What Is Undecylenamidopropyltrimonium Methosulfate?
Undecylenamidopropyltrimonium Methosulfate is a specialty conditioning agent made by joining undecylenic acid, a fatty acid from castor or coconut oil, with a small nitrogen-containing compound called propylamine, then quaternizing it with methyl sulfate. The result is a water-soluble molecule that carries a gentle positive charge, letting it cling to hair and skin. First explored in the late 1990s as chemists searched for milder alternatives to traditional quats, it quickly found favor thanks to its dual ability to fight microbes and smooth static. Manufacturing starts with plant-derived undecylenic acid that is reacted in a controlled, low-temperature process to form the amide backbone, followed by a quaternization step that locks in its conditioning charge. Today you will spot this ingredient in rinse-off and leave-on hair masks, shampoos, co-washes, anti-frizz serums, scalp treatments, mild body washes and some deodorizing creams.
Undecylenamidopropyltrimonium Methosulfate’s Cosmetic Benefits/Uses
Formulators choose this ingredient because it tackles several needs at once, helping products feel nicer and stay fresher.
- Antimicrobial: Its undecylenic acid side chain disrupts the growth of odor-causing bacteria and some fungi, so it helps keep formulas microbially stable and leaves the scalp or skin feeling clean
- Antistatic: The positive charge neutralizes static electricity on hair strands, cutting down on flyaways and giving hair a smoother, more manageable finish
- Hair conditioning: It forms a light, breathable film that boosts softness, adds slip for easier combing and provides a subtle protective barrier against environmental stress
Who Can Use Undecylenamidopropyltrimonium Methosulfate
This conditioning agent is gentle enough for most skin and hair types, including sensitive, dry and oily. Its water-soluble nature means it rinses clean without leaving a heavy residue, so those prone to breakouts or scalp build-up usually tolerate it well. People with very reactive skin or a known sensitivity to quaternary ammonium compounds should proceed with caution, as rare irritation can occur.
Undecylenamidopropyltrimonium Methosulfate is typically sourced from plant oils like castor or coconut, with no animal by-products used in standard production. That makes it suitable for vegans and vegetarians, though ingredient sourcing can vary by supplier so strict lifestyle users may wish to confirm with the brand.
No studies have flagged this ingredient as unsafe during pregnancy or while breastfeeding. It is not absorbed deeply into the skin or known to affect hormones. Still, this is not medical advice and expectant or nursing mothers should run any new product past their doctor just to be safe.
The molecule is not photosensitizing, so it will not make skin more sensitive to sunlight. It is color-safe for dyed hair and works well in curly and chemically treated styles, providing slip without stripping treatments.
Potential Side Effects/Adverse Reactions
Reactions to topical Undecylenamidopropyltrimonium Methosulfate vary from person to person. The points below outline potential side effects but most users will not experience them when the ingredient is used correctly in a well-formulated product.
- Mild skin or scalp irritation, especially on broken or highly sensitive skin
- Allergic contact dermatitis in individuals sensitive to quaternary ammonium compounds
- Temporary eye irritation if the product accidentally gets into the eyes
- Weighed-down feel or greasiness on very fine hair if overapplied in leave-on products
- Reduced conditioning performance when mixed with high levels of strong anionic surfactants, potentially leading to dryness
If any adverse effect occurs stop using the product and consult a healthcare professional or dermatologist.
Comedogenic Rating
Rating: 1 / 5
Although Undecylenamidopropyltrimonium Methosulfate originates from a fatty acid, the finished molecule is water soluble and carries a positive charge that keeps it from building up in pores. It forms only a light, breathable film and rinses away easily, so it rarely traps oil or debris. Because of this low likelihood of clogging pores, it is generally fine for people prone to acne or breakouts. Its mild antimicrobial action may even discourage the growth of blemish-causing bacteria. Only in very heavy leave-on formulas or when paired with occlusive oils could it potentially contribute to congestion.
Summary
Undecylenamidopropyltrimonium Methosulfate works as an antimicrobial, antistatic and hair-conditioning agent. The undecylenic acid side chain weakens microbial cell membranes, helping keep products fresh and skin or scalp balanced. Its quaternary ammonium head carries a gentle positive charge that neutralizes static on hair, smooths cuticles and lays down a thin conditioning layer that boosts softness and slip.
While not as common as mainstream conditioning quats like behentrimonium chloride, it has carved out a steady niche in gentle shampoos, co-washes and leave-in sprays where brands want a lighter feel and an added touch of antimicrobial defense.
Safety profiles and decades of cosmetic use show it to be low risk for most users, with irritation and allergy reported only rarely. As with any new ingredient, it is wise to patch test a product first to be sure your skin or scalp agrees with it.