What Is C11-15 Pareth-9?
C11-15 Pareth-9 is a synthetic ingredient made by attaching roughly nine units of ethylene oxide to fatty alcohols that contain between eleven and fifteen carbon atoms. Those fatty alcohols usually come from plant oils like coconut or from petroleum fractions. The result is a clear to slightly hazy liquid that mixes well with both oil and water.
Ethoxylated fatty alcohols first appeared in household cleaners in the mid-20th century, and cosmetic chemists quickly adopted them because they clean skin without stripping it as harshly as older soaps. Over time the specific blend known as C11-15 Pareth-9 proved handy in personal care products, earning a spot on ingredient lists in the 1970s and it has remained popular since.
The manufacturing process starts with purified fatty alcohols. These are fed into a reactor where pressurized ethylene oxide gas is added in the presence of a basic catalyst. Careful control of temperature and pressure determines how many ethylene oxide units attach, with nine being the average for this material. After neutralization and filtration the liquid is ready for use in formulas.
You will most often find C11-15 Pareth-9 in facial cleansers, micellar waters, makeup removers, exfoliating masks, lightweight moisturizers, sunscreens, leave-on hair treatments and some anti-aging serums that need stable oil-in-water emulsions.
C11-15 Pareth-9’s Cosmetic Benefits/Uses
Formulators choose C11-15 Pareth-9 because it pulls double duty in many products.
- Cleansing: Its surfactant action lifts away excess oil, sunscreen, makeup and daily grime then lets them rinse off with water, leaving skin and hair feeling clean yet comfortable
- Emulsifying: It helps keep water and oil ingredients blended so creams, lotions and serums stay smooth, stable and pleasant to apply throughout their shelf life
Who Can Use C11-15 Pareth-9
C11-15 Pareth-9 is generally well tolerated by most skin types. Oily and combination skin benefit from its cleansing power while normal and dry skin usually find it gentle enough for daily use. People with very dry or eczema-prone skin should watch for any extra tightness because surfactants can sometimes remove too much natural oil if a formula is poorly balanced.
The ingredient is synthetic and normally produced from coconut or petroleum sources so it contains no animal‐derived material. That makes it suitable for vegans and vegetarians as long as the finished product is certified cruelty free by the brand.
C11-15 Pareth-9 has a long record of safe use during pregnancy and breastfeeding with no evidence of absorption into the bloodstream. This is not medical advice and anyone who is pregnant or nursing should confirm any skincare routine with a qualified doctor to be sure it suits their personal situation.
It does not make skin more sensitive to sunlight and there are no known interactions with common topical actives like retinoids or vitamin C. It also rinses readily so it is safe for daily use in both face and body products.
Potential Side Effects/Adverse Reactions
Reactions to C11-15 Pareth-9 vary from person to person. The following are potential side effects that could occur, though most users will not experience them when the ingredient is used at the levels allowed in cosmetics.
- Mild skin irritation such as stinging or burning, especially on compromised skin
- Temporary redness, flaking or itching from over-cleansing
- Allergic contact dermatitis in rare cases of true allergy to ethoxylated compounds
- Eye irritation if a facial cleanser or shampoo containing the ingredient seeps into the eyes
- Scalp or hair dryness when used in very high concentrations or left on for prolonged periods
If any of these effects occur stop using the product and seek advice from a healthcare professional or dermatologist.
Comedogenic Rating
Rating: 1 out of 5
C11-15 Pareth-9 is an emulsifying cleanser that is water soluble and typically used at low levels in formulas that rinse off. Because it does not leave an oily film on the skin and is quickly removed with water, it is very unlikely to clog pores. The small chance of buildup in a leave-on product is why it is given a 1 rather than a perfect 0.
This low score means the ingredient is generally suitable for acne-prone or breakout-prone skin. Only those who react to most surfactants or who use very heavy leave-on products may need to be cautious.
No known data suggest that C11-15 Pareth-9 worsens fungal acne or interferes with common acne treatments.
Summary
C11-15 Pareth-9 works as both a cleanser and an emulsifier. Its surfactant side loosens dirt, oil and makeup so they rinse away with water while its emulsifying side keeps water and oil blended in creams, lotions and serums so the formula stays smooth and stable.
The ingredient has been on cosmetic shelves since the 1970s and remains a quiet staple. You will not see it marketed as a star active yet it shows up in a wide range of cleansers, micellar waters, sunscreens and light lotions because it gets the job done without fuss.
Safety reviews find it mild for most users when used at the levels allowed in personal care products. Serious reactions are rare and the ingredient does not build up in the body. As with any new product a simple patch test is wise to confirm your skin agrees with the full formula before regular use.