What Exactly Is Polyhydroxystearic Acid?

2026-04-07

What Exactly Is Polyhydroxystearic Acid?

Polyhydroxystearic acid, commonly abbreviated as PHA, is a synthetic, oil-soluble polymer derived from castor oil or hydroxystearic acid. Despite the long name, its function is fairly straightforward: it acts as a dispersant and emulsifier in cosmetic formulas.

If you have ever used a mineral sunscreen or a liquid foundation that stayed smooth and didn’t separate, PHA was likely part of the formula. It is not a glamorous ingredient, but it solves a real problem. Many fine particles used in cosmetics—such as zinc oxide, titanium dioxide, or color pigments—tend to clump together. PHA coats each particle, preventing aggregation and helping them spread evenly. This results in better coverage, fewer application issues, and a more Stable product over time.

Common Uses in Cosmetics

Mineral Sunscreens

This is where PHA is most frequently used. Mineral sunscreens rely on zinc oxide and titanium dioxide to block UV rays, but these particles Naturally stick to one another. PHA disperses them, which reduces the heavy white cast often associated with mineral formulas. It also improves the uniformity of the SPF layer on the skin, making the sunscreen more effective without feeling overly thick.

Foundations and Color Cosmetics

Liquid foundations, concealers, and tinted moisturizers contain pigment particles that tend to settle over time. PHA keeps these particles suspended, so the product remains consistent from the first use to the last. It also contributes to better wear time and a more natural-looking finish.

Water-in-Oil Emulsions

PHA is an effective emulsifier for water-in-oil systems, where tiny droplets of water are dispersed in an oil phase. This type of emulsion feels richer and more moisturizing than standard oil-in-water lotions. It is commonly found in thicker creams, balms, and some sunscreens.

Clean Beauty Formulations

As many brands move away from silicones and PEG-based emulsifiers, PHA has become a popular alternative. It is mild, plant-derived, and compatible with a wide range of natural oils and butters. In so-called “clean” beauty products that still require reliable performance, PHA often plays a key role.

Safety Notes

PHA is considered very safe for topical use. It is non-irritating, non-sensitizing, and non-comedogenic. The Cosmetic Ingredient Review panel has approved it for use in cosmetic products, and it appears in formulas designed for sensitive skin without issue.

One point worth noting: PHA is synthetic, but its raw material is castor oil, which is plant-based. Most commercially available versions are biodegradable and vegan-friendly, although strict users may want to verify the processing methods with individual suppliers. For the vast majority of consumers, this is not a concern.

Handy DIY Tips

For those making their own skincare products or working with cosmetic formulations, here are a few practical notes:

Dissolve PHA in the oil phase before combining with water. Gentle heating to around 70–75°C helps with dispersion.

In mineral sunscreen formulas, PHA is highly recommended. It significantly reduces the white cast and improves spreadability.

Used alone, PHA produces relatively fluid emulsions. For thicker textures such as butters or balms, it works well in combination with another emulsifier, such as polyglyceryl-3 polyricinoleate.

Typical usage rates range from 1% to 5% of the total formula, depending on the particle load.

Sourcing

PHA is not an expensive ingredient, but quality varies between suppliers. For small-batch or DIY use, retailers such as MakingCosmetics and Lotioncrafter offer reliable options. For commercial production, it is advisable to work with specialty ingredient distributors and request purity data and stability test results. Lower-cost versions may contain impurities that affect emulsion stability or produce an off odor.