Undeceth-8: What Is It, Cosmetic Uses, Benefits & Side Effects

Curious about this ingredient? In this article we're explaining exactly what it is and why it's used within cosmetic formulations.
Updated on: June 30, 2025
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We verify all information on this page using publicly available nomenclature standards from The Personal Care Products Council (PCPC), the European Commission's CosIng database and documentation provided directly by ingredient manufacturers. Our analysis is based on technical data from these sources to ensure accuracy and reliability.

What Is Undeceth-8?

Undeceth-8 is a synthetic ingredient created by reacting undecyl alcohol, a fatty alcohol often sourced from plant oils like coconut or castor, with about eight units of ethylene oxide. The result is a clear lightweight liquid that blends water friendly and oil friendly parts in one molecule. This balance lets it mix oily ingredients with water, making formulas smoother and easier to rinse. Chemists began exploring these ethoxylated fatty alcohols in the late 1960s as gentler alternatives to harsh soaps, and Undeceth-8 soon found a spot in personal care labs thanks to its mildness and versatility. Production happens in closed reactors where controlled amounts of ethylene oxide attach to the fatty alcohol, followed by purification to remove residues. You will typically spot Undeceth-8 in facial cleansers, micellar waters, makeup removers, lightweight moisturizers, sheet masks, hair conditioners and even some anti aging serums that need a soft, non greasy finish.

Undeceth-8’s Cosmetic Benefits/Uses

Formulators reach for Undeceth-8 because it can play more than one helpful role in a single recipe.

  • Skin conditioning: Leaves a soft hydrated feel on the skin surface so products feel comfortable rather than tight
  • Emollient: Helps fill in tiny gaps between skin cells giving a smoother appearance and reducing flakiness
  • Cleansing: Lifts away dirt oil and makeup while staying mild enough for daily use
  • Emulsifying: Keeps water based and oil based ingredients mixed together so the product stays stable and pleasant to use

Who Can Use Undeceth-8

Because it is mild and non occlusive Undeceth-8 suits most skin types including dry sensitive combination and oily. Dry skin benefits from its light emollient feel while oily or acne prone skin usually tolerates it since it does not leave a heavy residue. Only those with a known sensitivity to ethoxylated ingredients might need caution.

The fatty alcohol used to make Undeceth-8 is usually sourced from coconut castor or synthetic feedstocks rather than animal fat which makes the final ingredient generally suitable for vegans and vegetarians. Anyone following a strict lifestyle should still check with the specific brand to confirm plant derived sourcing and cruelty free processing.

Current safety assessments show no special risk for pregnant or breastfeeding users when Undeceth-8 is applied to intact skin. This is not medical advice and anyone who is pregnant or nursing should clear new skincare products with a qualified doctor just to be safe.

Undeceth-8 does not increase photosensitivity so it will not make skin more prone to sunburn. It is also odorless colorless and free of common allergens like gluten or nuts which is worth noting for people with those concerns.

Potential Side Effects/Adverse Reactions

Reactions to topical Undeceth-8 differ from person to person. The points below outline potential issues that could occur although most users will not experience them when the ingredient is properly formulated.

  • Mild skin irritation transient stinging or redness can occur especially on damaged or very sensitive skin
  • Contact dermatitis rare allergic response may lead to itching rash or swelling
  • Eye irritation undiluted or high levels may cause tearing or burning if the product accidentally gets into the eyes
  • Dryness over cleansing with products rich in Undeceth-8 can strip natural oils in some users leading to a tight feeling

If you experience any of these effects stop using the product and seek guidance from a healthcare professional.

Comedogenic Rating

Rating: 1/5
Undeceth-8 is a lightweight water-soluble surfactant with no heavy oils or waxes that could lodge in pores. It rinses off cleanly and does not leave an occlusive film so the chance of clogging is very low. A small portion of fatty alcohol remains in the molecule but its level is not enough to raise the score beyond a 1.

Generally considered suitable for acne prone or breakout prone skin.

No formal pore-clogging studies exist specifically for Undeceth-8 yet decades of use in facial cleansers and micellar waters without congestion complaints support the low rating.

Summary

Undeceth-8 works as a skin conditioning agent, mild cleanser, emollient and emulsifier. Its balanced water loving and oil loving ends let it dissolve grime, smooth rough areas and keep water and oil phases blended while leaving a non greasy finish.

You will spot it in a fair number of modern cleansers, micellar waters and light lotions though it is not as instantly recognizable as blockbuster surfactants like Polysorbate 20.

Safety assessments and real-world use show a low irritation profile and minimal allergy risk. Still, when trying any new product that contains Undeceth-8 it is wise to carry out a brief patch test to make sure your skin agrees with the formula.

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