Polyhydroxystearic Acid is a high-performance, plant-derived dispersing agent and thickener primarily utilized to stabilize mineral UV filters and pigments. This polyester ensures an even distribution of particles in oil-based formulas, significantly enhancing SPF efficiency and the aesthetic spreadability of sunscreens and color cosmetics.
- INCI Name:
- Polyhydroxystearic Acid
- Chemical/Scientific Name:
- 12-hydroxystearic acid, homopolymer
- Common Aliases:
- Polyhydroxystearate, Hydroxystearic acid polymer
| Category: | Stabilizers |
| Source Origin: | Vegetable (derived from Ricinus Communis Seed Oil) |
| Comedogenic Rating: | 0 |
| Primary Industries: | Sun Care, Color Cosmetics, Luxury Skincare |
| Solubility: | Lipophilic (Oil-soluble) |
At a Glance: Properties & Effects
| Texture Enhancement: | |
| Formula Stability: | |
| SPF Boosting: | |
| Irritation Risk: |
Primary Benefits:
- Prevents the clumping (flocculation) of mineral particles like Zinc Oxide.
- Improves the sensory feel of heavy oil-based formulations.
- Increases the uniformity of UV protection films on the skin.
- Reduces the white cast of physical sunscreens by ensuring fine particle dispersion.
Potential Risks:
- None identified for topical cosmetic use.
Biological Action & Cosmetic Profile
Polyhydroxystearic Acid functions through steric stabilization, a process where the polymer chains coat individual pigment particles to create a physical barrier. In sunscreens containing Titanium Dioxide or Zinc Oxide, these mineral particles naturally tend to agglomerate, which creates gaps in the UV protective film. By keeping these particles separated, this ingredient ensures the active minerals remain perfectly dispersed, which maximizes the SPF value and prevents the “patchy” protection often seen in poorly formulated mineral sunscreens.
As a texture-enhancing agent, this polyester reduces the surface tension of the oil phase. Lowering this tension allows for a significantly higher load of solids (pigments or powders) without making the final product feel overly thick or greasy. Formulators rely on this property to create “weightless” makeup and fluid-like sunscreens that maintain high coverage or high protection levels. The ingredient’s structure, typically derived from the fatty acids found in Ricinus Communis Seed Oil, gives it excellent biocompatibility and a silky, non-tacky finish.
Film-forming capabilities further distinguish this ingredient from basic oils. Upon application, it aids in creating a thin, water-resistant layer on the skin’s surface. This secondary benefit is particularly useful in “sport” or “water-resistant” sunscreens, as it helps the active ingredients adhere to the skin more effectively during perspiration or aquatic activities. While it provides a protective barrier, the polymer’s size prevents it from penetrating the stratum corneum, ensuring its action remains purely functional on the skin’s surface.
Broader Applications & Origins
Vegetable-derived sources provide the raw materials for this polymer, specifically the hydroxystearic acid produced from castor oil. Its chemical relationship to Stearic Acid and Isostearic Acid makes it a familiar and compatible component within the lipid matrices of most emulsions. Beyond UV protection, it is an essential ingredient in high-pigment cosmetics, such as full-coverage foundations and liquid lipsticks, where it prevents color streaking and sedimentation during storage.
Routine Integration
Synergies:
- Zinc Oxide: Enhances dispersion and SPF efficacy.
- Titanium Dioxide: Maximizes coverage and reduces white cast.
- Iron Oxides: Ensures uniform color distribution in foundations.
- Emollients like Caprylic Capric Triglyceride: Improves spreadability and skin feel.
Clinical Consensus & Safety
The Cosmetic Ingredient Review (CIR) Expert Panel has assessed Polyhydroxystearic Acid as safe for use in cosmetics at concentrations typically ranging from 0.5% to 10%. Clinical evaluations demonstrate that it is non-sensitizing and non-irritating to both the skin and eyes. Because the molecular weight of the polymer is high, it is not absorbed into the bloodstream, making it an ideal choice for sensitive skin formulations. Dermatological consensus highlights its role as a functional necessity in mineral sunscreens, as properly dispersed UV filters are critical for preventing sun damage and subsequent skin cancers.
Is Polyhydroxystearic Acid natural?
Yes, this ingredient is typically derived from natural castor oil sources. It undergoes chemical processing to form a polyester, but it is widely accepted in “clean” and “natural” beauty standards as a safe, plant-based functional ingredient.
Does it cause acne or clogged pores?
Polyhydroxystearic Acid has a comedogenic rating of 0, meaning it is highly unlikely to cause breakouts. Its primary role is to sit on the surface to manage pigments rather than sinking into the pores.
Why is it in my mineral sunscreen?
Without this ingredient, the mineral powders in your sunscreen would clump together, leaving some areas of your skin unprotected while others have too much. It ensures the sunscreen is effective, easy to apply, and looks transparent on the skin.