Update, September 2026. This article was written in August, before our test result came back. It has been corrected. The original said testing was still under way. It is not.
A preservative efficacy test deliberately contaminates a product with bacteria, yeast and mould, then measures over 28 days whether the formula kills them. It is what stands between a jar that has been open for three months in a warm bathroom and a jar you should not put on your face. We have that result for our product. It is in our file, from an accredited laboratory, and the product passes.
The test exists because of how products are actually used, rather than how they are described. A jar is opened daily, often with fingers, in a room that is warm and humid for part of every day. Water and air get in. A formulation that is fine on the day it is filled has to stay fine for months of that.
The method is standardised. Known organisms are introduced at a set level, and counts are taken at intervals across the 28 day period. The formulation has to bring those counts down by set amounts by set points in time. A product that reduces contamination slowly can fail even though it eventually gets there, because the timing is part of the criteria.
This is also where a lot of appealing ideas quietly fall apart. Preservative systems are the least fashionable part of a formulation and the part most often argued with, and a system that is gentle enough to sit well on sensitive skin still has to pass the same test as any other. There is no version of this where the test is skipped because the rest of the formulation is careful.
So here is where that leaves us. The test has been done. We hold the report, from an accredited laboratory, and the product passes. We are not publishing the detail yet, because we have one open question with our manufacturer about the packaging, and we would rather answer it before we put the whole thing in front of you. When it is answered, this article gets the full result, including the parts that are less flattering.
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