What Is Undeceth-9?
Undeceth-9 is a synthetic ingredient made by joining undecyl alcohol, a fatty alcohol with 11 carbon atoms, to a chain of ethylene oxide units. The “9” in its name tells you that the average chain holds nine of these units. The result is a clear liquid that loves both water and oil, which makes it a handy helper in many formulas.
Chemists began exploring fatty alcohol and ethylene oxide blends in the mid-20th century while looking for mild cleansers that would not strip the skin. Over time the balance of safety, mildness, and versatility pushed Undeceth-9 into mainstream personal care labs. Today most batches are produced by reacting plant-derived undecyl alcohol with controlled amounts of ethylene oxide under heat and pressure, then purifying the mix to remove any leftover raw materials.
You will most often spot Undeceth-9 in rinse-off items like facial cleansers, body washes, and shampoos, but it also slips into leave-on products. Lightweight moisturizers, facial masks, anti-aging gels and even some hair conditioning sprays rely on it to keep oil- and water-based parts smoothly blended while adding a soft touch to skin and hair.
Undeceth-9’s Cosmetic Benefits/Uses
Formulators reach for Undeceth-9 because it can play several helpful roles in one bottle.
- Skin Conditioning: Leaves a light, smooth feel on the skin making finished products feel more elegant and helping skin hold on to moisture
- Emollient: Softens and helps fill in tiny surface gaps so skin feels silky and looks healthy
- Cleansing: Lifts away dirt, oil and buildup without harshness which supports gentle daily cleansing routines
- Emulsifying: Keeps oil and water ingredients mixed so lotions stay stable and clear gels do not separate over time
Who Can Use Undeceth-9
Thanks to its gentle nature and lightweight feel, Undeceth-9 generally suits normal, oily, combination and dry skin. Sensitive skin usually tolerates it as well because it has low irritation potential and is often used in mild baby cleansers. Those with a history of contact dermatitis to synthetic surfactants should still pay attention to ingredient lists but most people experience no redness or stinging.
Undeceth-9 is typically made from plant derived fatty alcohol and a petrochemical based ethylene oxide chain so no animal sourced components are involved. That makes finished products containing it acceptable for vegans and vegetarians provided the rest of the formula is also free of animal ingredients or by-products.
Current safety data do not flag Undeceth-9 as a risk for pregnancy or breastfeeding when used in rinse off or leave on cosmetics. It is absorbed through skin in only trace amounts and has not shown reproductive toxicity in available studies. This is not medical advice and anyone who is pregnant or nursing should review all skincare choices with a qualified healthcare professional.
The molecule does not increase skin sensitivity to sunlight so it is not regarded as photosensitising. It is also odorless and free of common perfume allergens which helps keep fragrance related flare ups in check.
Potential Side Effects/Adverse Reactions
Individual responses to any cosmetic ingredient can differ. The effects listed below are uncommon but possible when Undeceth-9 is applied to the skin. In well formulated products most users will not notice any of these issues.
Transient stinging or tingling
Mild redness or itching in very sensitive skin
Contact dermatitis in rare cases of surfactant allergy
Eye irritation if the product accidentally gets into eyes
If irritation, swelling or persistent discomfort develops stop using the product and seek advice from a healthcare provider.
Comedogenic Rating
Rating: 1 / 5
Undeceth-9 is mostly water soluble and used at low levels, so it rinses clean without leaving an oily film that could block pores. Its undecyl backbone is short enough to avoid heavy residue and the nine ethylene oxide units make the molecule highly dispersible in water. Together these traits keep the risk of pore clogging very low.
Suitable for acne-prone or breakout-prone skin in most cases.
No standard comedogenicity studies have singled out Undeceth-9, yet the structure is similar to other ethoxylated fatty alcohols that consistently test as non comedogenic. Very occlusive bases or heavy silicones in the same formula will have a much bigger impact on pore blockage than this ingredient itself.
Summary
Undeceth-9 conditions skin, acts as a mild cleanser, softens with emollient slip and keeps oil and water smoothly blended. It manages these jobs by pairing an 11-carbon tail that grabs oils with nine ethylene oxide units that bond with water, letting it sit comfortably at the border of both phases.
It is a familiar workhorse in labs though not a headline ingredient. You will find it scattered through gentle cleansers, light lotions and some hair sprays where formulators need reliable performance without adding weight.
Current data show it to be low risk for irritation, allergy or toxicity in the concentrations used in cosmetics. As with any new product do a quick patch test first to make sure your skin agrees with the full formula.