If I remember correctly, GMCY (glyceryl caprylate) can be used at lower rates (= lowest recommended dosage) in conjunction with other preservatives if it’s meant more as a booster than a preservative. Glyceryl undecylenate is likely only working within its recommended range and I would be hesitant to reduce it too much just because you add a second/third preservative.
It also depends on things like: Are you running a stress test? Do you have issues with initial bioload or with contamination during usage? Do you know which microbes will/still grow in the simple preservation product? Do you get partial but broad spectrum preservation and only fail to reduce CFU count below your target value? Of all kinds of microbes or only certain varieties? Where do microbes grow first in/on your product?
Depending on such questions, lower amounts of aldehyde releasers may suffice to bring your blend to full speed. If you add a third preservative because of its ‘selectivity’ against a microbe insensitive to your initial blend, then the ‘full’ amount should be added. Using benzyl alcohol as a ternary might work at lower levels if its only purpose is as a headspace preservative in case of an otherwise well preserved product. That’s just to give you a few examples and ideas, not a 1:1 recommendation.
Knowing which preservative works how (if we even have a rough idea about its mode of action) and against which microbes helps to decide whether a mixture of two is redundant, partially overlapping, complementary, additive, or even synergistic (a thing maybe not very common with preservatives). And this in turn will determine if a lower % might work or most certainly won’t.
If you can’t answer those questions and run proper tests, then the use of
lower amounts, especially if you lower all used preservatives, is a
Agree re. secondary preservatives of capylyl whatever, but would not go with lesser amounts than recommended for any primary preservative (e.g. formaldehyde releasers). Please do not titirate down based on preservative testing - they are not validated to cosmetic endpoints. Please establish a system within the estabished efficacy and safety parameters for each preservative used and confrm with challenge testing. There is no advantage to lesser levels.
@Abdullah I was using it at 1% . Both myself and a colleague reacted quite severely to the Sodium Benzoate. Our skin literally went red. Neither of us had experienced an allergic reaction to anything before.
I asked around and loads of people said the same thing: they were allergic to Sodium Benzoate. So no data as such, just anecdotal.