What Is Pei-35?
Pei-35 is the cosmetic name for a synthetic polymer made by linking together many molecules of aziridine, a three-membered nitrogen ring. When the rings open and connect they form a branched chain called polyethylenimine, which chemists label by its average molecular weight, in this case about 35 000 daltons. Because it is produced in a lab from petrochemical feedstocks it is considered a fully man-made ingredient rather than a plant or animal derivative.
The polymer first appeared in industrial applications in the 1950s where it was prized for its ability to thicken water-based solutions. Formulators in personal care soon noticed that the same property could help stabilize creams, gels, and hair products so by the late 1970s Pei-35 had started to appear in commercial cosmetic lines.
Manufacturing begins with purified aziridine, which is treated under controlled heat and pressure with an acid catalyst. The strained ring opens, units link together, and the reaction stops once the desired chain length is reached. The resulting polymer is then neutralized, filtered, and standardized into either a concentrated solution or a solid powder.
Today Pei-35 shows up in a variety of topical products. Skincare brands use it in moisturizers, anti-aging serums, sheet mask essences, and peel-off masks where a smooth, cushiony texture is important. Haircare producers add it to conditioners, styling creams, and gels for better spreadability and hold. It can also pop up in liquid foundations, primers, and other color cosmetics that need consistent flow.
Pei-35’s Cosmetic Benefits/Uses
Pei-35 serves a single yet valuable purpose in formulas.
Viscosity controlling: the polymer thickens watery mixtures and helps suspend pigments, oils, or actives so the product feels even and luxurious when applied. This control over flow prevents ingredients from separating in the bottle, keeps creams from running off the skin, and lets formulators fine-tune texture without adding heavy fats or waxes.
Who Can Use Pei-35
Pei-35 is generally considered compatible with all skin types including oily, combination, normal and dry because it functions only as a texture helper rather than an active that alters skin biology. People with highly sensitive or easily irritated skin can usually tolerate it as well, although they may want to pay attention to any other ingredients paired with it since those, not Pei-35, are more likely to trigger reactions.
The polymer is completely synthetic and contains no animal derived components so it is suitable for both vegetarians and vegans. No animal testing is required to produce Pei-35 itself though finished products may follow local regulatory requirements.
Current safety data show no specific risks for pregnant or breastfeeding women when Pei-35 is used topically at the low levels typical in cosmetics. This is not medical advice and anyone who is pregnant or nursing should still review all personal care products with a healthcare professional to be safe.
Pei-35 does not absorb ultraviolet light and therefore does not cause photosensitivity. It also has no known interactions with common skincare actives like retinoids or acids because it acts only on the formula’s viscosity.
Potential Side Effects/Adverse Reactions
Reactions to topical Pei-35 vary from person to person. The points below represent potential though uncommon side effects when the ingredient is included at standard cosmetic concentrations. Most users will not experience any of these issues if the product has been manufactured correctly.
- Mild skin redness or warmth
- Transient stinging on very compromised or freshly exfoliated skin
- Contact dermatitis in individuals already sensitized to polyamine compounds
- Eye irritation if a product containing Pei-35 accidentally gets into the eyes
If you notice any of these effects discontinue use and consult a healthcare professional or dermatologist for guidance.
Comedogenic Rating
Rating: 0/5 (non-comedogenic)
Pei-35 is a large water-soluble polymer that remains on the surface of the skin and contains no oils, fats or waxes that could clog pores. It is typically used at well under 1 percent, further limiting any chance of buildup inside follicles.
This profile makes Pei-35 suitable for people prone to acne or frequent breakouts.
No evidence links the polymer to fungal acne or excess sebum production. If irritation does occur, it is usually tied to other ingredients in the finished product rather than Pei-35 itself.
Summary
Pei-35 is a synthetic polyethylenimine that keeps lotions, gels and hair products at the right thickness by forming a flexible network in water. This network suspends pigments, actives and oils so the formula stays uniform and glides on smoothly.
While not a star ingredient called out on labels, it is a quiet favorite among formulators thanks to its dependable performance at tiny concentrations.
Available safety studies and decades of cosmetic use point to a very low risk profile, though it is always smart to patch test any new product to be sure your skin tolerates the complete formula.