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glycerol to preserve cosmetics
How much glycerol should be added to a product to notice a decrease of the water activity?
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3 Replies
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It doesn’t matter. If you read about Water Activity (Aw), one of the stated rules is that Aw must be measured and it should never be extrapolated. As such, you can use glycols to boost a preservative system, but it is highly unlikely that without very specific testing during the Formulation as week as a QC test during Production that you could ever use it as a sole preservative.
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it is actually related to %w/w of water, but it’s not a linear relationship, or in a multi-component system, an easily calculable one: with a water/glycerine mixture, you’d need at least 40% w/w of glycerine before any significant inhibition of microbial growth occurs
in cosmetics, this is only useful in things like toothpastes, which generally have than 50% w/w water
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Should never be used as single preservative in any product absorbs water and promotes growth.
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