What Is C9-11 Alketh-6 Carboxylic Acid?
C9-11 Alketh-6 Carboxylic Acid is a synthetic fatty acid derived from natural oils rich in medium-chain alcohols, typically coconut or palm kernel oil. Chemically it is an ethoxylated carboxylic acid where the alkyl chain length ranges from nine to eleven carbon atoms and carries an average of six ethylene oxide units. This structure gives the molecule a water-loving head and an oil-loving tail, a balance that makes it an effective surface-active agent.
The ingredient emerged in the late 1970s when formulators were searching for milder alternatives to traditional soap-based cleansers. By reacting C9-11 fatty alcohols with ethylene oxide and then carboxylating the resulting ethoxylate, chemists created a compound that offers good cleansing power while staying gentle on skin. Today the process is carried out in controlled reactors where temperature, pressure and pH are carefully managed to achieve the desired average of six ethoxy groups before a final oxidation step introduces the carboxylic acid function.
You will most often see C9-11 Alketh-6 Carboxylic Acid in rinse-off products such as facial cleansers, body washes, micellar waters and exfoliating masks. It may also appear in some light lotions, make-up removers and scalp scrubs where a mild yet effective cleansing boost is needed without stripping the skin or hair.
C9-11 Alketh-6 Carboxylic Acid’s Cosmetic Benefits/Uses
In cosmetic formulas this ingredient serves a single but valuable purpose: cleansing. Its amphiphilic structure lowers the surface tension of water, helping the product spread easily and lift away dirt, excess oil and make-up. Because the molecule is smaller and less alkaline than traditional soaps it tends to rinse cleanly and leaves the skin feeling soft rather than tight, making it a popular choice for gentle daily cleansers and products aimed at sensitive or dry skin types.
Who Can Use C9-11 Alketh-6 Carboxylic Acid
This cleanser is generally well tolerated by most skin types including oily, combination, normal and even sensitive skin thanks to its mild, soap-free nature. Very dry or barrier-impaired skin can still use it but may need a richer follow-up moisturizer because any surfactant has the potential to lift some natural oils.
The ingredient is produced from plant-derived alcohols and petrochemical ethylene oxide with no animal by-products, so it is suitable for vegans and vegetarians. Those avoiding palm resources for sustainability reasons may want to check with individual brands about sourcing.
No data suggest the molecule poses specific risks during pregnancy or breastfeeding. That said, this is not medical advice and pregnant or nursing individuals should run any skincare products past a doctor to be safe.
C9-11 Alketh-6 Carboxylic Acid does not make skin more sensitive to sunlight and has no known interactions with common topical actives such as vitamin C, niacinamide or retinoids.
Potential Side Effects/Adverse Reactions
Reactions vary from person to person. The points below list potential side effects, but most users will not experience them when the ingredient is formulated and used as intended.
- Mild eye stinging or watering if the cleanser accidentally gets into the eyes
- Temporary dryness or tightness, more noticeable with frequent washing or in low humidity
- Rare cases of redness, itching or allergic contact dermatitis in individuals sensitive to ethoxylated ingredients
- Scalp irritation when used in high concentrations in shampoos for very reactive scalps
If irritation or any other negative effect occurs, stop using the product and seek guidance from a healthcare professional or dermatologist.
Comedogenic Rating
Rating: 1 / 5
C9-11 Alketh-6 Carboxylic Acid is a water-soluble surfactant that is usually used in rinse-off products, so it spends very little time sitting on the skin where it could block pores. Its molecule is small, not waxy and easily removed with water, which keeps pore-clogging potential low. For acne-prone or breakout-prone skin this ingredient is generally considered safe thanks to its quick rinse-off nature and minimal residue.
Because it belongs to the ethoxylated fatty acid family, people with extremely reactive or occlusion-sensitive skin might still prefer to check how their skin feels after use, especially if the product contains other heavier ingredients.
Summary
C9-11 Alketh-6 Carboxylic Acid works as a mild cleanser that lifts dirt, oil and make-up by pairing an oil-loving tail with a water-loving head, letting grime mix with water and rinse away without stripping the skin. It appears most often in face washes, body cleansers and micellar waters where a gentle yet effective surfactant is needed.
The ingredient sits in the middle ground of popularity: common enough to be found in several gentle cleansers yet not as ubiquitous as household names like sodium laureth sulfate. Formulators reach for it when they want cleaning power with a softer after-feel.
Safety data show a low irritation profile and a very low risk of clogging pores. Still, skin is personal so it is wise to patch test any new product that contains C9-11 Alketh-6 Carboxylic Acid before adding it to a full routine.