PEI-35

Also known as: Polyethyleneimine (MW ~1,500)

INCI: PEI-35 | Function: Film Former, Conditioning Agent | Type: Cationic Polymer (Polyethyleneimine)

What Is PEI-35?

PEI-35 is a polyethyleneimine (PEI) with an average molecular weight of approximately 1,500 Daltons. PEIs are cationic (positively charged) polymers synthesized from aziridine monomers. They function as film formers, conditioning agents, and fixatives in cosmetic formulations, adhering strongly to negatively charged surfaces like skin and hair. Lower MW variants (PEI-7 to PEI-45) are used in skincare for light film-forming; higher MW variants (PEI-250+) are primarily used in hair styling products for strong hold.

Key Skin Benefits

+ Forms protective film — reduces TEWL and locks in moisture
+ Hair conditioning — cationic nature adheres to damaged hair cuticles
+ Styling hold — higher MW grades provide flexible or firm hold
+ Anti-static — neutralizes flyaway hair

Pros

+ Effective at low concentrations (0.1-2%)
+ Cationic charge provides substantivity to skin and hair
+ Water-soluble — easy to formulate
+ Combines well with anionic surfactants in rinse-off products

Cons

− High MW variants may cause build-up on hair
− Potential eye irritant at high concentrations
− Synthetic origin — not suitable for natural formulations
− Limited safety data for very high MW grades (>1,000 Da) in leave-on

Specifications

Property	Value
Usage Areas	Face, Body, Hair
Product Type	Leave-On, Rinse-Off
Source	Synthetic
Natural Level	Synthetic

Safety Ratings

Metric	Rating
Skin Sensitivity	2/5
Comedogenic Rating	0/5
EWG Score	3/10

Regional Regulatory Limits

Region	Leave-on %	Rinse-off %	Status
EU (CosIng)	No limit	No limit	Allowed
US (CIR/FDA)	No limit	No limit	Allowed
Japan (MHLW)	No limit	No limit	Allowed
ASEAN	No limit	No limit	Allowed
China (NMPA)	No limit	No limit	Allowed

Typical Usage % by Product Type

Product Type	Typical %
Hair styling gel	0.5 - 3%
Leave-on serum	0.1 - 0.5%
Shampoo / Conditioner	0.2 - 1%

References

CIR (2020) — Safety Assessment of Alkyl Polyethyleneimines as Used in Cosmetics. cir-safety.org
CosIng (2025) — European Commission Database. https://ec.europa.eu/growth/tools-databases/cosing/
SpecialChem — Polyethyleneimine cosmetic ingredient guide. https://cosmetics.specialchem.com/
EWG Skin Deep — PEI compounds database. https://www.ewg.org/skindeep/

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