I try to stick to cheese pizza for this reason. We also make our own Pizza crust from brown rice flour and potato starch. And our own tomato sauce. Liz cannot tolerate wheat and gets violent throbbing headaches when she eats anything with wheat or corn syrup this includes many tomato based products. We try to stay as close as possible to a wheat free and gluten free diet.
Solid chocolate can contain artificial colorings and flavors and maybe other additives.
Check the labels. Also check what else is in the chocolate. Some soft drinks have lots of additives that might set our kids off. Fortunately, Johnny is not affected adversely by soft drinks, and does better not worse with a Mountain Dew, which is packed with sugar and caffeine. The NutriSweet really sets him off, so this is absolutely off limits for him.