Undeceth-40
AKA “Undecyl Polyethylene Glycol Ether, PEG Undeceth”
Surfactant
Ingredient Facts
Undeceth-40
AKA: Undecyl Polyethylene Glycol Ether, PEG Undeceth
Surfactant · Cleansing · EWG: 4
Synthetic
Cleanser
Emulsifier
Skin Conditioner
Not Clean
Undeceth-40 is a cosmetic ingredient used as emulsion stabilising, skin conditioning, surfactant - cleansing. Assessed as safe by the CIR.
Effective at 1.6%
CAS #
127036-24-2
See origin →
Functions
Emulsion Stabilising
Forces oil and water to stay mixed instead of separating into layers. The unsung hero holding your lotion together.
Skin Conditioning
A catch-all term for ingredients that improve how skin looks and feels — softer, smoother, more supple. The workhorse behind most moisturizers.
Cleansing
Makes oil and water mix so dirt, makeup, and sunscreen can actually be washed away. The reason your face wash foams.
Locks in moisture
Traditional Use
A polyethoxylated surfactant synthesized in the 20th century as part of the development of modern cosmetic emulsifiers. It has no traditional use history and was created to solve formulation stability challenges.
Skin Types
●all-skin-types
Best For
General
Pregnancy & Breastfeeding Safe
Yes
EWG
4
CIR
Safe as used
Pregnancy
Yes
CIR Safety Findings
Not a Sensitizer
medical-approval
all-shades-safe
Concentration Guide
0.2%
3.0%
0%4%
Effective Range
CIR reported use: 0.7-2 | 1-3 | 0.2-3
Regulatory Agencies
Verified Jun 2026
Data: CosIng · EWG · CIR