Food allergy

DEFINITION

Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives or swollen airways. In some people, a food allergy can cause severe symptoms or even a life-threatening reaction known as anaphylaxis.

Food allergy affects an estimated 6 to 8 percent of children under age 3 and up to 3 percent of adults. While there’s no cure, some children outgrow their food allergy as they get older.

It’s easy to confuse a food allergy with a much more common reaction known as food intolerance. While bothersome, food intolerance is a less serious condition that does not involve the immune system.

CAUSES

When you have a food allergy, your immune system mistakenly identifies a specific food or a substance in food as something harmful. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE) antibodies to neutralize 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 allergy 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
• Peanuts
• Tree nuts, such as walnuts and pecans
• Fish
• Eggs

In children, food allergies are commonly triggered by proteins in:

• Eggs
• Milk
• Peanuts
• Tree nuts
• Wheat

Food intolerance and other reactions

There are a number of reactions to food that cause similar symptoms to a food allergy. 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 may 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, reduce your ability to digest lactose, the main sugar in milk products. Lactose intolerance can cause bloating, cramping, diarrhea and excess gas.
• Food poisoning. Sometimes food poisoning can mimic an allergic reaction. 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 severe reactions include monosodium glutamate (MSG), artificial sweeteners and food colorings.
• Histamine toxicity. Certain fish, such as tuna or mackerel, that are not refrigerated properly and that contain high amounts of bacteria may contain high levels of histamine that trigger symptoms similar to those of food allergy. Rather than an allergic reaction, this is known as histamine toxicity or scombroid poisoning.

• 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, leading to an inability to absorb certain nutrients.

SYMPTOMS

For some people, an allergic reaction to a particular food may be uncomfortable but not severe. For other people, an allergic food reaction can be frightening and even life-threatening. Food allergy symptoms usually develop within a few minutes to two hours after eating the offending food.

The most common food allergy signs and symptoms include:

• Tingling or itching in the mouth
• Hives, itching or eczema
• Swelling of the lips, face, tongue and throat or other parts of the body
• Wheezing, nasal congestion or trouble breathing
• Abdominal pain, diarrhea, nausea or vomiting
• Dizziness, lightheadedness or fainting

Anaphylaxis

In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening signs and symptoms, including:

• Constriction and tightening of airways
• A swollen throat or the sensation of a lump in your throat that makes it difficult to breathe
• Shock with a severe drop in blood pressure
• Rapid pulse
• Dizziness, lightheadedness or loss of consciousness

Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or even death.

Exercise-induced food allergy

Some people have an allergic reaction to a food triggered by exercise. Eating certain foods may cause you to feel itchy and lightheaded soon after you start exercising. In serious cases, an exercise-induced food allergy can cause certain reactions such as hives or anaphylaxis.

Not eating for a couple of hours before exercising and avoiding certain foods may help prevent this problem.

Pollen-food allergy syndrome

In many people who have hay fever, fresh fruits and vegetables and certain nuts and spices can trigger an allergic reaction that causes the mouth to tingle or itch. In some people, pollen-food allergy syndrome — sometimes called oral allergy syndrome — can cause swelling of the throat or even anaphylaxis.

This is an example of cross-reactivity. Proteins in fruits and vegetables cause the reaction because they’re similar to those allergy-causing proteins found in certain pollens. For example, if you’re allergic to ragweed, you may also react to melons; if you’re allergic to birch pollen, you may also react to apples.

Cooking fruits and vegetables can help you avoid this reaction. Most cooked fruits and vegetables generally don’t cause cross-reactive oral allergy symptoms.

Common cross-reactivity between pollens and fruits and vegetables:

When to see a doctor

See a doctor or allergist if you have food allergy symptoms shortly after eating. If possible, see your doctor when the allergic reaction is occurring. This will help your doctor make a diagnosis.

Seek emergency treatment if you develop any signs or symptoms of anaphylaxis, such as:

• Constriction of airways that makes it difficult to breathe
• Shock with a severe drop in blood pressure
• Rapid pulse
• Dizziness or lightheadedness