What Is Pei-10?
Pei-10 is the cosmetic name for a homopolymer of aziridine, a small ring-shaped molecule made from ethylene. When many aziridine units link together they form polyethyleneimine, commonly shortened to PEI, and Pei-10 refers to a specific molecular size within this family. First studied in the 1950s for industrial uses, its thickening ability soon drew interest from beauty formulators looking for gentler ways to improve product texture. Today it is produced in controlled reactors where purified ethylene is converted to aziridine then polymerized. After neutralization and filtration the finished polymer is supplied as a clear liquid or fine powder ready for cosmetic blending. You will most often find Pei-10 in serums, gel creams, sheet-mask essences, hair styling gels and rinse-off masks where a smooth, silky feel is desired without adding heavy oils or waxes.
Pei-10’s Cosmetic Benefits/Uses
Pei-10 is prized for one main job in skincare and haircare products
Viscosity controlling: By swelling slightly in water and forming a network between other ingredients, Pei-10 fine-tunes thickness so a formula is neither runny nor overly stiff. This helps lotions glide evenly, keeps serums from dripping through fingers and lets styling gels hold hair in place while still feeling light.
Who Can Use Pei-10Because Pei-10 works mainly as a texture adjuster and does not penetrate deeply, it is generally suitable for dry, oily, combination and normal skin. Even sensitive skin tends to tolerate it since the polymer sits on the surface rather than reacting inside the skin, though people with a history of amine sensitivities may want to be cautious.
Pei-10 is a fully synthetic material created from petrochemical feedstocks so it contains no animal ingredients. This makes it appropriate for vegans and vegetarians provided the finished product has also been certified cruelty free by the brand.
Pregnant or breastfeeding users are not expected to absorb meaningful amounts of Pei-10 through intact skin. Still, this is not medical advice and anyone who is expecting or nursing should check with a doctor before adding new products to their routine.
The ingredient does not increase photosensitivity, meaning it will not make skin more prone to sunburn. It is also fragrance free and carries very little charge at the pH of most cosmetics so it rarely interferes with other actives in a formula.
Potential Side Effects/Adverse Reactions
Responses to any cosmetic ingredient can differ from person to person. The points below list potential side effects of topical Pei-10 but most users will not experience them when the product is properly formulated.
- Mild skin irritation: fleeting itching or warmth can occur, usually in people with very reactive skin
- Redness or stinging: short lived redness may appear if the product is applied to freshly exfoliated or broken skin
- Contact dermatitis: rare allergic rash has been reported in individuals sensitive to amine containing compounds
- Eye irritation: accidental eye contact can cause tearing or discomfort until rinsed out
If any of these effects develop stop using the product and seek advice from a healthcare professional.
Comedogenic Rating
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Pei-10 is a water-soluble polymer that stays on the surface of skin, does not leave an oily film and rinses away easily, so it is considered non-comedogenic. This makes it a safe choice for people who are prone to acne or breakouts. Because it functions strictly as a texture enhancer and carries no lipids that could clog pores, it is unlikely to contribute to blackheads or whiteheads. The only time buildup could occur is if a formula is overloaded with heavy oils alongside Pei-10, in which case those other ingredients would be the primary concern.
Summary
Pei-10 is a polyethyleneimine polymer used in cosmetics to control viscosity, giving serums, gels and creams a smooth flow without making them greasy. It works by swelling slightly in water and creating a subtle network that thickens the formula just enough for easy, even application.
The ingredient is not a social media darling yet but formulators appreciate its reliability, so you will often find it tucked into newer lightweight textures. Safety studies and long years of industrial use show a low risk profile, with irritation or allergy remaining rare events. As with any new product it is wise to perform a quick patch test to confirm personal compatibility.