Oral allergy syndrome (OAS) is a common food-related allergy that develops in adults. OAS is connected to environmental allergies, such as hay fever.

When you have oral allergy syndrome, certain fresh fruits, nuts, and vegetables can trigger an allergic reaction because of proteins with a similar structure to pollen.

In other words, your body confuses a fruit protein with a pollen. The IgE antibody in your immune system produces an allergic reaction.

For this reason, the condition is sometimes called pollen-fruit allergy syndrome. The symptoms tend to be worse during times of the year when pollen levels are high.

Different people are triggered by different foods. However, OAS only happens as the result of cross-reactivity between pollen and similarly structured proteins in certain fruits.

Some common triggers of OAS include:

  • bananas
  • cherries
  • oranges
  • apples
  • peaches
  • tomatoes
  • cucumbers
  • zucchinis
  • bell peppers
  • sunflower seeds
  • carrots
  • fresh herbs, such as parsley or cilantro

If you have OAS, tree nuts, such as hazelnuts and almonds, can cause an allergic reaction. Oral allergy syndrome is different from other nut allergies that can prove fatal.

People with oral allergy syndrome generally won’t have a severe allergic reaction. However, anaphylaxis can occur in almost 2 percent of people. The reaction is usually limited to the area of the mouth but can progress to systemic symptoms in up to 9 percent of people.

OAS symptoms can vary, but they tend to be concentrated in the area of the mouth. They rarely affect other areas of the body. When your OAS is triggered, you may have these symptoms:

  • an itching or tingling on your tongue or the roof of your mouth
  • swollen or numb lips
  • a scratchy throat
  • sneezing and nasal congestion

The best treatment for OAS is straightforward: Avoid your trigger foods.

Some other easy ways to reduce OAS symptoms include these tips:

  • Cook or heat your food. Preparing food with heat changes the chemical composition. Many times, it eliminates the allergen.
  • Buy canned vegetables or fruits.
  • Peel vegetables or fruits. The OAS-causing protein is often found in the skin of the produce.

Over-the-counter (OTC) treatments

OTC histamine blockers, or antihistamines, used for hay fever may work for oral allergy symptoms, according to one study.

Diphenhydramine (Benadryl) and fexofenadine (Allegra) can be used to relieve the itching, watery eyes, and scratchy throat that come along with high-pollen days when you have allergies. They can sometimes suppress OAS reactions as well.

Pre-medicating with antihistamines before eating these foods has not been shown to be completely effective.

Immunotherapy

People who were treated with immunotherapy for OAS have had mixed reactions. In one clinical study, participants could tolerate small amounts of the birch pollen triggers after immunotherapy. However, they couldn’t overcome OAS symptoms completely.

Because the symptoms of oral allergy syndrome are not dangerous, ask your doctor if you can try different potential OAS triggers to see what you react to.

People who have allergies to birch pollen, grass pollen, and ragweed pollen are most likely to have OAS, according to the American College of Allergy, Asthma, and Immunology.

Young children are not usually affected by oral allergy syndrome. Often, young adults will have symptoms of OAS for the first time after having eaten trigger foods for years without a problem.

The pollination season — between April and June — tends to be the peak time for OAS. Sometimes September and October will bring on symptoms again since trees lose their leaves and plenty of seeds are available.

In 9 percent of people with oral allergy syndrome, symptoms can become more severe and require medical assistance. If you have a reaction to a pollen-based food that extends beyond the area of the mouth, you should seek medical attention.

In some very rare cases, OAS can trigger anaphylaxis. In other cases, people may confuse their serious nut or legume allergies with oral allergy syndrome.

Make sure you speak to your doctor about the intensity and severity of your symptoms. You might need to be referred to an allergist to be certain that your symptoms are caused by OAS.