What Is Lactic Acid/Hydroxystearic Acid Copolymer?
Lactic Acid/Hydroxystearic Acid Copolymer is a man-made ingredient created by linking together two small building blocks: lactic acid, the well-known fruit-derived acid often used for gentle exfoliation, and hydroxystearic acid, a fatty acid that can be sourced from castor or other plant oils. When these two components are joined in a repeating chain, they form a copolymer that behaves differently than either acid on its own. First explored in the early 2000s as chemists searched for milder, more stable ways to deliver lactic acid’s skin benefits, the material soon found a place in cosmetics because it offers the skin-friendly feel of fatty acids with the conditioning touch of lactic acid.
The copolymer is typically made through a controlled heating process in which lactic acid and hydroxystearic acid are combined with a catalyst. The reaction causes the acids to link up, creating longer chains that are later purified to remove any leftover acids or catalyst residues. The result is a smooth wax-like substance that can be melted into creams or dispersed in water-based products.
You will most often see Lactic Acid/Hydroxystearic Acid Copolymer in moisturizers, anti-aging serums, sheet masks, leave-on treatments and certain soothing lotions. Formulators like it because it is easy to blend, it does not irritate sensitive skin as pure acids can, and it helps products feel elegant when applied.
Lactic Acid/Hydroxystearic Acid Copolymer’s Cosmetic Benefits/Uses
Its main role in skin care is skin conditioning, meaning it helps keep the surface of the skin soft, smooth and comfortable. By pairing the mild exfoliating action of lactic acid with the cushioning effect of a fatty acid, the copolymer supports a healthy skin barrier, improves moisturization and leaves a velvety finish that many users enjoy.
Who Can Use Lactic Acid/Hydroxystearic Acid Copolymer
This copolymer suits most skin types, including normal, dry, combination and sensitive skin, because it cushions the mild action of lactic acid with a fatty acid that comforts the barrier. Very oily or severely acne-prone skin may find richer formulas that contain it feel too heavy, though the ingredient itself is not known to be highly pore clogging.
The raw materials are typically produced by plant fermentation and castor-derived oils, so the ingredient is generally considered vegan and vegetarian friendly. Those who follow a strict lifestyle should still check with the brand to confirm that no animal by-products were used in its processing.
Current safety data show no issues for women who are pregnant or breastfeeding when the ingredient is used in normal cosmetic concentrations. That said this is not medical advice and anyone who is expecting or nursing should ask their doctor before adding new products to a routine.
The polymer form greatly reduces the photosensitivity sometimes seen with free lactic acid, but any gentle exfoliation can make skin slightly more reactive to sunlight. Daily SPF is still recommended. The ingredient plays well with most actives though pairing it with stronger acids or retinoids on the same night could increase the chance of irritation in very reactive skin.
Potential Side Effects/Adverse Reactions
Responses to topical Lactic Acid/Hydroxystearic Acid Copolymer vary from person to person. The effects below are potential outcomes and are not likely for the average user when the ingredient is correctly formulated and used as directed.
- Mild tingling or stinging especially on freshly cleansed or compromised skin
- Temporary redness or warmth that usually subsides within minutes
- Dry patches or light flaking if combined with other exfoliants too often
- Breakouts or clogged pores in individuals extremely prone to acne when used in rich, occlusive bases
- Allergic contact dermatitis in the rare event of a true sensitivity to one of the component acids
- Increased sun sensitivity if no sunscreen is applied during daytime use
If any of these effects persist or worsen stop using the product and seek advice from a healthcare professional.
Comedogenic Rating
Rating: 1 / 5
Lactic Acid/Hydroxystearic Acid Copolymer scores low because the lactic acid portion is non-comedogenic and the fatty acid portion is bound into a large polymer that does not penetrate deeply into pores. While hydroxystearic acid on its own can be mildly occlusive, once it is locked into the copolymer its ability to clog pores drops sharply. Laboratory data and anecdotal reports show few cases of congestion when the ingredient is used in lightweight bases.
Generally suitable for acne-prone or breakout-prone skin, especially in gels, lotions or serums that are not overly rich.
Keep in mind the final product’s texture, accompanying oils and overall formulation play a bigger role in pore clogging than this ingredient by itself.
Summary
Lactic Acid/Hydroxystearic Acid Copolymer acts primarily as a skin-conditioning agent, offering gentle surface smoothing from the lactic acid side while the hydroxystearic acid portion provides a soft, cushioned feel. By combining these two effects in a single stable polymer it supports a healthy barrier, improves moisture retention and leaves skin feeling velvety without the sting that can come from free acids.
It is still something of a niche ingredient, most often found in mid to high-end moisturizers and leave-on treatments rather than mass-market lines, yet formulators who work with it tend to keep using it because of its balanced performance.
Current safety reviews show it to be well tolerated for the vast majority of users with minimal risk of irritation or pore blockage. As with any new skincare addition it’s smart to patch test first to make sure your skin agrees with it.