Sericin Protein

Overview

Sericin is one of the two main proteins in silk. Silkworm cocoons are made of an inner fiber (fibroin) glued together by an outer protein (sericin). When silk is processed for textiles, the sericin is washed off as a waste product. That waste turned out to be a beautiful cosmetic ingredient.

In DIY supply, sericin comes as a clear-to-pale-yellow liquid (typically 1-5% active) or as a cream-coloured powder. Some suppliers sell it pre-hydrolyzed (smaller peptides); others sell it intact (larger protein, slightly different feel).

The key thing to know: sericin and hydrolyzed silk protein are different ingredients. Hydrolyzed silk is mostly the inner fibroin, broken down. Sericin is the outer glue protein, separate. Both come from silkworms, both are silky-feeling, but sericin is famous for water-binding — it can hold around 50 times its weight in water — while fibroin is famous for smooth film. Many premium formulas use both.

Shelf life is 1-2 years stored cool and dark. Liquid form benefits from refrigeration after opening.

Sericin is animal-derived. For vegan brands, use plant-protein alternatives.

What it does in a formula

Sericin is primarily a humectant film-former. The amino acid profile is heavy on serine, glycine, and aspartic acid — all small, hydrophilic amino acids that bind water aggressively at the skin surface.

The result on skin: a smooth, plump, slightly tightening feel as the water-binding film forms. On hair: a cuticle-smoothing film with extra moisture retention, particularly useful in dry climates or after chemical treatments.

Sericin also contributes a small antioxidant effect from the tyrosine fraction and a mild brightening reputation from melanin-binding activity. Both are subtle.

How to use

Add to the water phase or to the cool-down (below 40 C). High heat above 60 C for extended periods can denature the protein and reduce the water-binding effect.

Usage rates by product type (liquid form, ~3% active):

• Premium face serums: 3-8%
• Face creams (luxury): 2-5%
• Eye creams: 2-5%
• Hair masks and leave-ins: 2-5%
• Setting and styling sprays: 2-5%
• Body lotions (luxury): 1-3%
• Sheet mask essence: 2-5%

For powder form, divide percentages by 10-20 — sericin powder is highly concentrated.

Best for / Worst for

Best for: premium and luxury positioning, “second-skin” hydrating formulas, post-treatment skincare (after acids, retinol, procedures), dry-climate moisturizers, sheet masks and essences, post-chemical hair treatments.

Worst for: vegan-positioned brands (silk-derived), budget formulas, oil-only anhydrous products, formulas that already use hydrolyzed silk at high rates (overlap without enough differentiation).

Common pitfalls

Vegan claim. Sericin is animal-derived. For vegan brands, use plant proteins (rice, oat, pea, quinoa).

Confusing with hydrolyzed silk. Different ingredients, different roles. Both can appear in the same premium formula.

Adding too hot. Above 60 C the protein denatures. Add at cool-down.

Expecting fibroin-style silky finish. Sericin is plumper and more “water-cushioned” than fibroin. The mouthfeel is different. If you want the slick fibroin feel, use hydrolyzed silk too.

Microbial growth. Like all proteins, a feast for bacteria. Preserve broad-spectrum.

Substitutes

• Hydrolyzed silk protein — same plant, fibroin instead of sericin, silkier feel.
• Sodium hyaluronate — vegan, similar water-binding, different feel.
• Hydrolyzed rice protein — vegan, much cheaper, similar role.
• Beta-glucan — vegan, water-binding and soothing.
• Hydrolyzed pea protein — vegan, similar humectant character.