Allergic reactions to food can be mild or severe. If you have a food allergy, even a little bit of that food is dangerous. In Canada, food labels on any packaged food MUST show if that food contains any of 10 common allergens: milk, eggs, peanuts, mustard, seafood, sesame, soy, sulphites, tree nuts, and wheat.
Food intolerances are not as serious as allergies. With a food allergy, a tiny bit of food causes symptoms. With a food intolerance, a tiny bit usually has no effect.
Some people suffer digestive problems when they eat certain foods. The most common foods that cause this are dairy products, grains with gluten (such as wheat), and foods that cause gas such as beans and cabbage.