Stearoxyhydroxypropyl Methylcellulose — INCI reference

What it is

Stearoxyhydroxypropyl Methylcellulose (also listed in CosIng as Hydroxypropyl Methylcellulose Stearoxy Ether) is a hydrophobically modified cellulose derivative formed by reacting stearyl glycidyl ether with hydroxypropyl methylcellulose. The introduction of stearyloxy (C18 alkyl ether) groups onto the cellulose backbone imparts amphiphilic character, enabling the ingredient to function as a viscosity modifier even at low concentrations (typically 0.1–1.0% w/w). Formulations remain water-soluble when stearyloxy group content stays below approximately 0.6% by weight. The ingredient exhibits thixotropic flow behavior, meaning viscosity decreases under shear and recovers at rest, which is beneficial for pump-dispenser and squeeze-tube cosmetics. It is used in skin creams, lotions, serums, sunscreens, hair care, and makeup products to improve texture, spreadability, and phase stability.

Safety & warnings

No significant safety concerns have been identified for this ingredient. EWG Skin Deep rates the related Hydroxypropyl Methylcellulose Stearoxy Ether as low hazard (score 1). No GHS hazard classifications have been established. No known allergens, irritants, or comedogenic properties are documented. Oral, dermal, and inhalation toxicity data have not been formally determined, consistent with its use at low concentrations as a polymer excipient.

Origin & sourcing

Derived from cellulose, a natural plant polysaccharide, through sequential chemical modification. Cellulose is first etherified with methyl and hydroxypropyl groups to yield hydroxypropyl methylcellulose (HPMC), which is then reacted with stearyl glycidyl ether to introduce long-chain stearyloxy substituents. The final product is a semi-synthetic polymer not found in nature.

History

Hydroxypropyl methylcellulose has been used in pharmaceuticals and cosmetics for decades. The stearoxy ether derivative was developed to combine the water-thickening properties of HPMC with improved emulsification and amphiphilic character from the fatty stearyloxy chains. It is listed in the EU CosIng database (reference 56831) as a permitted cosmetic ingredient with a viscosity-controlling function.

Questions everyone asks

What does Stearoxyhydroxypropyl Methylcellulose do in a formula?

It functions primarily as a viscosity-controlling agent, thickening water-based formulations and improving the texture and stability of creams, lotions, and serums. Its amphiphilic structure also helps stabilize emulsions.

Is this ingredient natural or synthetic?

It is semi-synthetic. The cellulose backbone comes from plant sources, but it undergoes chemical modification (methylation, hydroxypropylation, and reaction with stearyl glycidyl ether) to produce the final ingredient, which does not occur in nature.

Is Stearoxyhydroxypropyl Methylcellulose safe for sensitive skin?

Based on available data it is considered low hazard with no known allergens or irritants identified. It appears in EU CosIng as a permitted cosmetic ingredient with no documented restrictions, and EWG rates the equivalent INCI name at its lowest concern level.

At what concentrations is it used in cosmetics?

It is typically effective at 0.1–1.0% by weight of the total formulation, with the lower end of that range (0.1–0.5%) often sufficient to achieve the desired viscosity and thixotropic flow behavior.