In a true food allergy, your immune system mistakenly identifies a specific food or a substance in food as a harmful substance. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE) antibodies to fight the culprit food or food substance (the allergen). The next time you eat even the smallest amount of that food, the IgE antibodies sense it and signal your immune system to release a chemical called histamine, as well as other chemicals, into your bloodstream.
These chemicals cause a range of allergic signs and symptoms. They are responsible for causing allergic responses that include dripping nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing, and even anaphylactic shock.
The majority of food allergies are triggered by certain proteins in:
- Shellfish, such as shrimp, lobster and crab
- Tree nuts, such as walnuts and pecans
In children, food allergies are also commonly triggered by proteins in:
- Tree nuts
Chocolate, long thought by some parents to cause food allergies in children, rarely triggers a food allergy.
Food intolerance and other reactions
There are a number of reactions to food that cause similar symptoms to a food allergy. If you have digestive symptoms, chances are it’s not a true food allergy, but a food intolerance. Depending on the type of food intolerance you have, you may be able to eat small amounts of problem foods without a reaction. By contrast, if you have a true food allergy, even a tiny amount of food may trigger an allergic reaction. Because a food intolerance may involve some of the same signs and symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea — people often confuse the two.
One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself but to a substance or ingredient used in the preparation of the food.
Common conditions that can cause symptoms mistaken for a food allergy include:
- Absence of an enzyme needed to fully digest a food. You may not have adequate amounts of some enzymes needed to digest certain foods. Insufficient quantities of the enzyme lactase, for example, reduces your ability to digest lactose, the main sugar in milk products. Lactose intolerance can cause bloating, cramping, diarrhea and excess gas.
- Irritable bowel syndrome. Certain foods may trigger the signs and symptoms of irritable bowel syndrome. You may find that certain foods will cause cramping, constipation or diarrhea. Steer clear of these foods to avoid the symptoms.
- Food poisoning. Sometimes food poisoning can mimic an allergic reaction. Some types of mushrooms and rhubarb can be toxic. Bacteria in spoiled tuna and other fish also can make a toxin that triggers harmful reactions.
- Sensitivity to food additives. Some people have digestive reactions and other symptoms after eating certain food additives. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people. Other food additives that could trigger bad reactions include monosodium glutamate (MSG), artificial sweeteners and food colorings.
- Recurring stress or psychological factors. Sometimes the mere thought of a food may make you sick. The reason is not fully understood.
- Celiac disease. While celiac disease is sometimes referred to as a gluten allergy, it isn’t a true food allergy. Like a food allergy, it does involve an immune system response, but it’s a unique immune system reaction that’s more complex than a simple food allergy. This chronic digestive condition is triggered by eating gluten, a protein found in bread, pasta, cookies, and many other foods containing wheat, barley or rye. If you have celiac disease and eat foods containing gluten, an immune reaction occurs that causes damage to the surface of your small intestine and an inability to absorb certain nutrients. Symptoms of celiac disease include diarrhea, abdominal pain and bloating. In some cases, celiac disease causes malnutrition and nutrient deficiencies.