What Is Oral Allergy Syndrome?

Reviewed by: HU Medical Review Board

Oral allergy syndrome (OAS) is caused by the cross-reaction of pollen allergies and related foods. These foods can include raw fruits, vegetables, some spices, and some tree nuts. OAS is also known as pollen food allergy syndrome (PFAS).1

OAS is different from a standard food allergy. However, the 2 conditions can have overlapping symptoms. Understanding what OAS is and why it happens is crucial for preventing reactions.

Symptoms of oral allergy syndrome

OAS is a type of pollen allergy in which the body reacts to specific foods that have that pollen. This is due to the similarities between the pollen on the food and the proteins in the food.1-4

Symptoms of an oral allergy include:1-4

  • Scratchy throat
  • Itchy mouth
  • Swelling of the lips, mouth, tongue, or throat

Itchy ears or hives on the mouth are sometimes reported. Usually, symptoms are focused on just the mouth and throat.1-4

It is rare to have symptoms outside of these areas or to develop anaphylaxis from OAS.1,2

The most common pollen allergies that cause OAS are birch, grass, ragweed, and mugwort. Each of these different types of pollen is linked with different foods:1-4

  • Birch
    • Apples, cherries, kiwi, peaches, pears, plums, apricots, mangos, nectarines, oranges
    • Carrots, celery, potatoes, onions, tomatoes
    • Almonds, hazelnuts, pumpkin seeds, Brazil nuts, cashews, walnuts
    • Parsley
  • Grass
    • Beans, lentils, peas, soybeans
    • Celery, tomatoes, potatoes
    • Melons, oranges, peaches, watermelon, kiwi
    • Peanuts
    • Wheat
  • Ragweed
    • Bananas, melons
    • Cucumbers, zucchini
    • Echinacea, chamomile
    • Sunflower seeds
  • Mugwort
    • Bananas, melons
    • Carrots, celery, fennel, parsnips
    • Chives, coriander, parsley
    • Peanuts

It is also possible for OAS to be triggered by a latex allergy.1-4

What causes oral allergy syndrome?

OAS occurs when people with pollen allergies develop an allergic reaction to related foods. This happens because the immune system reacts to the food’s proteins similarly to the pollen. The types of pollen listed above are related to their respective OAS foods.2,3

Sometimes, oral allergy symptoms are more common when a type of pollen is more abundant. For example, ragweed pollen counts are higher in September than in May. A person with an oral allergy to bananas may be able to eat a banana without developing a reaction in May but not in September.2

It is important to monitor your symptoms and discuss the timing of your allergies with your doctor.

Oral allergies versus food allergies

Oral allergies are allergic reactions to food. However, they are not like a standard food allergy because the reactions are caused by the immune system reacting to similar proteins found in both pollen and the food.1-4

Another difference is that people with OAS can often tolerate cooked forms of the food. For example, someone with OAS may be able to eat apple pie but not raw apples. With a food allergy, cooking does not make the body react less.1-4

The 2 conditions share the symptoms of itchiness and swelling of the mouth after eating the food.4

A person could also be allergic to only 1 type of food within a pollen group or 1 type of that food. Someone who has an oral allergy to mango may be fine eating nectarines. And someone who has an oral allergy to Granny Smith apples may be fine eating Macintosh apples.3

Oral allergies rarely cause anaphylaxis. It is possible, but it happens less often than in food allergies. However, if you have a feeling of faintness or trouble breathing, seek immediate care.1

Treatment for oral allergy syndrome

Often, oral allergies are treated by avoiding eating the food when it is raw and taking an antihistamine.3

Cooking a food or getting rid of the skin also can reduce OAS symptoms. Both of these methods either get rid of the pollen or break down the protein that causes a reaction.4

It is possible for people with OAS to have significant trouble swallowing, reactions to cooked foods, or reactions to high-risk foods like peanuts or tree nuts. If this happens, talk to your doctor about whether this is a true food allergy rather than OAS. You can also talk to your doctor about being prescribed an epinephrine auto-injector.

Many people with OAS will not need epinephrine. It is important to talk with your doctor about what is right for you.

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