A net. It holds the water in, and that's the glow.

Collagen is far too big a molecule to get through your skin, so the collagen in your cream never reaches the cells that make your own. What it does is sit on top and form a film that traps moisture underneath. That's the plump, glowy face you wake up to after a collagen mask, and it's real. It just isn't new collagen.

So not nothing: it's a good hydrator, and should be priced like one. The newer collagen tripeptides (Tripeptide-29 on the label) are small enough to get in, but the human evidence is one 22-person study, so treat them as a bonus, not the reason to spend. Your real collagen budget goes on retinoids and sunscreen.