What Is Pei-275?
Pei-275 is the cosmetic name for a synthetic ingredient made from aziridine that is reacted with itself to create a homopolymer. The process, called ring-opening polymerization, strings many aziridine units together into a smooth clear polymer that mixes well with water and many oils. First developed for industrial coatings where it added thickness without clouding, formulators soon noticed its stability and tidy texture. By the early 2000s it began appearing in personal-care research as a gentler alternative to older thickeners that could feel sticky or heavy. Today Pei-275 is manufactured in closed reactors to keep the reactive aziridine monomer contained until it is fully polymerized and neutralized, leaving behind a high-molecular-weight material that is no longer reactive. You will most often see it in lightweight facial creams, sheet mask essences, anti-aging serums, hair gels, sunscreens and specialty treatments that need a silky yet controlled flow.
Pei-275’s Cosmetic Benefits/Uses
Pei-275 serves a single but important role in formulas.
As a viscosity-controlling agent it helps a product achieve the ideal thickness so it spreads evenly, stays where you put it and feels elegant on the skin or hair. Because it works at low use levels it lets formulators keep the finished product light while still preventing separation of water and oil phases, improving stability and shelf life.
Who Can Use Pei-275
Pei-275 is considered friendly to most skin types including oily, combination, normal and dry because it is an inert polymer that does not add oil or draw out moisture. Extremely sensitive or highly reactive skin may still prefer to avoid unnecessary synthetics, yet reports of irritation are rare.
The ingredient is made entirely through chemical synthesis with no animal-derived feedstocks so it is suitable for both vegans and vegetarians.
Current data show no hormonal activity or systemic absorption, so products containing Pei-275 are generally viewed as safe during pregnancy or while breastfeeding. This is not medical advice and anyone who is pregnant or nursing should review their skincare routine with a healthcare professional before use to be safe.
Pei-275 is not known to increase photosensitivity, and it plays well with common actives like vitamin C, niacinamide and sunscreens because it simply thickens rather than reacting with them.
Potential Side Effects/Adverse Reactions
Side effects and reactions to the topical application of Pei-275 can vary from person to person. The following points outline potential issues, though most users experience none of them when the ingredient is properly formulated.
- Mild transient stinging on very compromised or freshly exfoliated skin
- Redness or itching linked to rare individual sensitivity
- Contact dermatitis if combined with other irritants in a poorly balanced formula
- Eye irritation if the product accidentally gets into the eyes before it sets
If any of these reactions occur stop use and consult a qualified medical professional.
Comedogenic Rating
Rating: 0 / 5
Pei-275 is a large water-compatible polymer that sits on the skin surface and contains no oils or waxes, so it does not settle into pores or create an occlusive film that could trap sebum. Because it stays mostly in the upper layers and is removed easily with regular cleansing it earns the lowest possible comedogenic score.
That means it is generally suitable for people who are prone to acne or breakouts. As always the overall formula matters, so if Pei-275 is blended with richer plant butters or silicones the finished product could still feel heavy on very oily skin.
Summary
Pei-275 is a lab-made homopolymer of aziridine used almost exclusively to control viscosity in skincare, haircare and sun care. Its high molecular weight chains tangle with water and oil droplets to create a smooth uniform flow that keeps creams stable, stops serums from dripping and gives gels a pleasant cushiony feel without greasiness.
The ingredient is still relatively niche compared with classic thickeners like carbomer or xanthan gum but formulators who need a clear lightweight texture are turning to it more often thanks to its versatility and low use level.
Current safety data show minimal risk: it is non-comedogenic, non-sensitizing for most people and not absorbed into the bloodstream. Even so every skin is unique so patch testing any new product that contains Pei-275 is a smart precaution.