An attempt at product duplication

Back before I became a scientist, and before I had seriously considered what the word "natural" means, and before I was considering efficacy at the same level (or above) as "natural"-ness, there was a face wash I liked. It is called DermaMed Acne Wash. It has only four ingredients listed, so I thought it might be a good starting place for attempting a product duplication.

The ingredients are water, green tea extract, cocamidopropyl betaine, and salicylic acid. There is no preservative explicitly listed in the ingredients. It seems likely that the anti-acne ingredient, salicylic acid, is also serving as the preservative. This is a common trick used by "natural" products companies; they tend to use multi-purpose ingredients so they can claim "no preservatives," which is a silly claim to make if your consumers have even the vaguest knowledge of biology.

Salicylic acid is allowable in European cosmetic products as a preservative at up to 0.5% (reference); the consensus seems to be that it is bactericidal, and works against mould and fungi, but that its efficacy is dependent on the formulation.

So, I gave it a shot. I took a guess at how much surfactant (cocamidopropyl betaine, the ingredient that makes this a cleanser) they might have used, my guess was 16%. I knew the salicylic acid was 2%, because they have to state the concentration of active/medicinal ingredients. Extracts are generally used at 1-2% or less, so I went for 1%. And water makes up the rest.

I boiled up my water and mixed it with the other ingredients. I was doubtful about the salicylic acid dissolving nicely, since I'd seen it precipitate before. Surfactants can help with the solubility though, so I was willing to try. I put my definitely-not-the-same-colour-as-the-commercial-product concoction into a foamer bottle, since it was super runny (runnier than the store-bought version, probably meaning I had used less surfactant than they did), and went about my business. The commercial producer likely used a liquid green tea extract (and a green dye by the looks of things), while I was using a powdered extract, so that would account for the colour difference.

A while later I had a look at my bottle of stuff; it seemed like the surfactant and green tea were sticking together and separating out of the water. I gave it a shake and let it be. Overnight, the salicylic acid precipitated out of the solution.

I liked how smooth it made my skin feel, so I used it in spite of its shortcomings, just shaking it up before pumping some out so I wouldn't get a face-full of salicylic acid, but I only made 50 g and I doubt if I will try this recipe again without major modifications. It really does make me wonder how accurate the product labelling is.