What Is Polyester-18?
Polyester-18 is a man-made polymer created when four building blocks—fumaric acid, methylhexahydrophthalic acid, dimethyl propanediol and cyclohexane dimethanol—are linked together in a condensation reaction that releases water. The result is a flexible yet durable resin that spreads easily on skin, hair and nails.
The beauty industry began looking at this type of polyester in the late 1990s when labs searched for film formers that felt lighter than traditional oils and waxes. Its smooth feel and strong adhesive power soon made it a favorite for long-wear makeup and nail products. Production starts with the individual acids and alcohols, which are heated under carefully controlled conditions until they join into long chains. Once cooled and purified the solid resin is ground into a fine powder or melted into pellets, ready to blend into cosmetic formulas.
You are most likely to find Polyester-18 in nail polishes, top coats, mascara, liquid eyeliners, long-lasting foundations, hair styling creams, peel-off masks and some water-resistant sunscreens where a clear flexible film is needed.
Polyester-18’s Cosmetic Benefits/Uses
In formulas Polyester-18 plays several helpful roles that boost texture, wear time and overall performance.
- Binding: Helps hold pigments, shimmer or other particles together so the product looks even and stays put after application
- Film forming: Creates a thin flexible layer on skin, hair or nails that improves wear time, resists smudging and can add shine
- Nail conditioning: Gives nail polishes better grip and flexibility which reduces chipping while leaving nails feeling smoother
- Viscosity controlling: Adjusts thickness so creams, gels or polishes spread easily without running or feeling too heavy
Who Can Use Polyester-18
Because Polyester-18 is an inert synthetic resin it is generally well tolerated by all skin types, including oily, dry, sensitive and combination skin. It sits on the surface as a film former rather than soaking deep into the skin so it rarely triggers issues linked to barrier weakness or excess oil. People with very reactive or allergy-prone skin may still prefer to scan ingredient lists carefully but most users do fine with it.
The ingredient is produced entirely from laboratory-made raw materials so it contains no animal derivatives, making it suitable for vegans and vegetarians. As always cruelty-free status depends on the finished brand’s testing policies rather than the ingredient itself.
Polyester-18 is a large molecule that is not expected to pass through the skin into the bloodstream. For that reason it is considered low risk for people who are pregnant or breastfeeding. This is not medical advice and anyone who is expecting or nursing should run the full product lineup past a healthcare professional just to be safe.
The polymer does not increase sun sensitivity, so it will not make skin burn more easily. It can even boost the water-resistant hold of sunscreens applied on top of or underneath it. There are no known interactions with common actives like retinol, vitamin C or acids, so it fits well into most routines.
Potential Side Effects/Adverse Reactions
Responses to any cosmetic ingredient can differ from person to person. The points below outline potential side effects from topical use of Polyester-18, though most people will not experience them when the product is formulated and used properly.
- Mild skin irritation – a small number of users may notice redness, itching or warmth where the product sits
- Contact dermatitis – very rare allergy-type reaction that can cause rash or swelling in sensitive individuals
- Eye irritation – if a product like mascara or eyeliner containing Polyester-18 gets into the eyes it may cause stinging or watering until rinsed out
- Nail plate brittleness – heavy layers of long-wear polish or top coat that seal the nail for days can sometimes dry it out making it feel harder and more prone to splitting
If any discomfort, rash or other negative effect appears stop using the product and seek medical advice if symptoms persist
Comedogenic Rating
Rating: 1/5
Polyester-18 earns a low score because its large molecular size means it stays on the surface rather than sinking into pores. It forms a light flexible film instead of a thick greasy seal, so there is little risk of it trapping excess oil or dead skin. For most people prone to acne or breakouts this ingredient is considered safe, though very heavy layers in highly occlusive formulas could contribute to congestion if not removed properly at the end of the day.
Since it is often paired with pigments and waxes in long-wear makeup, the overall formula can matter more for clogging potential than Polyester-18 itself. Proper cleansing will help keep buildup from becoming an issue.
Summary
Polyester-18 is a lab made film former that binds pigments, conditions nails and fine tunes viscosity so products glide on smoothly and stay put. It does this by creating a clear flexible mesh across skin, hair or nails that holds everything in place while resisting water and smudging.
You will mostly see it in nail polish, mascara and long wear foundations rather than everyday moisturizers, so its popularity is solid within color cosmetics but limited in basic skincare.
Overall safety is high because the polymer is inert, non penetrating and rarely irritating. Still, skin can react unpredictably so it is wise to patch test any new product containing Polyester-18 before full use.