What Is C11-15 Alketh-15?
C11-15 Alketh-15 is a synthetic ingredient made by reacting a blend of medium-chain fatty alcohols that contain 11 to 15 carbon atoms with about 15 units of ethylene oxide. The result is a polyethylene glycol ether that dissolves well in both water and oil, which is why formulators like it. First introduced in the 1970s as C11-15 Pareth-15, it gained popularity when cosmetic chemists searched for milder, more versatile alternatives to older emulsifiers that could feel heavy or greasy. The production process starts with petroleum or plant-derived fatty alcohols, which are purified then combined with ethylene oxide under controlled heat and pressure to build those 15 repeating units. Because the feedstocks and reaction conditions can be closely monitored, the final material is consistent from batch to batch.
You are most likely to find C11-15 Alketh-15 in light lotions, facial moisturizers, sunscreens, hair conditioners, cleansing balms, sheet mask essences and creamy wash-off masks. Its ability to help water and oil stay mixed makes it especially handy in anti-aging serums that contain both nourishing oils and water-borne actives, as well as in styling creams that need to stay smooth in a humid bathroom.
C11-15 Alketh-15’s Cosmetic Benefits/Uses
C11-15 Alketh-15 serves a single but important job in formulas
Emulsifying: It binds water and oil into a stable blend so a cream does not separate in the jar or on your skin. By creating a uniform texture it improves spreadability, ensures each application delivers the same level of active ingredients and leaves a lighter, more pleasant skin feel.
Who Can Use C11-15 Alketh-15
C11-15 Alketh-15 is generally considered suitable for all skin types, including dry, oily and sensitive, because it has a low risk of clogging pores and a mild action on the skin’s surface. People with very reactive or allergy-prone skin may still wish to monitor how their skin feels when first using a product that contains it, as they would with any new ingredient.
The ingredient is synthetic and can be sourced from either petroleum or plant-based fatty alcohols, so it is typically classified as vegan and vegetarian friendly. Brands that promote cruelty-free values also tend to accept it because it is not animal derived.
There are no known issues for women who are pregnant or breastfeeding when C11-15 Alketh-15 is applied topically at the low levels used in cosmetics. This is not medical advice, and anyone who is pregnant or nursing should check with a healthcare professional before adding new skincare products to their routine.
C11-15 Alketh-15 does not make skin more sensitive to the sun, so it does not increase the need for extra sun protection beyond the usual recommendations.
Potential Side Effects/Adverse Reactions
Reactions to topical C11-15 Alketh-15 differ from person to person. The points below outline possible side effects, but most people will not experience them when the ingredient is used correctly in a well-formulated product.
- Mild skin irritation, especially on very sensitive or damaged skin
- Allergic contact dermatitis in rare cases of individual sensitivity
- Eye stinging or redness if the product accidentally gets into the eyes
- Dry or tight feeling if the formula contains a high concentration and the skin barrier is already compromised
- Trace contamination with 1,4-dioxane if manufacturing purification is inadequate, though reputable suppliers keep levels far below regulatory limits
If you notice any of these reactions, stop using the product and consult a healthcare professional if discomfort persists.
Comedogenic Rating
Rating: 1/5. C11-15 Alketh-15 is highly water soluble and usually used at low levels, so it tends to rinse clean without leaving a heavy film that could block pores. Its molecular structure is larger than typical fatty acids that trigger breakouts, giving it little chance to lodge inside follicles. For these reasons it is generally suitable for acne-prone or breakout-prone skin. If a formula is very rich or paired with heavier oils the overall product could still feel occlusive, but the emulsifier itself is unlikely to be the culprit.
Summary
C11-15 Alketh-15 is an emulsifier that keeps water and oil evenly blended, improves spreadability and helps formulas stay consistent from the first dip to the last. It does this by positioning its water-loving polyethylene glycol side in the watery phase while its fatty alcohol side grabs on to oils, forming a bridge that locks the two together. The ingredient has been around for decades, valued by chemists who want a dependable workhorse that feels light and plays well with a wide range of actives, though it has never been a headline-grabbing star ingredient.
Safety reviews show it is low risk for irritation when used at the small percentages common in cosmetics. As with any new skincare ingredient it is smart to patch test a fresh product to be sure your skin agrees with the full formula.