I have often seen concern expressed over the sheer number of (synthetic) chemicals used in cosmetics, and over the number of chemicals detected in human breast milk, urine etc. These numbers are then often used to concoct a scare over the potential for a “cocktail effect”, i.e. a mythical series of interactions between these substances that then produces unexpected adverse health effects. I use the term “mythical” because there is no actual proof that such an effect exists; certainly not in the manner suggested. Sense About Science – page 9.
It is notable that this claim is only ever made with respect to synthetic substances. However, let’s consider natural substances instead. To use a very simple example, an apple is natural, and contains hundreds of different substances. Aloe vera is natural and, similarly, contains hundreds of different substances. But how natural is it to put extracts of these plants together on human skin? The hundreds/thousands of different substances contained within extracts of those two plants would never be found in such intimate proximity in nature, so placing them on the skin is no longer reflecting a natural state of affairs. This is just an example, but it may be extrapolated to any almost combination of plant extracts – they would simply never be found mixed together in nature. This opens up the possibility of chemical interactions that are never likely to occur within the plant in its native state. None of these interactions are ever studied (an accusation frequently thrown at synthetic substances), so how do we know that such combinations are safe for use in cosmetics? The safety of the vast majority of the components of natural extracts is not fully established (but frequently assumed – see the Skin Deep database for ample evidence of such assumptions), so how do we know that we are not at risk when using combinations of natural substances in unnatural combinations?
Both benzoic acid and ascorbic acid (vitamin C) exist in nature but, when used in combination, benzene can be produced (this actually happened in Coca Cola – with sodium benzoate, which was replaced very quickly!)
I appreciate that I have stated that the “cocktail effect” does not really exist, so my argument over such an effect with natural materials is very weak, but my point here is that those who DO claim such an effect for synthetics should, logically, accept that the possibility exists for the same effect with natural substances. So, either accept that it doesn’t exist to any significant extent for synthetic substances, or exercise more caution and call for more testing of natural substances – you can’t have it both ways!