Oleaminopropylamineth-3 HCl: properties, uses, INCI functions, safety, alternatives

Oleaminopropylamineth-3 HCl is a cationic surfactant and conditioning agent derived from oleic acid, primarily used in hair care and skin care formulations for its film-forming, antistatic, and smoothing effects. This molecule stands at the intersection between fatty acid-based surfactants and amine-functional conditioning agents, offering both lipophilic compatibility and aqueous solubility in its hydrochloride salt form.

Name breakdown

• Oleamino- → refers to a long-chain hydrophobic group derived from oleic acid (C18:1), a naturally occurring unsaturated fatty acid.

• Propylamino- → indicates a propyl-linked amine group, contributing to the molecule’s cationic nature.

• -eth-3 → signifies the presence of three ethoxylated (–CH₂CH₂O–) units, enhancing water solubility and flexibility.

• HCl → denotes that the compound is in its hydrochloride salt form, which stabilizes the amine group and improves aqueous solubility and formulation compatibility.

Together, these parts describe a cationic, amphiphilic conditioning agent with both lipophilic affinity (for hair and skin) and hydrophilic behavior, well-suited for cosmetic applications.

Molecular structure and reactivity

This compound features a multi-functional architecture that includes:

• A hydrophobic tail (typically C18, unsaturated, derived from oleic acid), which gives it excellent affinity for lipidic substrates such as skin and hair.

• A polyaminopropyl ethoxylated group, which contributes to cationic charge and electrostatic interaction with keratin structures (hair proteins are negatively charged at neutral pH).

• A protonated amine group (HCl salt), which stabilizes the molecule in aqueous media and enhances water solubility and compatibility with emulsions.

Functional groups present:

• Amine (–NH2) or quaternized amine

• Long-chain hydrocarbon (C18:1)

• Ether (–O–) from ethoxylation

• HCl as a counter-ion for the amine base

The molecule acts at the interface between hydrophilic and lipophilic phases, behaving similarly to a polymer-like conditioner with affinity for both oil and water.

Mechanism of action in hair products

In rinse-off and leave-on hair products, Oleaminopropylamineth-3 HCl works via:

• Electrostatic deposition: it binds ionically to negatively charged hair fibers, forming a thin film that resists rinsing.

• Hydrophobic coating: the fatty chain aligns along the hair surface, reducing friction, smoothing the cuticle, and preventing moisture loss.

• Antistatic effect: the cationic charge neutralizes static buildup, making hair less frizzy and more manageable.

• Conditioning synergy: often combined with silicones or polyquaterniums to enhance slip and softness.

Performance in formulations

Solubility and stability

• The HCl form is water-soluble, allowing easy incorporation into aqueous phases.

• Stable across a wide pH range, although optimal performance is typically around pH 4–6, matching the pH of hair and skin.

• Compatible with nonionic and cationic emulsifiers, but may be incompatible with strong anionic surfactants, which can precipitate cationic compounds.

Foam and cleansing

• Not primarily used as a cleanser or foaming agent.

• When present in shampoos, it improves feel and conditioning rather than increasing foam.

Specific cosmetic uses

Hair care

• Shampoos: reduces the harshness of primary surfactants, improves combability.

• Conditioners: enhances detangling and softness.

• Leave-in treatments: creates a smooth, touchable finish, especially effective on damaged, dry, or chemically treated hair.

• Hair masks and serums: offers occlusive protection against humidity and frizz.

Skin care

• Lotions and creams: acts as a conditioning agent that improves texture and enhances barrier function.

• After-shave balms or emulsions: reduces irritation, provides a soft, hydrated feel.

INCI functions

Surfactant - Emulsifying agent. Emulsions are thermodynamically unstable and are used to soothe or soften the skin and emulsify, so they need a specific, stabilising ingredient. This ingredient forms a film, lowers the surface tension and makes two immiscible liquids miscible. A very important factor affecting the stability of the emulsion is the amount of the emulsifying agent. Emulsifiers have the property of reducing the oil/water or water/oil interfacial tension, improving the stability of the emulsion and also directly influencing the stability, sensory properties and surface tension of sunscreens by modulating the filmometric performance.

 Comparison with similar compounds

Oleaminopropylamineth-3 HCl offers a balance between conditioning strength, mildness, and natural origin, being derived from vegetable fatty acids, but is an ethoxylated compound.

Toxicology and regulatory status

• Low dermal toxicity when used at appropriate concentrations (typically 0.1–2%).

• Non-irritating in most tested cosmetic use conditions.

• Should be tested in final formulation for skin compatibility and eye safety.

• Not restricted under EU or US regulations, but must be listed properly under INCI labeling requirements.

It is important to pay particular attention to ethoxylated products, which are chemical compounds treated with ethylene oxide, as potentially harmful residues may remain during the processing process. It is essential to choose high quality ethoxylated products rather than relying solely on price.

The term 'eth' refers to the ethoxylation reaction with ethylene oxide after which residues of ethylene oxide and 1,4-dioxane, chemical compounds considered carcinogenic, may remain (1). The degree of safety therefore depends on the degree of purity of the compound obtained. No manufacturer appears to provide this information on the label, at least as of the date of this review.

Environmental impact

• Biodegradability: moderate, depending on the ethoxylation level and fatty chain saturation.

• Ecotoxicity: relatively low in rinse-off applications, but caution is advised in leave-on or high-dosage industrial uses.

• Considered preferable to traditional quaternary ammonium compounds for formulators seeking greener profiles.

Conclusion

Oleaminopropylamineth-3 HCl is a versatile, amphiphilic, and bio-based cationic surfactant, offering effective conditioning, softening, and antistatic benefits in hair and skin formulations. Its combination of plant-derived fatty chains and cationic functional groups makes it a mild yet efficient alternative to harsher synthetic quats, suitable for modern, eco-conscious cosmetics.

References__________________________________________________________________________

(1) Kim MC, Park SY, Kwon SY, Kim YK, Kim YI, Seo YS, Cho SM, Shin EC, Mok JH, Lee YB. Application of Static Headspace GC-MS Method for Selective 1,4-Dioxane Detection in Food Additives. Foods. 2023 Sep 2;12(17):3299. doi: 10.3390/foods12173299. 

Abstract. "Efficient detection methods must be developed for 1,4-dioxane due to its suspected status as a human carcinogen, which is highly mobile in food and environmental resources. In this regard, this experiment has been conducted to develop reliable and selective detection and measurement methods by using static headspace (SH) isolation, followed by gas chromatography-mass spectrometry (GC-MS). A new method was developed for determining the spiked 1,4-dioxane contents in a polyethylene glycol 600 (PEG 600). The optimal condition for SH-GC-MS was discussed. The representative ions of 1,4-dioxane and 1,4-dioxane-d8 in the SIM mode of MS are 88 and 96, respectively, and the peaks of the SIM mode were separated and confirmed. The linear range for the method covers 0.25 to 100 mg/L with a coefficient of determination (R2) ≥ 0.999. The method applicability was demonstrated by spike recovery across a variety of food additives (i.e., chlorine bitartrate, choline chloride, polysorbate 20 and 60, and PEG 1000). All spike recovery from the tested samples was in the range of 89.50-102.68% with a precision of 0.44-11.22%. These findings suggest a new analytical method for food safety inspection, and could be applicable for ensuring the safety of foods and environmental and public health on a broad scale."