Our oldest son reacts to Vanillin.  His reactions are behavioural. He stops listening or following instruction and becomes disagreeable. We also see really distinct rough behaviour towards his younger brother. We usually notice a reaction the next day and it lasts for quite a while compared to his other reactions. After Marshmallows it lasted a week!  It also doesn't seem to take a very high dose to start the reactions. For us it is an absolute avoid-at-all-costs additive, we never compromise on this as we do with other things. It is simply not worth it.

I've heard so much conflicting info about this additive, so many people seem to think it isn't a bad additive. Sadly, I must disagree – Ruth, by email.