It's a nature identical, biomimetic peptide that can do multiple good things to the skin:
First, it's an antioxidant that can protect skin from damaging free radicals.
Second, in-vitro (made in the lab, not on real people, so take it with a grain of salt) studies show that it has anti-glycation properties (glycation is the not-so-nice process that happens when we bombard our body with too much sugar that results in damaged body proteins and eventually in more wrinkles).
Third, also in vitro studies show that carnosine has collagen-boosing magic power.
And last, but not least an in vivo, made on real humans clinical study shows that carnosine is very effective against the damages caused by infrared (IR) radiation. (source)