Euxyl K903, Natural Preservative, 10 ml

Euxyl K903 is a liquid broad-spectrum preservative for cosmetics with an acidic pH. It protects water-containing products against bacteria, yeasts and moulds and is used in creams, lotions, shampoos, shower gels and wet wipes, that is, in both rinse-off and leave-on products. The manufacturer developed it for formulations with a pH up to 6 and according to its data it is effective particularly in non-ionic systems.

The base of the blend is benzyl alcohol supplemented with benzoic acid and dehydroacetic acid; the blend also contains tocopherol. The raw material is synthetic, but according to the manufacturer the composition meets the requirements of several natural and certified cosmetics standards. The preservative is paraben-free and holds Vegan and Halal certifications.

Key properties

• Broad spectrum of activity – according to the manufacturer it acts evenly against bacteria, yeasts and moulds.
• Activity in the vapour phase too – the manufacturer reports good efficacy also in the headspace above the product surface.
• Leave-on and rinse-off products – the same raw material for a cream, toner, shampoo and shower gel.
• Wet wipes – the manufacturer also recommends it for emulsions and solutions used for saturating wipes.
• Liquid form – measured and blended without dissolving a powder; added only to the cooled phase.
• Readily biodegradable – according to OECD 301.

Use in formulation

The recommended dosage is 0.4–1.2 % by weight of the finished product. In the manufacturer's tests, 0.8 % was sufficient in a natural face cream at pH 5.5 to meet challenge test criteria. For an emulsion for wet wipes, 0.4 % was insufficient against moulds and full protection was only achieved at 0.8 %. Therefore confirm the final dose by challenge-testing the specific formulation. According to the manufacturer, minimum inhibitory concentrations for individual microorganisms are around 0.5–0.75 %; only for Staphylococcus epidermidis is a concentration above 1 % required.

The preservative is added during the cooling phase at a temperature below 80 °C, that is, after the emulsion has been formed, while the mass is still fluid and can be mixed thoroughly. It dissolves in alcohol and glycols, only partially in water. In emulsions and surfactant systems this is not an issue. In purely aqueous products such as toners or hydrolat sprays, pre-dissolving in a glycol, for example propanediol, or in a small amount of alcohol and then checking that the result is clear will help.

The most important parameter is pH. The blend is designed for formulations with a pH up to 6, and staying within this limit is recommended for reliable efficacy. For products with a higher pH, efficacy is not guaranteed and the pH must be adjusted before adding the preservative. It is compatible with non-ionic, anionic and cationic surfactants, making it usable in shampoos, conditioners and shower gels.

Good to know

The preservative protects the product but cannot substitute for production hygiene. The manufacturer states that it requires at least 48 hours of contact to destroy microorganisms in an already contaminated product. Therefore work with clean containers, sanitised equipment and raw materials with a low microbial load.

At temperatures below 5 °C the blend may solidify or crystals may form in it. This is not a sign of degradation. It is sufficient to warm the container gently to 40–45 °C, mix the contents thoroughly and only then measure out the dose. The raw material has a characteristic odour; in unscented products therefore check whether it is perceptible at the chosen dose.

Benzyl alcohol is among the fragrance allergens listed in Annex III of Regulation (EC) No 1223/2009, so when labelling the finished product include it in the ingredient list in accordance with the applicable limits. The concentrate is subject to CLP classification as a hazardous substance with pictograms for corrosivity, irritation and serious health hazards; details are in the safety data sheet.

Suitable for products such as

• Face and body creams and lotions – O/W emulsions with an acidic pH, where the manufacturer demonstrated full protection at 0.8 % already at pH 5.5.
• Shampoos, shower gels and conditioners – surfactant systems with an acidic pH; compatible with all types of surfactants.
• Toners and hydrolat sprays – after pre-mixing in a glycol or alcohol and checking clarity.
• Wet wipes – impregnation emulsions and solutions, where the manufacturer achieved full protection at 0.8 %.
• Decorative cosmetics – aqueous formulations with a pH below 6.

Frequently asked questions