What Is Glycerin/Phthalic Acid Copolymer Hydroxypropyl C9-11 Isoalkyl Acidate?
Glycerin/Phthalic Acid Copolymer Hydroxypropyl C9-11 Isoalkyl Acidate is a lab made ingredient created by linking plant derived glycerin molecules with phthalic acid units, then attaching long branched chains called C9-11 isoalkyl groups through an epoxy driven reaction. The result is a flexible, oil like polymer that behaves as a lightweight skin conditioner.
Glycerin has been used in skincare for well over a century, but researchers wanted an option that kept its moisture friendly feel while adding a smoother, silkier finish. Polymer chemists discovered that combining glycerin with phthalic acid produced a backbone that could be further modified to give extra slip and cushion. By the early 2000s this copolymer began appearing in premium moisturizers and color cosmetics, offering a modern alternative to heavier mineral oils.
Manufacturing starts with food grade glycerin and purified phthalic anhydride. These two react under heat to form an initial polyester chain. An epoxy compound bearing hydroxypropyl C9-11 isoalkyl groups is then added, opening its ring and grafting feather-light side chains onto the backbone. The finished material is purified, cooled and supplied as a clear to pale yellow liquid that blends easily with oils and silicones.
You will see this copolymer in face and body lotions, hand creams, lipsticks, makeup primers, sheet masks, leave-on hair conditioners and many anti aging serums where formulators want a soft touch without a greasy afterfeel.
Glycerin/Phthalic Acid Copolymer Hydroxypropyl C9-11 Isoalkyl Acidate’s Cosmetic Benefits/Uses
This ingredient serves one main purpose in cosmetics, acting as an emollient that delivers several noticeable perks for skin feel and formula performance.
As an emollient it fills in tiny gaps on the skin surface, leaving it feeling smoother and more supple while helping to reduce moisture loss. The copolymer’s branching side chains spread easily so lotions glide on effortlessly and absorb quickly. It also adds a subtle protective film that makes makeup last longer and keeps creams from feeling sticky.
Who Can Use Glycerin/Phthalic Acid Copolymer Hydroxypropyl C9-11 Isoalkyl Acidate
This emollient is light enough for oily or combination skin yet cushioning enough for normal and dry skin, making it broadly suitable for most skin types. Because it is non reactive and free of known irritants it is also considered gentle for sensitive skin. People dealing with very severe or cystic acne may wish to monitor how their skin responds since any emollient has a small chance of feeling too rich for them.
The starting materials are plant based glycerin and synthetic acids produced without animal by products so the ingredient is appropriate for both vegetarians and vegans.
No data suggest reproductive or developmental risks with topical use. The polymer is large, remains on the surface and is not known to penetrate deeply. That said this is not medical advice and anyone who is pregnant or breastfeeding should review any skin care product with a qualified health professional before use just to be safe.
The copolymer is not photo reactive and will not make skin more sensitive to sunlight. It can be worn day or night and pairs well with sunscreens, antioxidants and other active ingredients without stability issues.
Potential Side Effects/Adverse Reactions
Responses to topical ingredients vary from person to person. The following is a list of potential side effects associated with Glycerin/Phthalic Acid Copolymer Hydroxypropyl C9-11 Isoalkyl Acidate. These outcomes are uncommon when the finished product has been properly formulated and most users will not notice any problems.
- Mild redness or irritation in individuals with extremely sensitive skin
- Transient stinging if applied to freshly exfoliated or broken skin
- Rare allergic contact dermatitis marked by itching or small bumps
- Potential for pore clogging in skin that is very acne prone when used in heavy leave on products
If you experience any discomfort stop using the product and consult a healthcare professional.
Comedogenic Rating
Rating: 1 / 5
This copolymer is a large, branched molecule that tends to sit on the surface rather than seep into pores, so it is far less likely to trap oil or debris compared with heavier plant butters or straight-chain oils. Formulators usually include it at low to moderate levels, further reducing any clogging risk. For these reasons its score sits at 1 instead of 0, acknowledging that very acne prone skin can still react to almost any emollient if the overall formula is overly rich.
Suitable for most people who are prone to acne or breakouts, especially when used in lightweight lotions or serums.
If it appears high on an ingredient list alongside occlusive waxes or oils, the chance of congestion can rise so context matters.
Summary
Glycerin/Phthalic Acid Copolymer Hydroxypropyl C9-11 Isoalkyl Acidate acts primarily as a modern emollient. Its glycerin–phthalic backbone binds water lightly while the isoalkyl side chains glide over skin, filling in rough spots and leaving a silky afterfeel without a greasy residue. This dual action helps formulas spread easily, lock in softness and improve makeup wear.
While not as famous as classic ingredients like dimethicone or shea butter, it is gaining quiet traction in mid to high end moisturizers, primers and lip products that aim for a feather light finish.
Current safety data show it is well tolerated, non sensitizing and non photoreactive. As with any new skincare ingredient it is wise to patch test a small area first to be on the safe side.