Ingredient review
C9-11 Pareth-40
INCI: C9-11 PARETH-40
A synthetic cleansing agent that helps remove dirt and oil, but may be drying for sensitive skin.
In plain English
C9-11 Pareth-40 is a man-made ingredient that helps water mix with oil and dirt so they can be rinsed away. It's a type of surfactant, which is the foaming or cleansing part of many face washes and shampoos. The '40' means it has a long chain of ethylene oxide units, making it milder than some shorter-chain surfactants, but it can still strip natural oils if used too often.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Main practical flags: irritation is moderate; clogging risk is low.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- moderate
- Clogging risk
- low
Quick decision guide
Useful, but context matters
C9-11 Pareth-40 can be useful, but watch for some irritation potential.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging C9-11 Pareth-40.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
moderateCan bother some users, especially with frequent use, damaged skin, or strong companion ingredients.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
A synthetic ethoxylated alcohol surfactant derived from a blend of C9-C11 fatty alcohols and ethylene oxide.
How it works
It reduces the surface tension between water and oil, allowing oily dirt and sebum to be lifted from the skin and washed away. In emulsions, it helps keep oil and water droplets mixed together for a stable cream or lotion.
Pros
Effective cleanser
Removes excess oil, makeup, and daily grime without leaving a heavy residue.
Good emulsifier
Helps create stable, smooth creams and lotions that don't separate.
Cons and cautions
Potential for dryness
Can strip natural oils, leading to tightness or irritation, especially in leave-on products.
Ethoxylation concerns
Manufacturing may produce trace amounts of 1,4-dioxane, a potential contaminant; reputable brands purify to low levels.
Best for
- People with normal to oily skin looking for a thorough cleanse
- Those who use rinse-off products like face washes and shampoos
Use caution if
- Individuals with very dry, compromised, or eczema-prone skin
- Anyone seeking a completely natural or non-ethoxylated ingredient
Usage tips
Safety summary
Generally considered safe for rinse-off use at typical concentrations. The main concern is potential skin dryness and trace 1,4-dioxane, which is regulated. Patch test if you have sensitive skin.
Research notes
Studies show ethoxylated alcohols are effective surfactants with moderate irritation potential. The Cosmetic Ingredient Review (CIR) panel has reviewed similar ethoxylates and found them safe when formulated to minimize impurities.
Common label clues
- Typical concentration
- 0.5% to 5% in rinse-off products; lower in leave-on formulas
- Regulatory status
- Approved for use in cosmetics in the US, EU, and many other regions. Manufacturers are expected to keep 1,4-dioxane levels low (typically under 10 ppm).
- Common uses
- Cleansers, Shampoos, Body washes, Emulsions
- Environmental note
- Synthetic and petroleum-derived; not readily biodegradable in all conditions, though some ethoxylates break down over time.
Good to know
- The '40' refers to the number of ethylene oxide units, which generally makes it milder than shorter-chain versions.
- Often found in sulfate-free cleansers as a gentler alternative to sodium lauryl sulfate.
Common questions
What is C9-11 Pareth-40 in beauty products?
C9-11 Pareth-40 is a man-made ingredient that helps water mix with oil and dirt so they can be rinsed away. It's a type of surfactant, which is the foaming or cleansing part of many face washes and shampoos. The '40' means it has a long chain of ethylene oxide units, making it milder than some shorter-chain surfactants, but it can still strip natural oils if used too often.
What does C9-11 Pareth-40 do in a beauty product?
It reduces the surface tension between water and oil, allowing oily dirt and sebum to be lifted from the skin and washed away. In emulsions, it helps keep oil and water droplets mixed together for a stable cream or lotion.
Is C9-11 Pareth-40 safe for most people?
Generally considered safe for rinse-off use at typical concentrations. The main concern is potential skin dryness and trace 1,4-dioxane, which is regulated. Patch test if you have sensitive skin.
Who should be careful with C9-11 Pareth-40?
Individuals with very dry, compromised, or eczema-prone skin Anyone seeking a completely natural or non-ethoxylated ingredient
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.