Does collagen in a cream reach the collagen in my skin?

No. The fragments are far too large for an intact surface layer to pass in any quantity, and dermal collagen is built on site out of amino acids delivered by the blood.

What does hydrolysed actually change?

The size. Cutting the protein into peptides is what makes it dissolve and spread, which turns an unusable raw material into a usable humectant.

What about the studies on collagen peptides?

Most of that research is about ingestion. It is a different route to a different place, and whatever one makes of it, it is not evidence about a cream.

No. It is animal-derived — usually bovine, porcine or marine — and the ingredient name does not tell you which one.

Is it worth paying more for?

As a humectant it does what humectants do. Liking the finish is a fair reason to buy it; the word collagen on the front of the box is not one.

Hydrolyzed Collagen — Ingredient Guide

How it works

Collagen in the body is a long triple helix, and as a cosmetic raw material that is a problem: it is enormous, it dissolves badly, and what it mostly does on skin is sit there. Hydrolysis — with acid, alkali or an enzyme — cuts it into a mixture of shorter peptides and free amino acids. That is the whole of the difference between this ingredient and the intact protein, and it is the point of it.

The fragments dissolve properly in water, spread as a thin even film rather than a tacky layer, and carry the water-binding groups that make them humectants. On skin the result is a surface that holds moisture a little better, feels smooth, and looks briefly fuller as the film dries down over it. That effect is real, it is measurable, and it is a surface effect.

The evidence

Two claims travel with this ingredient and only one of them survives contact.

The first is that it hydrates and conditions the surface. It does, unremarkably, in the way glycerin and the other water-binding ingredients do, with a different feel to it.

The second is that it replaces or rebuilds the collagen in your skin. It does not. Even hydrolysed, the bulk of the fragments are far heavier than what an intact surface layer lets through, and the body does not take a peptide out of a cream and reassemble it into dermal collagen — that fibre is built on site by fibroblasts, out of amino acids delivered by the blood. The clinical literature people reach for when defending collagen is, in the main, research on swallowing it. Whatever one concludes about that work, it is a different route to a different place, and quoting it on a jar is a category error.

Suitability

Suits most skin as a humectant, and sits comfortably under makeup
Animal-derived — bovine, porcine or marine — and the INCI name does not say which
Worth reading the source if you avoid animal ingredients; an allergy question belongs with a clinician rather than with an ingredient list
No reason to expect more of it than of any other water-binding ingredient in the same place in a routine

Concentration

No figure. Hydrolysates differ enormously in average fragment size and the supplier's specification matters far more than the percentage on a box — a heavily cut hydrolysate and a lightly cut one are not the same material. And there is no threshold at which a surface humectant becomes a dermal one.

Conflicts & combinations

Nothing conflicts with it. Like every humectant it works better with something over it: a humectant alone in dry air can leave skin no better off than it started, and the emollient or occlusive layer on top is what makes the water it gathered stay gathered.