Take milk. For people with milk allergies, a splash in their cereal can trigger an immune response that results in hives, itchy skin, and, yes, even anaphylaxis. More common, however, is lactose intolerance. A splash of milk in the cereal of a lactose intolerant may result in cramps, constipation, or diarrhea, but that's about it. The difference is that for people with milk allergies, milk triggers the production of histamines, while people with lactose intolerance just aren't producing enough lactase enzymes to break up the lactose in milk once it hits their hungry tummies. And many food intolerances, while a legitimate source of digestive woes, may not yet have a clear biological source, like my own allium intolerance, which makes garlic, onion, and their ilk an intestinal menace.