What Is Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate?
Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate is a man-made polymer created from the reaction of isophthalic acid with the sugar alcohol pentaerythritol, then finished off, or “end-capped,” with either benzoic acid or isostearic acid. The result is a large, stable molecule that behaves like a flexible mesh when it dries on the skin or hair.
This ingredient was introduced in the early 2000s when formulators were looking for film formers that could give makeup longer wear without feeling heavy or sticky. By adjusting the type of acid used to cap the polymer, chemists could fine-tune how shiny, soft or water-resistant the final film would be, making it an attractive alternative to older resins that tended to crack or flake.
Production involves heating isophthalic acid with pentaerythritol in the presence of a catalyst so the two link together, releasing water. Once the desired chain length is reached, benzoic acid or isostearic acid is added to stop the reaction and provide extra softness and flexibility. The finished polymer is then purified, ground into a fine powder or dispersed in a carrier oil ready for cosmetic use.
You will most often find Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate in long-wear foundations, transfer-resistant lipsticks, waterproof mascara, eyeliners, sunscreens, primers, setting sprays, hair styling creams and some lightweight moisturizers that aim for a smooth, non-greasy finish.
Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate’s Cosmetic Benefits/Uses
This multifunctional polymer improves both how a formula feels and how it performs on the skin or hair.
- Film forming: Creates a thin, flexible layer that locks pigments in place, boosts water resistance and helps active ingredients stay on the skin longer which means makeup lasts through heat, sweat and humidity without cracking
- Viscosity controlling: Thickens liquids just enough to keep particles evenly suspended so the product glides on smoothly and does not separate during storage giving a consistent feel from the first application to the last
Who Can Use Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate
Because it is a large, inert synthetic polymer, Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate is generally well tolerated by all skin types, including sensitive, oily and dry. It does not penetrate deeply or disrupt the skin’s natural balance, so most people can use it without concern. Those with extremely oily or congestion-prone skin may prefer lighter layers, as any film former has the potential to trap excess sebum if applied too heavily.
This ingredient is produced entirely from petroleum- or plant-derived raw materials and contains no animal by-products, so formulations using it are suitable for both vegetarians and vegans.
Current safety data show no evidence that the polymer is absorbed into the bloodstream or interferes with hormones, meaning it is not known to pose a risk during pregnancy or breastfeeding. That said, this is not medical advice; anyone who is pregnant or nursing should review all skincare products with a qualified healthcare professional before use.
Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate does not make skin more sensitive to the sun. In fact, its film-forming ability can help water-resistant sunscreens stay in place longer. It is also considered eye-area safe at the levels typically used in mascaras and eyeliners.
Potential Side Effects/Adverse Reactions
Reactions to topical Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate vary from person to person. The points below describe potential side effects that could occur, though they are uncommon when the ingredient is used correctly in a finished product.
- Mild skin irritation: Rare stinging or redness, usually in individuals with highly reactive skin
- Contact dermatitis: Isolated reports of rash or itching, often linked to sensitivity to residual monomers or other formula components rather than the polymer itself
- Eye irritation: Temporary watering or discomfort if product containing the polymer accidentally gets into the eye before it has set
- Follicular clogging: Very heavy or repeated layers might trap sebum and debris, potentially contributing to breakouts in acne-prone users
- Build-up on hair: In styling products, continuous use without proper cleansing can leave a film that makes strands feel dull or coated
If any irritation, rash or other negative reaction is noticed, stop using the product and consult a healthcare professional for further guidance.
Comedogenic Rating
Rating: 1/5
This polymer sits on the surface, forms a breathable film and has molecules that are too large to slip into pores. Laboratory data show it does not feed acne-causing bacteria or block oil flow the way heavier waxes and oils can. That said, piling on multiple layers without proper cleansing may trap sebum and dead cells, which is why the score is not a perfect zero.
Overall it is suitable for people prone to acne or breakouts, especially when used in lightweight formulas and removed thoroughly at the end of the day.
Water-based or alcohol-based products containing this ingredient tend to be the least likely to leave residue, while very rich creams with added occlusives could raise the risk of congestion.
Summary
Isophthalic Acid/Pentaerythritol Crosspolymer Benzoate/Isostearate works mainly as a film former and mild thickener. It lays down a flexible mesh that locks pigments and actives in place making makeup and sunscreen last longer through sweat and humidity. At the same time it fine-tunes viscosity so products feel smooth and stay mixed from bottle to skin.
It is not the most famous cosmetic polymer but you will spot it more and more in long-wear foundations, waterproof mascaras and light creams because it offers hold without a heavy feel.
Current research rates it as very safe with low risk of irritation or pore blockage. Still, everyone’s skin is unique so it is smart to patch test any new product that lists this ingredient before putting it into daily rotation.