“Algin”: what is its role and value in cosmetics?

Key points to remember about “Algin”.

Sodium alginate is a polysaccharide extracted from brown algae.
It has gelling, thickening and stabilising properties and belongs to the cosmetic family of texture agents.
Sodium alginate forms a protective film on the surface of the skin, which limits dehydration and improves skin comfort.
It can also be used to encapsulate active ingredients, in order to release them more effectively into the skin.
Several studies also suggest that sodium alginate has anti-inflammatory and wound-healing effects.
Sodium alginate has an excellent tolerance profile, with no known contraindications.

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Focus on sodium alginate.

“Algin”, more widely known as sodium alginate, is a naturally occurring polysaccharide extracted from certain brown seaweeds (Phaeophyceae), such as the genera Laminaria, Ascophyllum or Macrocystis. It is obtained by an alkaline extraction process from the cell walls of these seaweeds, which are rich in alginic acids. Once purified and neutralised, this alginic acid is converted into the sodium salt, yielding a water-soluble powder that is commonly used in cosmetics, but also in the pharmaceutical and food sectors as an excipient or texturising agent.

Physicochemical characteristic	Values
Chemical formula	(C₆H₇O₆Na)ₙ
Names	Algin, sodium alginate
Aspect	White to yellowish powder
Molar mass	Variable (≈ 10⁴ to 10⁶ Da depending on the degree of polymerisation)
Dosage	Generally 0.1% to 5% in cosmetic formulations
Solubility	Soluble in water, insoluble in organic solvents

Physico-chemical properties of sodium alginate.

From a chemical perspective, sodium alginate is composed of a succession of mannuronic acid and guluronic acid units, arranged in blocks of varying length along the polymer chain. This structure gives “Algin” specific physico‑chemical properties, notably its ability to interact with water and certain ions, such as calcium, forming three‑dimensional networks. Not ionic in the strict sense but negatively charged in solution, sodium alginate is stable over a wide pH range and compatible with many ingredients. Its composition and structure may vary depending on the algal species used and the extraction conditions.

Structures chimiques de l’acide mannuronique et de l’acide guluronique — Chemical structures of mannuronic acid and guluronic acid
Source: SIONKOWSKA A. & al. State of innovation in alginate-based materials. Marine Drugs (2023).

Why use “Algin” in cosmetics?

Sodium alginate is particularly valued in cosmetics for its gelling and thickening properties. In the presence of water, this marine-derived polymer is able to form soft, homogeneous gels, which makes it possible to structure a wide range of textures, from creams and lotions to masks. Used as a gelling agent, it improves the stability of formulations and gives them a more pleasant application, with a fresh, lightweight feel. This is why sodium alginate is included in the composition of many cosmetic products, where it also acts as a stabiliser and cohesion agent.

Beyond its texturising role, “Algin” forms on the surface of the skin a supple but non-occlusive film, which limits transepidermal water loss and helps maintain hydration of the stratum corneum. Indeed, similarly to the skin’s natural hydrolipidic film, the film formed by sodium alginate acts as an interface between the skin and the environment, helping to reduce the impact of external aggressions. This property explains the use of sodium alginate in products designed for dehydrated skin. Furthermore, its biocompatibility and natural origin make it a particularly sought-after ingredient in eco-responsible formulations, notably in the form of sodium alginate powder.

≈ 9,000 times its weight

Water absorption capacity of sodium alginate.

Sodium alginate is also used as an active ingredient delivery system. Thanks to its polymeric structure, it can encapsulate certain molecules and enable their gradual release, thereby optimising their availability at the skin level. This property is particularly useful for delivering to the skin active substances which, on their own, have difficulty crossing the skin barrier, whether because of their molecular weight being too high or their hydrophilic nature.

Finally, several studies in the biomedical field have shown that sodium alginate could be useful for promoting wound healing of the skin. In the form of hydrogels, it is able to maintain a moist environment conducive to healing, while absorbing exudates and protecting the wound. Studies show that sodium alginate can promote re-epithelialisation and angiogenesis, that is, the formation of new blood vessels. More interestingly, some work indicates that alginate-based structures can interact with the local immune system, in particular with macrophages, cells that are involved during the inflammatory phase of healing.

A recent study on a hydrogel combining sodium alginate and bioglass has highlighted a specific mechanism: this type of material promotes the polarisation of macrophages towards an M2 phenotype, which is associated with an anti-inflammatory and reparative response.

These “repair” macrophages will then recruit other essential cells, such as fibroblasts, involved in the synthesis of extracellular matrix components, and endothelial cells, required for the formation of new blood vessels. These different processes contribute to accelerating skin regeneration. These data suggest that sodium alginate, beyond its role as a scaffold, can modulate the inflammatory response. Although these results come from experimental models, they open up interesting prospects for the use of sodium alginate in wound-healing treatments.

Are there any risks associated with sodium alginate that you should be aware of?

Sodium alginate has a well-established safety profile, extensively documented in the scientific literature. Biocompatible, biodegradable and non-toxic, it has long been used in the food, pharmaceutical and cosmetic fields. When applied topically, it is considered well tolerated by all skin types, including sensitive skin, children, pregnant women and individuals with skin conditions. Its action remains mainly superficial, which limits the risk of systemic effects or deep reactions.

Several clinical studies confirm this good tolerability. For example, a trial conducted in 80 patients with atopic dermatitis evaluated the use of a sodium alginate–based reparative mask as an adjunct to a topical corticosteroid. The group that used alginate in combination showed fewer adverse effects (2.5% versus 22.5%) and a more pronounced improvement in symptoms, with a significant reduction in clinical scores and relapse rate.