What Is C11-15 Alketh-9?
C11-15 Alketh-9 is a man-made ingredient created by attaching about nine units of ethylene oxide to a blend of synthetic fatty alcohols that contain 11 to 15 carbon atoms. This process turns oily alcohols into a water-loving substance, giving the material both oil-friendly and water-friendly ends. Originally known as C11-15 Pareth-9, it has been part of cosmetic chemistry since the late 1970s when formulators began looking for gentle yet effective alternatives to older detergents.
The ingredient is produced through a two-step method. First chemists make the base fatty alcohols in a lab setting, often starting from petrochemical feedstocks or plant-based oils that have been refined and shortened. Next they react these alcohols with controlled amounts of ethylene oxide gas inside pressurized reactors. Careful temperature and time controls let them reach the desired average of nine ethylene oxide units, which defines the “-9” in the name.
Because it can mix oil and water, C11-15 Alketh-9 shows up in many topical products. You will most often find it in facial cleansers, body washes, lotions, creams, makeup removers, exfoliating scrubs, clay or sheet masks and leave-on serums. It also plays a role in sunscreens and anti-aging moisturizers where it keeps the formula smooth and stable.
C11-15 Alketh-9’s Cosmetic Benefits/Uses
In everyday skin and hair care formulas this ingredient serves one clear purpose that brings several benefits.
Emulsifying: C11-15 Alketh-9 helps oil and water stay blended so the product remains uniform from the first pump to the last. A stable emulsion feels nicer on the skin, delivers active ingredients evenly and prevents separation during shipping or storage. This stability also lets brands cut down on heavy waxes or extra thickeners, leading to lighter textures that absorb faster and rinse off more cleanly.
Who Can Use C11-15 Alketh-9
Because C11-15 Alketh-9 is mainly an emulsifier and is used at low levels, it suits most skin types including normal, oily, combination and even dry skin, since it does not strip oils on its own. Very sensitive or reactive skin may feel a slight sting if the formula contains a high percentage of surfactants, but that reaction is tied more to the overall product than to this ingredient alone.
The raw material is produced from synthetic or plant-derived feedstocks and involves no animal by-products, so it is considered appropriate for vegans and vegetarians.
No data indicate that topical use causes problems for pregnant or breastfeeding women when the ingredient is used as intended in cosmetics. This is not medical advice and anyone who is pregnant or nursing should review all personal care products with a healthcare provider to stay on the safe side.
C11-15 Alketh-9 does not increase photosensitivity and can be worn under sunscreen or makeup without making skin more prone to sun damage.
Potential Side Effects/Adverse Reactions
Responses to any cosmetic ingredient vary by individual. The effects listed below are possible but uncommon when C11-15 Alketh-9 is used in a properly formulated product.
- Mild skin irritation temporary redness, itching or stinging, more likely on very sensitive skin or with leave-on products that use higher amounts
- Contact allergy rare cases of rash or hives in people already prone to polyethylene glycol allergies
- Dryness or tightness if a formula relies heavily on detergents and lacks replenishing ingredients
- Eye irritation watering or burning sensation if the product accidentally gets into the eyes
If any of these reactions occur stop using the product and seek advice from a medical professional.
Comedogenic Rating
Rating: 1/5 C11-15 Alketh-9 sits low on the comedogenic scale because it is used at small concentrations and its molecular size keeps it on the skin surface where it helps oil and water mix rather than sinking into pores. It lacks the heavy, waxy character that typically plugs follicles. Most formulas that include it rinse or wipe away easily further lowering clogging risk. This makes it generally suitable for skin that is prone to acne or breakouts. Only in very rich leave-on products combined with other pore-clogging ingredients could it contribute indirectly to congestion.
Summary
C11-15 Alketh-9 is mainly an emulsifier that keeps oil and water phases evenly blended so products stay smooth, stable and pleasant to use. It does this by carrying a water-loving end and an oil-loving end within the same molecule allowing it to sit at the oil-water boundary and hold both sides together. You will see it in cleansers, lotions, masks and sunscreens although it is not as famous as some newer naturally derived emulsifiers so its presence on ingredient lists is steady but not headline-grabbing.
The ingredient has a long track record in cosmetics with low rates of irritation or allergy when used at the percentages common for emulsification. Overall safety is considered high yet every skin type is different so it is wise to patch test any new product that contains C11-15 Alketh-9 before adding it to your routine.