Polyhydroxystearic Acid (PHSA) is frequently seen in makeup, lotions, and sunscreens. This common component often has a confusing name for the average user. This guide explains its chemical nature and established safety profile in consumer applications.
Defining Polyhydroxystearic Acid
Polyhydroxystearic Acid (PHSA) is a polymer, meaning it is a large molecule made up of many smaller, repeating units. The chemical building block for this polymer is 12-Hydroxystearic Acid, a modified fatty acid. This smaller molecule is most commonly sourced from the natural, vegetable oil derived from the castor bean plant.
Manufacturers link multiple units of 12-Hydroxystearic Acid together into long chains, forming a high-molecular-weight material. The resulting fatty acid polymer is physically characterized as a soft, pliable wax or a light yellow, semi-solid material. PHSA is a plant-derived ingredient used extensively in cosmetic formulation.
Primary Function in Consumer Products
The presence of Polyhydroxystearic Acid in a product is primarily due to its unique functional properties as an emulsifier and stabilizer. In cosmetic formulations that contain both oil-based and water-based components, such as creams and lotions, PHSA acts to hold these opposing liquids together. This emulsifying action prevents the ingredients from separating, which maintains the product’s uniform texture and ensures its long-term stability.
Beyond stabilizing emulsions, the compound is highly valued for its ability to function as a pigment dispersant. In color cosmetics like foundations and lipsticks, PHSA ensures that the color particles are distributed evenly throughout the product base, leading to a cohesive and smooth application. This function is particularly important in mineral sunscreens, where it is used to coat active ingredients like zinc oxide or titanium dioxide.
By coating these mineral filters, PHSA helps them spread uniformly across the skin, which enhances the product’s Sun Protection Factor (SPF) performance. This action also helps to mitigate the unwanted white or chalky cast that mineral sunscreens can otherwise leave behind. Additionally, due to its waxy nature, PHSA provides a secondary benefit as an emollient, creating a smoother feel and improving the texture of the overall formula.
Safety Profile and Regulatory Status
The safety profile of Polyhydroxystearic Acid is considered low-risk, largely because of its chemical properties as a high-molecular-weight polymer. This large size means there is a very low likelihood of the molecule being significantly absorbed into the skin or bloodstream.
The Cosmetic Ingredient Review (CIR) Expert Panel, a group that assesses the safety of cosmetic ingredients, has concluded that PHSA is safe for use in cosmetics under current practices and concentrations. The highest reported concentration of use in products is approximately 14.2% in lipsticks, a product category where incidental ingestion is possible.
Toxicological assessments, including Human Repeated Insult Patch Tests (HRIPT), have demonstrated that PHSA is generally non-irritating and non-sensitizing, even when tested undiluted on human skin. This makes it well-suited for use in products designed for sensitive skin. It is also often cited as non-comedogenic, meaning it is not likely to clog pores.
Similar fatty acid derivatives are deemed safe for use in applications like consumer food packaging by bodies such as the European Food Safety Authority (EFSA). The low toxicity profile of these materials, coupled with the CIR Panel’s positive assessment, provides confidence in the safety of Polyhydroxystearic Acid as a widely used cosmetic ingredient.