Allergies are the result of an immune system mistake. Sometimes your body thinks a harmless substance is dangerous, and in response it launches an attack. When it comes to food dyes, some actually are harmful, but not in the way your immune system thinks they are. Food dye allergies can affect children and adults, but they're rare in both cases. The ones most likely to cause a problem are Yellow 5, Yellow 6, Blue 1 and Red 40. Plus, natural reds that come from carmine, cochineal and Annatto can cause allergic reactions, too. Although such allergies are highly unlikely, the potential reaction of anaphylaxis makes them dangerous to some people.
Beyond allergy risks, though, food dyes are harmful for their carcinogenic properties. Red 3, Red 40, Blue 1, Blue 2, Green 3, Yellow 5 and Yellow 6 all have been linked to cancer. And according to studies, some of the food dyes cause hyperactivity in children.