Chemophobia is the fear, distrust, or dislike of anything seen as "chemical." Like various other "phobias," its use is non-clinical as it is not recognised as an actual irrational fear, but rather describes a set of prejudices against chemicals.
 Which chemicals?
Since pretty much everything is a chemical (well, everything cooler than plasma) chemophobia is a somewhat odd condition. Chemophobia is specifically a distrust of what people view as "artificial" chemicals – food additives, drugs, pesticides and so on. This is usually attributed to a lack of trust and knowledge among the public, which is often fueled by tabloid-based health scares and the occasional additive shown to possibly be toxic. Advances in the field of analytical chemistry are also thought to be behind chemophobia, as modern techniques are capable of identifying substances in very low and harmless quantities.
Chemophobia has spawned many marketing campaigns designed to make the public think certain products are better. Foods or products that are advertised as "100% chemical free" – besides being nonsense because everything is a chemical – play on and reinforce fears of human-made chemicals, automatically equating them with being bad.
In particularly severe cases, chemophobia may even apply to synthetically-manufactured versions of perfectly harmless and indisputably natural (as far as that can be seriously argued to matter) chemicals like raspberry ketone.
 Appeal to nature
At the heart of chemophobia is the fallacy of "appeal to nature". This appeal makes the assumption that anything "natural" is good and anything "unnatural" is bad. As anyone with a knowledge of chemistry will know, the line between natural and unnatural chemicals is a blurred one, or even totally non-existent. Furthermore, there are many natural compounds which are very toxic (such as botulinum toxin, strychnine, lead acetate, asbestos, snake and spider venom, cardiac glycosides, cyanide, hexavalent chromium compounds...). Many industrially important chemicals are produced via natural (biological) processes, such as fermentation to produce ethanol and monosodium glutamate, or extracted from plants and bacteria, such as caffeine extracted from coffee beans. Equally, these substances can be synthesised in a lab and purified in the same way. Despite absolutely no detectable differences between purified natural products and their synthesised counterparts, chemophobia postulates that the "artificial" one is worse. (Perhaps the artificial one suffers from water memory.) Although there can be environmental or cost issues between the two production methods, this isn't always the case and is mostly irrelevant to the nature of the chemical itself.
 See also
- The Food Babe: “There is just no acceptable level of any chemical to ingest, ever”, Orac
- Sense About Science - Making Sense of Chemical Stories (pdf)
- Everything gives you cancer (well, sort of)