An allergy to some foods, including nuts, vegetables, or fruits, is called oral allergy syndrome (OAS). Usually, people develop OAS when they have an allergy to trees, grass, or other pollens (cross-reactivity). In most cases, this type of allergy causes the lips, mouth, and throat to be itchy and rarely causes severe symptoms. Doctors often recommend avoiding the foods that trigger the symptoms of this allergy.
In other words, OAS is a type of allergy to vegetables, fruits, and nuts. In some cases, it is called pollen-food allergy syndrome (PFAS) because it results from a cross-reaction to plant pollen. Generally, an allergy occurs when the body reacts to something that the immune system thinks is harmful. In this type of allergy, the immune system makes your lips and mouth swell because it mistakes some foods for harmful substances in the body. However, the stomach acid often destroys the proteins, and the reaction does not spread.
It is quite difficult to estimate how many people have oral allergy syndrome because most of them do not report the changes they have. It mostly occurs in adults, and some research showed that about 47% to 70% of people have a pollen allergy.
Symptoms
Usually, the symptoms of OAS start quickly, right after eating trigger foods. Check below some examples:
- Tingling, itching, or minor swelling of the mouth, tongue, lips, or throat
- Bumps on the lips or mouth
- Nausea
- Hives
- Rash
- Anaphylaxis (breathing problems) and other severe reactions that occur quite rarely
- Redness or swelling of the skin when touching some raw foods
Do not hesitate to see a doctor if any of the previous symptoms occur.
Causes
Usually, this type of allergy is caused when a person eats fruits, vegetables, and nuts. Some of them contain proteins that cause the immune system to react the same way it would to a tree, grass, or plant allergen. Check below for some trigger foods:
OAS Foods List
Usually, people with an allergy to pollens develop OAS. In rare cases, people may have OAS without an allergy to pollens.
Birch Tree Pollen
- Herbs – Aniseed, caraway, coriander, fennel, parsley, and others.
- Legumes – Peanuts, soybeans, and others.
- Seed fruits – Avocados, kiwis, pears, apples, and others.
- Stone fruits – Cherries, peaches, plums, apricots, and others.
- Tree nuts – Hazelnuts, almonds, and others.
- Vegetables – Celery, carrots, and others.
Grass Pollen
These include:
- Tomatoes
- Swiss chard
- Potatoes
- Oranges
- Melons
Ragweed Pollen
- Artichokes
- Bananas
- Zucchini
- Cucumbers
Mugwort Pollen
- Garlic
- Peppers
- Mustard
- Vegetables – Cabbage, cauliflower, broccoli, parsnip, onion, and others
However, oral allergies may also include citrus fruits, figs, grapes, mangoes, pineapples, pomegranates, berries, and others.
Risk Factors
While OAS can affect anyone, some factors may increase the risk of developing it. Check below some of them:
- Pollen allergies (including birch pollen allergy and ragweed pollen allergy)
- Asthma
- Hay fever (allergic rhinitis)
- Atopic dermatitis (also known as eczema)
- Sex – According to some studies, OAS occur more commonly in women than men.
- Age – Usually, OAS occurs during adulthood.
- Family history – If you have a parent or sibling with the following health problems, your risk of developing OAS significantly increases. These include asthma, eczema, hives, and other allergies.
What Are The Potential Complications of Oral Allergy Syndrome?
People who develop OAS may also experience some complications, especially if they do not avoid the trigger foods or do not get treatment. Check below some examples:
- Exercise-induced food allergy – Some people may experience a severe reaction only when the trigger food is combined with exercise.
- Severe complications (rarely) – One of the most serious allergic reactions is anaphylaxis. It often involves trouble breathing and a sudden drop in blood pressure.
- Eosinophilic esophagitis (EoE) – This is a serious condition where immune cells build up in the esophagus, causing food allergies.
- Food protein-induced enterocolitis syndrome (FPIES)
- Nut allergies – In general, nuts can trigger OAS, but they are more likely to cause severe, systemic allergic reactions compared to vegetables and fruits.
How to Prevent Oral Allergy Syndrome?
One sure way to prevent OAS is to avoid foods that trigger it. However, physicians may also recommend some tips to prevent an allergic reaction. For example:
- Cooking the trigger foods – Sometimes, people do not have symptoms if they heat trigger fruits and vegetables. When you are preparing them, the protein changes, so it no longer causes a reaction. In most cases, people with OAS eat cooked foods, sauces, or pasteurized juices.
- Avoiding foods you are allergic to – Mostly, people with seasonal allergies have symptoms in the spring, summer, or fall. At this time, it is advised to avoid trigger foods.
- Management for existing allergies – Doctors may recommend allergy medicines because they help avoid reactions to trigger foods.
- Immunotherapy (allergy shots) – These shots contain things you are allergic to. It helps get your body used to these allergens, which reduces the risk of developing a reaction. Sometimes, immunotherapy helps people with OAS.
Diagnosis
Usually, the diagnosis of OAS begins with a physical examination to check for irregularities linked to the disease. Thereafter, doctors may ask some questions about medical history and symptoms to get more clues about the disease. However, to confirm or rule out OAS, doctors often perform the following tests. Examples include:
- Allergy skin test – During this test, doctors will scratch the skin and apply a small amount of substances that potentially cause an allergic reaction (such as tree pollen). If you develop an allergic reaction, such as a hive, it may indicate OAS.
- Food challenge test – This test involves eating increasing amounts of certain foods to see if you develop an allergic reaction.
Treatment
In general, there are no specific treatments for OAS. Usually, the allergic reactions go away on their own when you stop eating the trigger food. However, doctors may recommend some treatments for more severe allergic reactions. For example:
- Antihistamines – This group of medicines is often used to relieve the symptoms caused by an allergy. They work by blocking certain chemicals in the body. However, people who administer antihistamines still may experience mild symptoms. Doctors often recommend Diphenhydramine, Fexofenadine, and Loratadine.
- Epinephrine – This is an injection used to relieve severe symptoms caused by an allergic reaction. It helps reduce swelling of the airways and eases other symptoms. However, an Epinephrine injection is often prescribed by doctors for people with previous severe allergic reactions.
Frequently Asked Questions
Is oral allergy syndrome serious?
While most of the time, OAS is not serious, some people may develop severe allergic reactions (such as anaphylaxis). However, less than 2% of people with OAS have this severe reaction.
Does oral allergy syndrome go away?
There is no way to cure this type of allergy, but in some cases, it may go away on its own. It happens because the body gets used to the foods that once caused an allergic reaction.
When should I go to the ER?
Immediately call 911 in the U.S. or go to the nearest emergency room (ER) if any of the following symptoms occur. For example, face or tongue swelling, shortness of breath, or swallowing problems. Ask your healthcare professional if you have any other questions.
