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Proteins & peptides

Collagen (topical)

Also listed as hydrolyzed collagen, soluble collagen

In creams, collagen is a moisturizer. The molecule is far too large to enter skin, so it cannot replace or rebuild your own collagen.

No real evidence

What it is

Collagen is the main structural protein of the dermis. In skincare it is usually animal- or fish-derived collagen or smaller hydrolyzed fragments. An intact collagen molecule weighs around 300,000 daltons, while molecules much above 500 daltons don't get through the skin's outer layer, so collagen stays on the surface.

There it works as a humectant and film-former: it holds water and leaves skin feeling smoother and plumper for a while. That is real but temporary, and it's the same job glycerin or hyaluronic acid does. 'Collagen' serums that claim to boost your own collagen rely on other actives, such as retinoids, vitamin C or peptides, for any effect. Oral collagen supplements are a separate question with their own evidence.

How strong is the evidence?

No real evidence

No credible evidence shows that collagen applied to skin increases skin collagen or firmness; the size limit on skin penetration is basic physiology. Its moisturizing effect is real but modest and short-lived.

What it's used for, checked

Builds or replaces skin collagen

False

Far too large to penetrate; your collagen is made by fibroblasts deep in the dermis.

Moisturizing and smoothing

Holds up

Holds water on the surface, like other humectants.

Firming and wrinkle reduction

Unproven

Any plumping is temporary surface hydration.

Who should be careful

  • Well tolerated. Most cosmetic collagen is animal- or fish-derived, which matters if you avoid animal products.

The studies

Every citation is checked against its PubMed record.

  1. The 500 Dalton rule for the skin penetration of chemical compounds and drugs.
    Bos JD, Meinardi MM · Experimental Dermatology · 2000 · Review

    Argues that a compound must weigh under about 500 daltons to pass through the skin's outer layer, based on the size of known contact allergens and of the drugs that work topically or through transdermal patches.