What are food allergies and oral allergy syndrome?

A food allergy is an abnormal response to a food triggered by the body’s immune system. In adults, the foods that most often trigger allergic reactions include fish, shellfish, peanuts and tree nuts, such as walnuts. Problem foods for children can include eggs, milk, peanuts, tree nuts, soy and wheat.

Oral allergy syndrome is also called food pollen syndrome. The body of a person allergic to a specific pollen is fooled into thinking that the pollen is present in some foods, and reacts to the food with local tingling and itching where the food has come into contact.

There are two types of true food allergies:

  • A typical true immediate food allergy is one such as peanuts or shrimp. A reaction occurs immediately after eating the food, or eating something contaminated with a tiny or invisible amount of the offending food. Immediate reactions can be severe or life-threatening.
  • The second type of food allergy has symptoms that usually develop over several hours after eating the food. The severity of the symptoms may be related to how much of the food is eaten: a person may tolerate a small amount of a particular food without having problems, but will develop symptoms if more is eaten.

The other broad category of reactions to foods is food intolerance. These are reactions aren’t true allergies because they aren’t caused by the immune system at all. They may be enzyme deficiencies, the direct effects of the food on histamine or even food poisoning. For example, you may know someone who is lactose intolerant. This isn’t a true allergy, but rather a deficiency of the enzyme needed to digest the proteins in milk. Sometimes lactose intolerant people can tolerate other dairy products, like cheese or yogurt.

What causes food allergies and oral allergy syndrome?

There are some foods that contain a naturally occurring chemical similar to the body’s main chemical messenger of allergy, histamine. There are also chemicals in foods that can cause the body to release histamine directly without any participation by the immune system. These can cause symptoms in very sensitive individuals. Foods that may do this include strawberries and tomatoes.

Oral allergies are caused when there’s a cross reactivity between pollens and foods. Often there may be a protein in a certain kind of food that’s very similar to a protein in a certain pollen. When the allergic person eats that food, the body reacts as if the pollen is present in the food.

Common cross-reacting foods include melons that can trigger ragweed symptoms, or bananas, avocados and chestnuts, which can cause a reaction in someone who’s allergic to latex.

What are the symptoms of food allergies and oral allergy syndrome?

 Some typical symptoms of food allergy include:

  • Itching or swelling in your mouth
  • Vomiting, diarrhea, or abdominal cramps and pain
  • Hives or eczema
  • Tightening of the throat and trouble breathing
  • Drop in blood pressure

The symptoms of oral allergy syndrome include tingling or itching of the lips, tongue, cheeks, roof of the mouth and throat after eating certain foods. Swelling of these areas may occur, too, on rare occasions.

In some cases, difficulty swallowing could be a sign of a condition known as eosinophilic esophagitis. This allergic reaction is triggered by food and environmental allergens and causes white blood cells in the throat to become inflamed.

How does Ohio State diagnose food allergies and oral allergy syndrome?

Your Ohio State University Wexner Medical Center physician may take a detailed history, and order skin and blood tests to diagnose a food allergy. Sometimes a person’s history makes it clear that a particular food is responsible. If not, a blood test checking for specific foods may be used to guide the diagnosis.

Skin testing, done for inhalant or environmental allergens, may suggest a food allergy. A skin test that is negative is pretty reliable in saying that person is not allergic to that food, but a positive skin test doesn’t necessarily mean that food is causing clinical symptoms.

How does Ohio State treat food allergies and oral allergy syndrome?

You can only prevent the symptoms of food allergy or oral allergy by avoiding the food. After you and your physician have identified the foods that cause you problems, you must remove them from your diet.

The current treatment of immediate-type food allergies is lifelong avoidance. Avoiding obvious forms of the food is pretty easy. For example, if you’re allergic to milk you won’t drink it. But whey is a milk protein, and is found in many prepared foods such as bread.

Another concern is the risk of accidental exposure: the restaurant waiter who doesn’t take seriously your request for “nothing containing shrimp,” or the classmate who brings cookies to your child’s classroom, forgetting that the treats contain peanuts.

A mild food-allergy reaction can be treated with an over-the-counter oral antihistamine. More severe reactions, such as trouble breathing, lip and tongue swelling or a feeling like your throat is closing, may require an injection of epinephrine (adrenaline).

When you have severe food allergies, you must be prepared to treat an accidental exposure. Wear a medical alert bracelet or necklace, and carry an auto-injector device containing epinephrine.

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