It is not unusual to hear about people reacting to certain food additives. We all have friends or colleagues who react to too much caffeine or salt. Others react to dyes and preservatives in foods.
These are not allergies per se, but could be deemed intolerances. In fact, it is difficult to ascertain who will get hyper from too much caffeine and who will drink twelve cups a day and sleep like a baby.
Apart from these rather obvious reactions, there are more subtle responses to additives. Symptoms are sometimes so subtle that they go unnoticed, and unless someone is really looking for the causes of a repetitive condition or symptoms, they may go unnoticed for decades.