Hi,
I am trying to find information about the required number of volunteers for a 48h patch test in the US. This test will be conducted for a US cosmetic product launch. I was surprised to learn that in Europe 10 volunteers can be enough.
What would you generally recommend?
Thanks,
Elsa
Assuming that you are not introducing a cosmetic product containing new, before never used substances, a patch test in such cases is regarded as a compatibility test. It is intended to confirm that there are no harmful effects when applying a cosmetic product to the human skin or mucous membrane, as already expected from other sources. So, patch testing in these circumstances is not in the first place an allergenicity test, because for that purpose you would need at least several hundreds of volunteers. That is also the reason why it is impossible to prescribe a certain number of volunteers. Ten is really the minimum. In my experience twenty is a quite suitable number.
It is wrong to say in Europe is accepted, the choice of number of volunteeers is related to many aspects: goal of the test (as said may be only confirmation), representative statistic of population, type of product, application, laboratory experience and standardization.
As safety assessor I do not accept tests with less then 18 (better 24) volunteers correctly randomized, be aware that if the test is not sgnificant, authorities may question it and consider the safety assessment as not valid.
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