin, which are the major molecules that make up the skin. By degrading collagen and elastin, he said, ''you decrease the elasticity of the skin. People should be covered more of the time they are outside.
Hats are a good idea.
Simon said he allows his family ''reasonable exposure'' to the summer sun. People don't need to totally avoid the beach or pool, he said. They should be ''respectful, but not fearful of the sun.