Chitosan

Chitosan is a biopolymer made from chitin, the structural material in crustacean shells and fungal cell walls. In skincare it forms a thin film on skin and hair, and in formulation science it is one of the most studied materials for building carrier particles.

At a glance

• Evidence level A. Published research on the ingredient itself.
• What it is. A long-chain polysaccharide, one of the few natural polymers that carries a positive charge in water.
• What it does. Forms a flexible film; binds to negatively charged surfaces and polymers; used to build carrier structures.
• Caution. Derived mainly from shellfish. Ask about the source if that matters to you.

What it is

Chitin is the second most abundant natural polymer after cellulose. Removing part of its acetyl groups turns it into chitosan, a chain of glucosamine units. The share removed, called the degree of deacetylation, and the chain length vary by grade, and they change how the material behaves.

Commercial chitosan is produced mainly from the shells of shrimp and crab, a by-product of seafood processing. Grades from fungal sources also exist. The source of any given grade is set out in its supplier's specification.

What it does in skincare

Film former. Chitosan dissolves in slightly acidic water and dries to a flexible, breathable film. That is its oldest cosmetic use: in hair styling products and conditioners, where the positively charged polymer binds to the negatively charged surface of hair, and in skincare, where it leaves a smooth, conditioned feel.

Carrier material. Because it is positively charged, chitosan pairs with negatively charged polymers such as alginate or hyaluronic acid. Formulation scientists use that attraction to build particles and shells that hold an active ingredient. One well-studied method, layer-by-layer assembly, builds a shell one thin layer at a time by alternating oppositely charged materials. How carrier families compare: carrier systems compared. How encapsulation works in general: how encapsulation works. The wider category: delivery systems.

Evidence

The studies below describe the ingredient itself.

Rinaudo reviewed the chemistry, properties and applications of chitin and chitosan in 2006, and Kumar published an earlier broad review of their applications in 2000. Aranaz and colleagues reviewed cosmetic and cosmeceutical uses specifically in 2018, covering film formation, hair care and skin care.

Decher described layer-by-layer assembly of oppositely charged polymers in 1997, the basis for much of the later work on multi-layer shells. Bernkop-Schnürch and Dünnhaupt reviewed chitosan-based delivery systems in pharmaceutical research in 2012.

Much of the carrier literature comes from drug delivery. It shows what chitosan can do as a building material under the conditions of each study.

Use and caution

• Chitosan is widely used in cosmetics and is rarely associated with irritation in the literature.
• People with a shellfish allergy often ask about chitosan. Shellfish allergy is usually a reaction to shellfish proteins, and how much protein a chitosan grade retains depends on its purification. That question belongs with your allergist and the product's manufacturer.
• Chitosan from crustacean shells is an animal-derived ingredient.
• If your skin is reactive, patch test first. See patch testing and declared allergens.

In Vegalab products

The Hyaluronic Skin Repair NanoSerum sealed vial set lists chitosan in its ingredient declaration.

• Hyaluronic Skin Repair NanoSerum, Sealed Vial Set

Reading a full declaration: how to read an ingredient list.

Related ingredients

• Hyaluronic acid, a negatively charged polysaccharide
• Delivery systems, carriers in skincare
• Silk proteins, another film-forming biopolymer
• Related concern: hydration and barrier
• All entries: ingredient library

References

1. Rinaudo M. Chitin and chitosan: properties and applications. Prog Polym Sci. 2006;31(7):603-632.
2. Kumar MNVR. A review of chitin and chitosan applications. React Funct Polym. 2000;46(1):1-27.
3. Aranaz I, Acosta N, Civera C, et al. Cosmetics and cosmeceutical applications of chitin, chitosan and their derivatives. Polymers (Basel). 2018;10(2):213.
4. Decher G. Fuzzy nanoassemblies: toward layered polymeric multicomposites. Science. 1997;277(5330):1232-1237.
5. Bernkop-Schnürch A, Dünnhaupt S. Chitosan-based drug delivery systems. Eur J Pharm Biopharm. 2012;81(3):463-469.