Ingredient review
Undeceth-9
INCI: UNDECETH-9
Undeceth-9 is a workhorse emulsifier that helps products feel smooth and spread evenly, but it can be slightly drying or irritating for sensitive skin.
In plain English
Undeceth-9 is a synthetic ingredient that helps oil and water mix together in your skincare products. Think of it as a tiny bridge that keeps the formula from separating. It's often found in cleansers and shampoos to help them lather and rinse cleanly. While it's generally safe, it can strip natural oils if used too often, especially for dry or sensitive skin types.
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
Undeceth-9 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 Undeceth-9.
- 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
Undeceth-9 is a polyethylene glycol (PEG) ether of undecanol, a fatty alcohol. It belongs to a class of surfactants that reduce surface tension, allowing water and oil to blend. It is produced synthetically and is commonly used as an emulsifier and cleansing agent.
How it works
Undeceth-9 works by surrounding oil droplets with water-loving (hydrophilic) heads, allowing them to be suspended in water. This creates a stable emulsion and helps rinse away dirt, sebum, and makeup. In cleansers, it also boosts foam and improves the texture of the product.
Pros
Effective emulsifier
Undeceth-9 helps keep oil and water mixed, so your product stays smooth and doesn't separate on the shelf.
Improves cleansing
It boosts foam and helps remove excess oil and dirt, making it useful in shampoos and face washes.
Cons and cautions
Can be drying
Because it's a surfactant, it can strip natural oils from the skin, leading to tightness or dryness, especially with frequent use.
Potential irritation
In higher concentrations or for sensitive skin, it may cause mild redness or stinging.
Best for
- People with normal to oily skin looking for effective cleansers
- Those who use rinse-off products like shampoos and body washes
Use caution if
- Individuals with very dry, compromised, or eczema-prone skin
Usage tips
Safety summary
Undeceth-9 is considered safe for use in cosmetics at typical concentrations. It may cause mild irritation or dryness in sensitive individuals, especially in leave-on products. Regulatory bodies like the Cosmetic Ingredient Review (CIR) have evaluated similar PEG ethers and found them safe when formulated properly.
Research notes
Research on Undeceth-9 specifically is limited, but studies on similar PEG ethers indicate low acute toxicity and skin sensitization potential. The CIR has reviewed related ingredients and concluded they are safe for cosmetic use at typical levels.
Common label clues
- Typical concentration
- Typically 0.5–5% in rinse-off products; lower in leave-on formulas
- Regulatory status
- Approved for use in cosmetics in the US, EU, and many other regions, with concentration limits typically set by good manufacturing practices.
- Common uses
- Cleansers, Shampoos, Body washes, Emulsions
- Environmental note
- PEG-based surfactants can be slow to biodegrade in aquatic environments, though modern formulations often use lower concentrations.
Good to know
- Undeceth-9 is a PEG compound, which may be processed with ethylene oxide; however, cosmetic-grade versions are purified to safe levels.
- It is not typically used as a standalone ingredient but as part of a formulated blend.
Common questions
What is Undeceth-9 in beauty products?
Undeceth-9 is a synthetic ingredient that helps oil and water mix together in your skincare products. Think of it as a tiny bridge that keeps the formula from separating. It's often found in cleansers and shampoos to help them lather and rinse cleanly. While it's generally safe, it can strip natural oils if used too often, especially for dry or sensitive skin types.
What does Undeceth-9 do in a beauty product?
Undeceth-9 works by surrounding oil droplets with water-loving (hydrophilic) heads, allowing them to be suspended in water. This creates a stable emulsion and helps rinse away dirt, sebum, and makeup. In cleansers, it also boosts foam and improves the texture of the product.
Is Undeceth-9 safe for most people?
Undeceth-9 is considered safe for use in cosmetics at typical concentrations. It may cause mild irritation or dryness in sensitive individuals, especially in leave-on products. Regulatory bodies like the Cosmetic Ingredient Review (CIR) have evaluated similar PEG ethers and found them safe when formulated properly.
Who should be careful with Undeceth-9?
Individuals with very dry, compromised, or eczema-prone skin
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.