I am聽no alarmist when it comes to "artificial chemicals" used in food or cosmetic production. But I do question the use of colourants because they have no function other than changing the appearance of a product. Why do we need mouthwash to be blue? It's because somehow people have been conditioned to associate blue with cleanliness, which is why window cleaners, toilet bowl cleaners and mouthwashes are blue.
The colourant most commonly used is "Brilliant blue #1," not one of the synthetic dyes that was associated with hyperactivity in children in the famous University of Southampton study that implicated six colours and started the scampering to replace synthetic colours with natural ones. Brilliant blue can in rare cases cause allergies, but that is true for almost any substance, natural or synthetic, with which we come into contact.
Colours isolated from natural sources, such as betanin from beetroot or carmine from the cochineal beetle undergo the same stringent approval process as do synthetic colours, but testing for hyperactivity is not one of the criteria. Industry prefers synthetic colours because in general they are less susceptible to changes in pH and are more stable when it comes to exposure to light or oxygen. Although allergic reactions to colours are rare and the hyperactivity connection is certainly not iron-clad, why not educate people not to expect brilliantly coloured products?
The industry would probably argue that in the case of mouthwash, if it were colourless, people would think they are being duped into buying water. That brings up the question of why we need mouthwash in the first place. But that's another story for another time. Just one more thing...replacing Brilliant blue #1 in blue Smarties by phycocyanin isolated from blue-green algae does not make them smarter to eat.
