Question: When my child eats citrus fruits or tomato, he/she gets a red, non-raised rash around the mouth. Does this mean he is allergic to these foods?
Answer: He's most likely not allergic to these foods. There are food reactions that are more related to the irritant properties of the food rather than an allergic reaction.
And with an allergic reaction, we're really talking about the immune system causing those symptoms, whereas with this type of reaction, it's much more likely that the irritant properties of those foods -- and citrus and tomato would be two really good examples of when these kinds of reactions happen -- that cause this localized rash, just because that acid in the food is irritating to the localized area where it may come in contact.
So if the irritation is too severe, we might need to restrict those foods. But if it's mild and goes away on its own, those are not even necessarily foods that would need to be restricted from your son's diet.