What Is Polyester-39?
Polyester-39 is a synthetic polymer created when dilinoleic acid, a fatty acid derived from plant oils, reacts with propanediol, a small alcohol molecule. The resulting long chain is then capped with octyldodecanol, a silky fatty alcohol, and PEG-6 sesqui(benzotriazolyl t-butyl hydroxyphenylpropionate), a stabilising agent that helps protect the polymer and any formula it sits in from light damage. Chemists began experimenting with this combination in the early 2000s while looking for a flexible thin film that could sit comfortably on skin. Its ability to spread evenly without feeling heavy quickly attracted the interest of formulators working on sunscreens and long-wear makeup, and within a decade Polyester-39 appeared in a wide range of products.
Manufacturing starts with purifying plant-sourced dilinoleic acid and fermenting feedstock to obtain propanediol. These two ingredients are heated together under controlled conditions until they form repeating polyester links. Once the desired chain length is reached, the reaction is stopped and the polymer ends are capped with octyldodecanol and the PEG-6 stabiliser. The finished material is a soft, waxy solid that is melted or dispersed into cosmetic bases.
You will most often see Polyester-39 in facial sunscreens, tinted moisturisers, long-lasting foundations, waterproof mascaras, peel-off masks and some anti-aging serums where a smooth, flexible film is needed to lock active ingredients in place or resist sweat and water.
Polyester-39’s Cosmetic Benefits/Uses
Polyester-39 brings a single but valuable action to a formula.
Film forming: Once applied it dries to a thin, invisible layer that helps active ingredients stay put, improves water and sweat resistance, reduces transfer of makeup onto clothes and keeps the skin surface feeling smooth. This film can also give a soft-focus finish that visually blurs fine lines and pores, boosting the overall sensory appeal of the product.
Who Can Use Polyester-39
Polyester-39 is considered compatible with most skin types including dry, normal, combination and oily skin because it forms a breathable, flexible film that is neither overly occlusive nor drying. Very acne-prone or highly sensitive skin may want to monitor how it performs since any film former can potentially trap excess oil or irritants, which might aggravate breakouts or redness in a small subset of users.
The raw materials come from plant oils and biobased propanediol, and no animal-derived substances are involved in its manufacture, so products using Polyester-39 are generally suitable for vegans and vegetarians. Always check the full ingredient list of the finished product in case other non-vegan ingredients are present.
Current safety data do not flag Polyester-39 as a reproductive or developmental hazard, so it is not automatically restricted for pregnant or breastfeeding women. That said, this is not medical advice and anyone who is pregnant or nursing should review all skincare products with a qualified healthcare provider for individual guidance.
The ingredient does not increase photosensitivity and actually helps stabilise UV filters, making it a common addition to sunscreens. It has no known interactions with common topical actives, though its film may slightly slow the penetration of leave-on treatments applied over it.
Potential Side Effects/Adverse Reactions
Reactions to the topical use of Polyester-39 differ from person to person. The effects listed below are only potential outcomes and are unlikely to occur for most people when the ingredient is formulated and used correctly.
- Mild skin irritation – tingling or redness, usually short lived, in individuals with very reactive skin
- Contact allergy – rare cases of sensitisation to the PEG end-group may cause itching or rash
- Acne flare-up – the occlusive film can occasionally trap sebum and debris on blemish-prone skin leading to clogged pores
- Eye stinging – if a product migrates into the eyes the film may cause temporary discomfort or watering
- Product buildup – daily use without proper cleansing might leave a residue that dulls skin’s appearance
If any adverse reaction occurs discontinue use and seek advice from a medical professional or licensed dermatologist.
Comedogenic Rating
Rating: 1/5
Polyester-39 is a large, non-penetrating polymer that sits on the surface of skin and creates a breathable film rather than sinking into pores. Its light occlusivity helps hold in moisture and protect formulas but is not heavy enough to consistently block follicles. A tiny subset of very oily or congested skin types may notice extra buildup if cleansing is inadequate, yet most users will not experience clogged pores.
Overall Polyester-39 is generally suitable for acne-prone or breakout-prone skin, provided the finished product is removed thoroughly at the end of the day.
Because it is almost always blended with other ingredients, the comedogenic potential of the full formula depends more on the oils, waxes and pigments surrounding Polyester-39 than on the polymer itself.
Summary
Polyester-39 is a film former that dries to a thin, flexible layer which locks active ingredients in place, boosts water and sweat resistance and gives makeup a smoother longer-wearing finish. It achieves this through its long polyester backbone and carefully chosen end-caps that stabilise the chain and help it spread evenly on skin.
While not as famous as silicones, Polyester-39 has carved out a steady following in modern sunscreens, foundation sticks, waterproof mascaras and peel-off masks thanks to its light feel and reliable performance.
Current safety data show a low risk of irritation or sensitisation and no systemic concerns, making it a broadly safe choice for everyday cosmetics. As with any new skincare ingredient it is wise to patch test a fresh product first to be sure your individual skin tolerates the formula.