What else besides food allergies can cause reactions to foods?

One possible culprit is food poisoning. If other people also got sick after eating the offending food, it usually means that contaminated food is to blame.

It's also easy to confuse a food allergy with another abnormal reaction to food—a food intolerance. Both conditions share some of the same symptoms, including nausea, diarrhea, and stomach cramps.

Food intolerances are fairly common. For example, many people have lactose intolerance, or trouble digesting the sugar that's in milk and most dairy products. When they drink milk, they have gas, bloating, cramps, and sometimes diarrhea.

Other people feel sick if they eat foods with histamine, a natural substance found in cheese, some wine, and certain types of fish. Some food additives, including dyes, sulfites, and monosodium glutamate (MSG), also can trigger reactions in some people.

What's the difference between food intolerances and food allergies? Unlike allergies, intolerances are not triggered by the immune system.

The causes of intolerances vary. For instance, people with lactose intolerance have low amounts of the enzyme lactase, which is needed to digest dairy products. In some cases, food intolerances stem from unpleasant memories associated with a food.

Sometimes it takes some sleuthing to determine whether you have a food allergy, as well as what food is causing your symptoms.