Many people have a food intolerance. This term refers to heartburn, cramps, belly pain, or diarrhea that can occur after they eat foods such as:
- Corn products
- Cow's milk and dairy products (lactose intolerance)
- Wheat and other grains that contain gluten (celiac disease)
A true food allergy is much less common.
The immune system normally protects the body against harmful substances, such as bacteria and viruses. It also reacts to foreign substances called allergens. These are usually harmless and in most people do not cause a problem.
In a person with a food allergy, the immune response is oversensitive. When it recognizes an allergen, the immune system launches a response. Chemicals such as histamines are released. These chemicals cause allergy symptoms.
Any food can cause an allergic reaction. The most common food allergies are to:
- Eggs (mostly in children)
- Fish (older children and adults)
- Milk (people of all ages)
- Peanuts (people of all ages)
- Shellfish such as shrimp, crab, and lobster (people of all ages)
- Soy (mostly in children)
- Tree nuts (people of all ages)
- Wheat (people of all ages)
In rare cases, food additives, such as dyes, thickeners, and preservatives, can cause a food allergy or intolerance reaction.
Some people have an oral allergy. This is an allergy type syndrome that affects the mouth and tongue after they eat certain fresh fruits and vegetables:
- Melons, apples, pineapple, and other foods contain substances that are similar to certain pollens.
- The reaction most often occurs when you eat the raw form of the foods. How severe the reaction is depends on how much of the food you eat.