Preservative, and why a water-based cleaner needs one

The ingredient every water-based cleaner needs, that nobody thinks about, and that must not be advertised.

Water grows things

A water-based product is a nutrient-bearing aqueous system at room temperature. Bacteria, yeasts and molds grow in it.

The surfactants, the thickener, the fragrance and any plant-derived material are all food. A "natural" formula is frequently a better growth medium than a synthetic one, not a worse one.

And the product is opened, used with wet hands, and refilled, which reinoculates it repeatedly.

What fails without one

Cloudiness, then a smell, then visible growth or a film.

Viscosity loss, as microbes break down the thickener.

And a product that a customer will photograph, because growth in a cleaning product is the most alarming-looking failure in this category.

It does not always show. A contaminated product can look and smell normal, which is why the test is a challenge test rather than a look.

Choosing one

Match it to the pH of your formula: several common preservatives work only in a narrow band, and a strongly alkaline or strongly acidic product rules most of them out.

Check compatibility with your surfactants, particularly cationics.

Use the supplier's stated level. Under-dosing is the commonest failure and it produces a product that survives the shelf and fails in the customer's cupboard.

A chelator helps, because free metal ions reduce preservative efficacy.

And note the products that need less: very high or very low pH, high solvent content, or very high surfactant concentration are all hostile to growth in themselves, which is why a caustic degreaser is a different case from a gentle all-purpose spray.

Keep it off the front of the label

This is the compliance point and it matters.

A preservative protects the product in the bottle. Promoting it as a benefit to the user is an antimicrobial claim, and it is the route by which a compliant cleaner becomes an unregistered pesticide.

It belongs in the ingredient list and nowhere else.

References