What Is Pei-2500?
Pei-2500 is the cosmetic trade name for a homopolymer of aziridine, a small ring-shaped molecule. When many aziridine units link together they form polyethylenimine, better known in formulas as Pei-2500. This synthetic ingredient is produced through controlled polymerization in a factory setting, which allows chemists to fine-tune the chain length and performance. Pei-2500 first entered the beauty scene in the late 1990s when formulators were searching for lighter alternatives to traditional thickeners. Because it can adjust the flow of a product without adding heaviness, it quickly found a place in masks, serums, water-based gels, sunscreens and leave-on treatments.
Pei-2500’s Cosmetic Benefits/Uses
Pei-2500 acts as a viscosity controlling agent, meaning it helps set how thick or runny a formula feels. By balancing viscosity it keeps a product from separating, makes it glide smoothly over the skin and ensures actives are evenly distributed with each use.
Who Can Use Pei-2500
Pei-2500 is generally compatible with most skin types including dry, oily and combination skin because it sits on the surface and controls texture rather than penetrating deeply. Sensitive skin can usually tolerate it as the polymer is inert, though anyone with a known sensitivity to polyethylenimines should steer clear.
The ingredient is produced synthetically with no animal-derived substrates so it is suitable for vegans and vegetarians.
Current research has not shown Pei-2500 to pose specific risks for pregnant or breastfeeding women when applied topically. That said this is not medical advice and those who are expecting or nursing should confirm any skincare routine with their physician to stay on the safe side.
Pei-2500 does not increase photosensitivity and it is stable in sunlight, meaning normal daytime use does not require extra sun protection beyond your usual SPF.
Potential Side Effects/Adverse Reactions
Side effects and reactions to topical Pei-2500 can vary from person to person. The points below list potential effects, but they are uncommon when the ingredient is correctly formulated and applied.
- Mild skin redness or warmth
- Temporary itching
- Stinging sensation when applied to broken or compromised skin
- Eye irritation if the product accidentally gets into the eyes
If any irritation or discomfort occurs stop use immediately and consult a medical professional if symptoms persist.
Comedogenic Rating
Rating: 0–1
The large, water-soluble chains of Pei-2500 stay on the surface of the skin and rinse away without seeping into pores. It contributes no oils or waxes that might block follicles, so the chance of breakouts is minimal.
This makes Pei-2500 generally suitable for people who are prone to acne or congestion.
If the finished product also contains rich butters or heavy silicones, overall pore-clogging potential can rise, so always consider the full formula.
Summary
Pei-2500 is a synthetic polyethylenimine that works as a viscosity controller, keeping lotions, gels and serums the right thickness so they glide smoothly and stay evenly mixed. It pulls this off by untangling or tightening its polymer chains in water, giving chemists precise control over texture.
You will spot it in a range of products from sheet mask essences to lightweight sunscreens, yet it rarely gets marketing spotlight, making it a quietly reliable favorite among formulators rather than a buzzword for shoppers.
Studies and real-world use point to a low risk of irritation or clogged pores, so most users can apply it with confidence. Still, skin is individual, so patch test any new product containing Pei-2500 to be sure it plays nicely with your complexion.