What Is Pei-15?
Pei-15 is the cosmetic name for a synthetic ingredient known in chemistry circles as aziridine homopolymer. It is created in a lab by linking together many small aziridine molecules in a controlled reaction that forms a smooth flowing polymer. Unlike naturally sourced gums or clays, Pei-15 is entirely man-made which allows tight control over its purity, thickness and performance from batch to batch.
The material first found use in industrial coatings where steady, predictable flow is essential. Formulators soon saw the same benefits for personal care, so Pei-15 began showing up in skin and hair products during the late 1990s. Today it is produced in closed reactors where temperature, pressure and pH are carefully managed. After polymerization the mixture is filtered and neutralized, then blended into an easy-to-handle liquid or powder that ships to cosmetic labs around the world.
You will most often notice Pei-15 in products that need to feel rich yet spread evenly on the skin, such as moisturizing creams, eye gels, overnight masks, styling gels, sunscreens and some liquid foundations. A small amount can transform a watery formula into a velvety lotion without adding greasiness.
Pei-15’s Cosmetic Benefits/Uses
Pei-15 is prized for one key job in formulations.
As a viscosity controlling ingredient it adjusts how thick or thin a product feels. By tuning flow, Pei-15 helps prevent watery products from running off the skin while keeping heavier creams from feeling sticky. The result is a smoother application, better suspension of pigments or actives and an overall more elegant texture.
Who Can Use Pei-15
Pei-15 is considered friendly for most skin types including oily, dry, combination and sensitive because it is an inert polymer that simply fine-tunes texture rather than delivering an active chemical punch. People with extremely reactive skin or a known sensitivity to amine-based polymers may want to proceed cautiously, as they could be more prone to redness or stinging.
The ingredient is synthesized in a lab from petrochemical feedstocks and contains no animal-derived materials, so it is suitable for vegans and vegetarians. Manufacturers who follow cruelty-free standards can also use Pei-15 without compromising those claims.
Current safety data show no specific concerns for pregnant or breastfeeding women when Pei-15 is used topically at the levels found in finished cosmetics. This is not medical advice, and anyone who is pregnant or nursing should run any skincare routine past their doctor to be on the safe side.
Pei-15 does not absorb UV light or interact with sunlight, so it is not known to cause photosensitivity. It also plays well with common actives like niacinamide, retinol and vitamin C because it does not change pH or oxidation state.
Potential Side Effects/Adverse Reactions
Reactions to topical Pei-15 can vary from person to person. The points below outline potential side effects that might occur, but they are uncommon when the ingredient is used correctly in a well-formulated product.
- Mild skin irritation such as transient redness or itching, more likely on compromised or freshly exfoliated skin
- Allergic contact dermatitis in individuals who have a specific sensitivity to polyaziridine compounds
- Eye irritation if the product accidentally gets into the eyes while still wet
- Drying sensation if used at high concentrations in leave-on products, as the polymer can bind water away from the skin surface
If any of the above reactions occur stop using the product and consult a healthcare professional for further guidance.
Comedogenic Rating
Rating: 0 / 5. Pei-15 is a large, water-soluble polymer that sits on the surface then rinses away without melting into sebum or plugging follicles. It lacks the oily backbone and film-forming nature seen in ingredients that typically trigger breakouts, so the chance of it clogging pores is very low.
Because of this, Pei-15 is generally considered suitable for acne-prone or breakout-prone skin types.
One extra note: in very thick formulations the overall product, not Pei-15 itself, could feel heavier which might bother some users who prefer ultra-light textures, but the polymer alone does not add comedogenic risk.
Summary
Pei-15 is a lab-made aziridine homopolymer used mainly to control viscosity, turning runny mixtures into silky lotions or keeping gels from sliding off the skin. By tweaking flow it helps suspend pigments and actives, improves spreadability and delivers a more luxurious feel without greasiness.
It is a niche yet handy tool for formulators, popping up most often in moisturizers, sunscreens and styling gels rather than in every product on the shelf. Those who do use it appreciate its reliability and ease of processing.
Current data suggest Pei-15 is low risk for irritation, non-comedogenic and free of major safety flags when applied topically at cosmetic levels. As with any new skincare ingredient, do a quick patch test when trying a product containing Pei-15 to confirm personal compatibility.