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. Our product is going through that test now. We will not launch it until we have the result, and if the result is wrong we will start again.
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 the honest position at this point is that we do not have the result yet. Final testing is under way this autumn. If it does not come back the way it should, the work goes back a step, and the launch moves. We would rather say that now than discover we have to say it later.
STEMOVA is in pre-launch. Nothing on this site is for sale.