Oral allergy syndrome (OAS), which is also called pollen-fruit allergy syndrome, is a type of food allergy that causes instant allergic reactions in the mouth and throat. The syndrome is caused by cross-reacting allergens found in both pollen and the protein in raw fruits, vegetables, and tree nuts.
This reaction occurs usually from eating raw or fully ripened fresh fruits and vegetables. OAS typically develops in adults with asthma and environmental allergies such as hay fever.1 When the immune system detects the pollen with similar proteins in the food, the IgE antibody in the immune system triggers an allergic reaction.2,3 Basically, the body can’t tell the difference between proteins in certain foods and pollen.
Hay fever is associated with reactions to pollens that cross-react with foods.2 Oral allergy syndrome commonly arises in adults but is rare in young children. Toddlers under three years of age have not developed the allergic rhinitis − hay fever − until they are older. It becomes more common in older children, teens, and young adults as they develop hay fever.2,3
Oral Allergy Syndrome Triggers
An allergy happens within minutes of eating the triggering food. The severity depends on the season and when certain foods are being pollinated (see Figure 1). People become most affected with oral allergy syndrome during the pollination season between April and June when allergies are at its highest. Patients then become affected again in September and October.
Symptoms may reoccur due to leaves falling and more seeds spreading. Oral allergy syndrome occurs in 50% to 70% of patients who are sensitive to birch pollen.4
The chart below shows the pollen allergy as well as the fruit, vegetable, nut, and spice that are susceptible to an allergy with that pollen. If an individual has an allergy to the pollen alder, they are more likely to have a cross-reaction to those foods listed under alder.
Allergen Cross Reactivity Pollen-Foods2-4,6
|Fruits||Peaches Pears Apples Cherries||Apples
Plums Pears Kiwis
|Peaches Oranges Melons Tomatoes||Apples
|Avocado Bananas Kiwi Papaya
|Vegetables||Celery||Celery Carrots Potatoes
Figure 1 Courtesy Lara James
Symptoms of Oral Allergy Syndrome
Symptoms are usually constrained to the mouth area and generally don’t progress beyond the mouth. The most common reaction is an itching or burning sensation in the lips, mouth, pharynx, uvula, and includes swollen or numb lips, a scratchy throat, sneezing and coughing, itching, or tingling of the tongue or roof of the mouth.
Less common reactions may affect the eyes, nose, and skin. Extreme cases are tightening of the throat such as anaphylaxis. They usually show up instantly but may take up to an hour to kick in.3
In oral allergy syndrome, anaphylaxis may occur in 2% of people. However, severe allergic reactions generally don’t happen with oral allergy syndrome. While this syndrome is concentrated to the mouth, it could progress to systemic symptoms in 9% of people.3
Oral Allergy Syndrome vs Food Allergy
An oral allergy syndrome is different than a nut allergy, which can be fatal. An episode of oral allergy syndrome recovers on its own within minutes after consuming the food. A nut allergy may last longer with severe symptoms.3 The symptoms and severity help determine the difference between an oral allergy syndrome and a food allergy.
Both types are reactions caused by specific allergy antibodies. Oral allergy syndrome lasts a few minutes and symptoms are localized in the mouth, lips, and throat region and go away without treatment. A food allergy tends to be more severe, lasts longer, usually requires some form of treatment and are associated with hives, swelling of the lips, eyelids, face, hands, trouble breathing, and/or loss of consciousness. 2
Oral Allergy Syndrome vs Latex-Food syndrome
Latex food syndrome is similar to oral allergy syndrome. Of people who are allergic to natural rubber latex, 30% to 70% have an associated hypersensitivity to some plant-derived foods (see Figure 1). In addition, an individual with an allergy to certain foods may experience allergic symptoms to latex. Cross-reactivity is the same as oral allergy syndrome with the structurally similar proteins in rubber latex and certain foods. It is caused by the IgE antibodies which cross-reactive to the antigens from the food.
Symptoms range from mild oral reactions to a severe anaphylactic reaction. They include swelling of the lips, mouth, tongue, and throat; runny nose and teary eyes; scratchy throat; itchy mouth; and redness of the mouth.6
Treatment or Management for Oral Allergy Syndrome
A few different approaches for managing this condition focus on preventing it, reversing it, or almost curing it. To prevent it, avoid the trigger foods or consume baked, canned, or frozen produce. Peel the fruits or vegetables as the protein is usually found in the skin.
Heating the food changes the chemical composition by distorting the protein which eliminates the allergen and keeps the immune system from reacting. The cooking process keeps the immune system from recognizing the food as pollen.2
If a reaction occurs, over-the-counter histamine blockers tend to work for oral allergy symptoms. Medications can be used to relieve itching, watery eyes, and scratchy throat. However, premedicating before eating these foods haven’t been proven to work.7
Immunotherapy is adding the triggers into the body to force the body in making antibodies, so it doesn’t overreact. This isn’t a full-proof cure, but it lowers the food reactions. In severe cases, an EpiPen would be needed. In the small percentage of people who have severe symptoms that progress beyond the mouth, medical attention should be sought.3,7 While getting a skin test will help determine the food allergy, injections for pollen allergies may help with symptoms.2
Oral allergy syndrome may be confusing to people. With a skin prick test, they will test negative for food allergies and positive for the variety of pollens. Many people with pollen allergies may be aware they can’t tolerate certain foods and may think they have a true food allergy and never make the connection that it may just come down to something as simple as their hay fever.
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- Oral Allergy Syndrome (OAS). Children’s Hospital of Philadelphia. Retrieved from https://www.chop.edu/conditions-diseases/oral-allergy-syndrome-oas.
- Pollen Food Allergy Syndrome. American College of Allergy, Asthma, & Immunology. Retrieved from https://acaai.org/allergies/types/food-allergies/types-food-allergy/oral-allergy-syndrome.
- What is Oral Allergy Syndrome? Healthline. Retrieved from https://www.healthline.com/health/oral-allergy-syndrome#triggers-of-oas.
- Sussman, G., Sussman, A., Sussman, D. Oral allergy syndrome. CMAJ. 2010; 182(11): 1210-1211. doi:10.1503/cmaj.090314.
- Wagner, S., Breiteneder, H. The latex-fruit syndrome. Biochem Soc Trans. 2002; 30(Pt 6): 935-940. doi:10.1042/bst0300935.
- Kerkar, P. Latex Food Syndrome: Symptoms, Treatment, Common Foods Related to Latex Food Syndrome. Retrieved from https://www.epainassist.com/allergies/latex-food-syndrome.
- Tourangeau, L.M., Walford, H.H., Nguyen, J.T. Oral Allergy Syndrome (OAS). Stanford Health Care Stanford Medicine.