What Is Polyester-4?
Polyester-4 is a man-made ingredient created by linking adipic acid with pentaerythritol, then capping the chain with lightweight fatty acids like caproic, heptanoic, caprylic and capric acid. The result is a smooth copolymer that behaves a lot like a flexible net on the skin. Chemists first explored this type of polymer in the late twentieth century while looking for gentle film formers that could stand up to water and sweat without feeling sticky. Today it is made in closed reactors where the raw acids and alcohols are heated so they join together and release water, a process called condensation. After purification the molten resin is cooled and ground into a fine powder that blends easily into cosmetic bases. You will most often find Polyester-4 in long-wear makeup, sunscreens, tinted moisturizers, peel-off masks, hair styling creams and transfer-resistant lip or brow products.
Polyester-4’s Cosmetic Benefits/Uses
Here is how this multitasking polymer helps improve everyday beauty formulas:
- Film forming: Creates an invisible flexible layer that locks pigments in place, boosts water resistance and helps active ingredients stay on the skin or hair longer
- Skin conditioning: Adds a soft silky feel that reduces tackiness, making creams spread more evenly and leaving skin feeling smooth rather than greasy
Who Can Use Polyester-4
Polyester-4 is considered friendly to all major skin types, including dry, normal and combination skin. Its lightweight breathable film makes it reasonably comfortable even for oily skin, though people who are extremely oil prone may prefer to use it in rinse-off or low-percentage leave-on formulas to avoid a heavy feel.
The ingredient is fully synthetic and contains no animal-derived matter so it is suitable for both vegans and vegetarians.
No data suggest that Polyester-4 poses any unique risk to women who are pregnant or breastfeeding. Because every pregnancy is different this information is not medical advice and anyone expecting or nursing should check any new skincare product with a qualified healthcare provider.
Polyester-4 is not known to make skin more sensitive to sunlight, so it does not increase the risk of sunburn.
Potential Side Effects/Adverse Reactions
Individual reactions to topical Polyester-4 can vary. The points below outline potential side effects that could occur even though most users will not experience them when the ingredient is used as intended by the manufacturer.
- Mild skin irritation: rare redness or stinging, usually in very sensitive skin
- Contact allergy: uncommon rash or itching if someone develops sensitivity to the polymer or residual monomers
- Clogged pores: possible bump formation in people who are highly acne prone if the product is very occlusive or layered thickly
- Build-up on hair: a dull coating can appear when used in hair products without periodic clarifying shampoo
If any irritation or other negative effect occurs stop using the product and seek professional advice if symptoms persist.
Comedogenic Rating
Rating: 1/5
Polyester-4 forms a thin breathable film that allows water vapor to pass through, so it is far less likely to block pores than heavier waxes or butters. Its fatty acid end groups are short chain and lightweight which further lowers the chance of pore congestion. Because it is nearly insoluble in skin sebum and used at modest levels in most formulas it earns a low score of one.
Overall Polyester-4 is generally suitable for acne-prone or breakout-prone skin, provided the rest of the product is also low in pore-clogging ingredients.
As with many film formers the final comedogenicity depends on the full formula and how thickly it is applied. Very occlusive products or heavy layering can raise the risk even when the raw polymer itself is mild.
Summary
Polyester-4 works chiefly as a film former and skin conditioner. By arranging itself into a flexible lattice on the surface it locks colorants, actives and moisture in place while leaving a smooth lightweight feel. This same structure adds slip to creams and lotions reducing tackiness.
The ingredient is moderately common in long-wear makeup, transfer-resistant lip colors, water-resistant sunscreens and certain hair styling products but it is not yet as widespread as silicones or acrylate copolymers. Formulators pick it when they need durability without a heavy or sticky finish.
Safety data indicate a low risk of irritation or sensitization when used at typical cosmetic levels. Even so every skin type is unique so it is smart to perform a small patch test when trying any new product that contains Polyester-4.