On labels, they appear as Hydrolyzed Silk, Serica, or Hydrolyzed Sericin, and the name suggests a precious active ingredient. Silk peptides are something specific and do something specific: it is worth knowing what that is, because it is not what the name suggests.
Silk peptides are fragments obtained by breaking down the two proteins in the silkworm cocoon. They are not signal peptides: they do not communicate with fibroblasts or stimulate collagen production. They work on the surface, where they form a thin film that retains water and makes the skin feel smooth. The effect is immediate and sensory, not structural.
Article written by Elisa Avalle, founder of LeLang Skin Care and a specialist in dermocosmetics. Cover image generated with the support of artificial intelligence.
[INDICE:h2]
Where they come from
The silkworm cocoon is made of two proteins. Fibroin is the actual thread, the one that becomes fabric. Sericin is the gummy substance that holds the thread together, and in the textile industry it is removed during the degumming stage: for years it was a processing by-product; today it is a raw material.
Both, as they are, are proteins that are too large to do anything on intact skin. To use them in a cosmetic product, they are hydrolyzed, meaning they are broken down into shorter fragments using acids or enzymes. The result is a mixture of peptides and free amino acids that remains in solution and spreads evenly over the skin.
Why the skin recognizes them
The composition of silk is unusually simple: glycine, alanine, and serine alone account for the vast majority of the amino acids in fibroin.
Serine is also one of the components of the Natural Moisturizing Factor, the natural moisturizing factor of the stratum corneum, where free amino acids are the most abundant fraction. This is why these hydrolysates have good affinity with the skin barrier and high tolerability.
That is also the limit of the reasoning, though. Resembling what the skin already has makes an ingredient well tolerated and useful on the surface; it does not turn it into an active ingredient that modifies the dermis.
What they do, honestly
- They retain water on the surface. The film they form reduces evaporation from the stratum corneum, producing an immediately noticeable moisturizing effect.
- They make the skin feel smooth to the touch. This is the most noticeable effect, and it is not a minor detail: slip is one of the reasons they are used.
- They even out the reflection of light. A smoother surface produces a more uniform complexion, with that slightly opalescent result known as the soft-focus effect.
- They improve the formula’s sensory feel. In cleansers, masks, and hair products, this is often their main function.
Sericin also has a body of literature on its antioxidant and moisturizing properties, much of which comes from in vitro studies and animal models. It is an interesting and still-evolving area of research, not proof of efficacy on human facial skin.
What they do not do
They do not stimulate collagen production, reduce expression lines, or work on cell renewal. If a product markets silk as an anti-aging active ingredient, it is using the appeal of the raw material in place of a mechanism of action.
That is the key difference compared with biomimetic peptides, which are molecules built in a laboratory with a precise sequence, chosen to transmit an equally precise signal to fibroblasts.
| Comparison | Silk peptides | Biomimetic peptides |
| Origin | Hydrolysis of a natural protein | Synthesis, defined sequence |
| Where they act | Stratum corneum, on the surface | Deeper layers of the epidermis |
| Mechanism | Moisturizing film | Signal to fibroblasts |
| Timing | Immediate | Four to eight weeks |
| What they work on | Softness, comfort, radiance | Firmness, wrinkles, elasticity |
They are two tools for two objectives, not alternatives to one another. In well-designed formulas, they coexist, and each plays its part.
How to read them on the label
The INCI names to look for are Hydrolyzed Silk, Serica, Hydrolyzed Sericin and Silk Amino Acids. They are generic: they do not indicate which of the two proteins is used or how extensive the hydrolysis is, and those are precisely the two factors that change the ingredient’s behavior.
As always, the position in the INCI says more than the name: towards the bottom of the list, we are talking about fractions of a percentage point, an amount that affects sensorial properties more than anything else.
Animal origin and alternatives
Two practical limitations should be mentioned. First: silk is of animal origin, so its hydrolysates are not suitable for vegan formulas. In products that exclude animal ingredients, they are replaced with hydrolysates of rice, oats, wheat or soy, which have the same film-forming and humectant function.
The second: reactions are rare, but anyone with a known sensitivity to silk proteins is right to read the INCI before buying. The same applies to anyone with highly reactive skin, where every plant or animal protein deserves to be patch-tested on a small area.
A cosmetic acts on the surface and superficial layers of the skin and does not treat any clinical condition, according to EC Regulation 1223/2009 and EU Regulation 655/2013. For a skin reaction that does not resolve, consult a doctor.
When it makes sense to look for them
They make sense in a cleanser, a mask, a cream you want to feel comfortable, and hair products, where the film can be seen and felt. They make sense on dry or tight-feeling skin, alongside a moisturising system built around hyaluronic acid, urea and amino acids.
They make no sense if what you are looking for is a way to address signs of ageing: in that case, the label to look for is a different one, namely peptides with a number next to them.
If you have a product at home and want to understand what is really in it, LeLang partner pharmacists will read the INCI with you.
15-minute free consultation with the founder
Want to understand which active ingredients your skin really needs? Book a free virtual skincare consultation with Elisa Avalle, founder of LeLang.
Frequently asked questions
Do silk peptides help against wrinkles?
No. They do not transmit signals to fibroblasts or affect collagen production. What they do is make the surface smoother and more even, and on dry skin this can make fine lines appear less pronounced while the product is on the skin. It is an optical effect, not a structural result.
What is the difference between fibroin and sericin?
Fibroin is the silk thread, while sericin is the glue that holds it together. Fibroin hydrolysates are mainly film-forming; sericin also has literature supporting hydrating and antioxidant activity, largely based on in vitro studies. The distinction is not always apparent on the label.
Are silk peptides vegan?
No, they are of animal origin. In vegan formulas, the same function is provided by hydrolysates of rice, oats, wheat or soy.
Are they suitable for sensitive skin?
Generally, yes: they are highly well tolerated and their composition is close to that of the amino acids already found in the skin. However, anyone with a known sensitivity to silk proteins should avoid them, and with highly reactive skin, it is always best to test on a small area first.
Are they the same as the peptides found in anti-aging serums?
No, and the common name is misleading. Anti-aging peptides are synthetic molecules with a precise sequence, such as tripeptides or hexapeptides, designed to send a message to cells. Silk peptides are heterogeneous fragments of a natural protein, and their work ends at the surface.
Sources for this article
- Padamwar M.N., Pawar A.P. (2004). "Silk sericin and its applications: a review". Journal of Scientific and Industrial Research, vol. 63, pp. 323-329.
- Literature on the amino acid composition of silk proteins: glycine, alanine and serine make up the clearly predominant fraction of fibroin.
- Literature on the Natural Moisturizing Factor: free amino acids, derived from the degradation of filaggrin, are the most abundant component of the natural moisturizing factor in the stratum corneum.
- Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products.
- Commission Regulation (EU) No 655/2013, common criteria for the justification of claims relating to cosmetic products.
On the website: Peptides for the skin · Amino acids in cosmetics · Skin barrier · Ingredient fact sheet: peptides
