What is Oral Allergy Syndrome (OAS)?
Oral allergy syndrome (OAS) is a type of allergy to certain raw fruits, vegetables and nuts. Symptoms primarily affect the mouth, lips and throat. OAS is also known as pollen-food allergy syndrome (PFAS).
Oral allergy syndrome occurs when people with tree, grass or ragweed pollen allergies have symptoms after eating raw fruits, vegetables or nuts. These are foods with proteins that are very similar to pollen proteins. Because of this, the body gets confused and reacts as if the food is pollen.
OAS symptoms are usually mild: an itchy mouth or sore throat. But allergic symptoms can be worse during pollen season, when there’s more pollen in the air.
How is OAS different from a true food allergy?
OAS is caused by immunoglobulin E (IgE) antibodies in the body. These are special defenders that help the body protect itself from harmful germs and bacteria. The IgE antibodies help fight off the germs and bacteria.
In people with OAS, the body makes IgE antibodies to pollen that comes from trees, grasses and weeds. Certain raw fruits, vegetables and nuts have proteins that are similar to pollen proteins. When you eat one of these foods, you develop OAS symptoms because your immune system is confused. It reacts to the food, even though you’re not truly allergic to the food itself.
In a true food allergy, the body makes IgE antibodies to the food or food protein. This means even a small amount of food can cause a serious allergic reaction at any time.
| Oral Allergy Syndrome (OAS) | IgE-Mediated Food Allergy |
|---|---|
| Reaction caused by IgE antibodies to pollen | Reaction caused by IgE antibodies to the food or food proteins |
| Raw fruits/veggies look like pollen proteins | The food itself triggers the reaction |
| Symptoms are mild and in the mouth/throat | Symptoms can be severe and affect the whole body. Can cause anaphylaxis |
| Reactions happen mostly during pollen season | Reactions can happen any time you are exposed to the food |
| If the food is cooked, fewer or no symptoms | Cooking does not make food safe |
People diagnosed with allergic rhinitis (also called hay fever) are more likely to experience OAS. It’s important to note that although OAS usually causes mild symptoms, severe reactions can occur in rare cases.
Examples of OAS include:
- Irritated gums or swollen lips after eating raw foods, like a fruit or vegetable
- A runny nose or itchy eyes from ragweed pollen proteins (this is a pollen allergy reaction)
- An itchy, tingly mouth, swollen lips and/or a sore throat after eating certain raw fruits or vegetables
What causes oral allergy syndrome?
OAS is caused by what’s called cross-reactivity. This happens when your immune system mistakes certain proteins in raw fruits, vegetables or nuts for the proteins found in pollens. The proteins in these foods are like pollen proteins. Your body reacts to the food as if it were pollen.
Here’s how it works:
- Your body is allergic to a protein in pollen.
- You eat a raw food with similar pollen proteins.
- Your immune system is unable to tell the difference.
- It thinks the food is dangerous and releases IgE antibodies to try to fight it.
- Your body reacts and causes allergy symptoms like an itchy mouth or swollen lips.
This usually only happens with raw foods, not cooked foods. Symptoms are more common during pollen season.
For example, if you’re allergic to birch pollen and eat a raw apple, your body might react because the apple protein looks like birch pollen.
How common is oral allergy syndrome?
As many as 1 out of every 3 people diagnosed with seasonal allergies may experience oral allergy syndrome. However, the condition often goes undiagnosed because the symptoms are usually mild.
OAS usually doesn’t occur in young children. It tends to start in older children, teens, or adults. People can eat the foods for years without a problem, and only react after developing a pollen allergy.
What pollens commonly trigger OAS symptoms?
Pollens that commonly trigger OAS symptoms are usually:
- Birch tree pollen
- Grass pollen
- Ragweed pollen
- Mugwort pollen (a weed pollen)
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What foods cause oral allergy syndrome?
The lists below show foods that are related to certain pollens. These foods may have similar proteins that trigger OAS symptoms.
| Pollen Type | Fruits | Vegetables | Nuts / Legumes | Herbs / Spides |
|---|---|---|---|---|
| Alder | Apple, cherry, peach, pear, raspberry, strawberry | Celery, carrot | Almond, hazelnut | Parsley |
| Birch | Apple, apricot, cherry, kiwi, mango, lychee, parsnip, peach, pear, plum, nectarine | Carrot, celery, potato | Almond, hazelnut, peanut, soy | Parsley, fennel, coriander |
| Chenopod (Goosefoot) | Melon, banana | Swiss chard, beetroot, spinach | ||
| Grass (e.g., Timothy, Orchard) | Melon, orange, watermelon, kiwi, peach, apricot, plum | Tomato, white potato, celery, carrot, green pea | Peanut | |
| Mugwort | None specific | Celery, carrot, bell pepper, garlic, onion, broccoli, cauliflower, spinach, beetroot | Sunflower seed | Coriander, fennel, parsley, paprika, aniseed, mustard, chamomile tea |
| Olive Tree | Tomato, melon, kiwi, apple, fig | |||
| Plane Tree | Peach, apple, cherry | None specific | Hazelnut, peanut, pistachio | |
| Ragweed | Banana, cantaloupe, honeydew, watermelon | Cucumber, zucchini, artichoke, romaine lettuce, endive | Sunflower seed | Chamomile, echinacea, dandelion, hibiscus, honey (in rare cases) |
Note: This is not a full list. These foods usually cause symptoms only when eaten raw. Cooking them can change the structure of the proteins so that they don’t cause a reaction.
Latex-fruit syndrome
People with latex allergy may have a similar reaction to some fruits. Latex-fruit syndrome is also caused by IgE antibodies. Cross-reactive foods with latex include banana, avocado, kiwi, chestnut, tomato, papaya, passionfruit, fig, peach, plum, melon and potato.
What are the symptoms of oral allergy syndrome?
OAS symptoms usually affect the mouth and nearby areas. They don’t usually affect other parts of the body, like the stomach or lungs. Common symptoms include:
- Itchy mouth or tingling sensation
- Significant throat discomfort
- Swelling of the lips, mouth, tongue, or throat
- Hives on the lips or inside the mouth
Most OAS symptoms are mild. Get medical help right away if you have significant swelling in the mouth, tongue or throat.
Some may experience systemic reaction symptoms like:
- Upset stomach
- Skin reactions beyond the lips or mouth
- In rare cases, anaphylaxis (a severe allergic reaction)
If you have trouble breathing, have vomiting or diarrhea, feel faint, and/or your symptoms spread beyond the mouth, this may be anaphylaxis. Seek medical help immediately.
When do pollen food allergy syndrome symptoms happen?
Symptoms can appear suddenly, even after years of eating the same fruits or vegetables without issue. OAS reactions generally only happen with raw fruits, vegetables and some tree nuts. The symptoms often appear within minutes and go away in about 30 minutes.
Reactions may feel random because they are not the same throughout the year. These reactions happen mostly during pollen season. That’s when your immune system is already reacting to pollen in the air.
You might eat fruit with no problems one month and then have symptoms the next. For example, people allergic to ragweed pollen may tolerate melon in February because that is when the fruit is dormant. But they may react to it in September, when ragweed pollen is more common.
Does cooking OAS foods reduce or stop symptoms?
Yes. Cooking, baking or microwaving fruits and vegetables can reduce or even stop OAS symptoms. Heat changes the shape of the proteins in food. When the shape of protein changes, the immune system may not react to it.
But this doesn’t work for everyone. Some foods contain stronger proteins, like lipid transfer proteins (LTPs) and storage proteins. These are heat-stable, which means they don’t break down easily during cooking. So even after the food is heated, these proteins may still cause a reaction.
For example:
- Peach and cherry skins contain LTPs.
- Hazelnuts and peanuts contain storage proteins.
If someone has a reaction to these foods even when they’re cooked, they may react to these tougher proteins, not just OAS.
Here are a few ways you can stop or limit your reaction:
- Cook, bake, or microwave the food. Heating often alters protein structure. For example, someone may react to raw apples but tolerate them in apple pie.
- Peel the skin off fruits and vegetables. Many allergenic proteins are concentrated in the skin. Peeling can reduce exposure. You could even try microwaving an apple to see if that helps.
- Use canned or jarred versions. Processed versions (like canned peaches or tomato paste) have often been heat-treated and may be tolerated.
- Try alternative varieties. Try different varieties of the same fruit (e.g., Granny Smith vs. Fuji apples).
Not everyone will tolerate cooked or peeled versions. Some people may still react while preparing or touching raw foods.
How is oral allergy syndrome diagnosed?
Most OAS symptoms go away when you stop eating the food. It’s a good idea to see an allergist anytime you experience allergy symptoms related to food. Symptoms can sometimes alert you to other allergies, such as allergies to food or latex. A diagnosis will also help you pinpoint which pollens you are allergic to and can help you better manage pollen allergies throughout the year.
The allergist will determine whether your symptoms are a mild cross-reaction or whether they could lead to a life-threatening allergic reaction such as anaphylaxis. Anaphylaxis from oral allergy syndrome is extremely rare. If you’re at risk for anaphylaxis, you may require a prescription for epinephrine, the first-line treatment.
An evaluation by a board-certified allergist is recommended. Doctors use a few tools to figure out if you have OAS:
- Medical history. Your doctor will ask questions about your symptoms and when they happen.
- Skin prick test for pollen. A small amount of pollen is placed on your skin, then the skin is gently scratched to see if it causes a reaction.
- Blood test. During a blood test, doctors look for IgE antibodies to specific allergens. If you have high levels of IgE for certain pollens like birch pollen, it could mean you are allergic to it. And it could mean you are at risk for OAS to pollen-related foods.
- Oral food challenge. You eat small, increasing amounts of the food while a doctor watches for a reaction. This helps tell if your symptoms are from OAS or a true food allergy.
Tips for preparing for an allergist visit
How is oral allergy syndrome treated?
There is no cure for OAS. Your doctor can help you figure out the best treatment plan based on:
- Which pollen(s) you’re allergic to
- How strong your symptoms are
- Whether you’re reacting to raw fruits, nuts or vegetables, even after cooking
Here are OAS treatment options your doctor may discuss with you.
Antihistamines
These medications help with itching and mild swelling. Some people take them before eating foods that trigger symptoms.
Non-drowsy second-generation antihistamines like cetirizine (Zyrtec®), loratadine (Claritin®) or fexofenadine (Allegra®) are often effective. Your allergist can help you choose the best option.
Allergy immunotherapy (allergy shots)
Allergy immunotherapy involves exposing a patient to small, increasing doses of an allergen. This helps the body to build up tolerance to the allergen. Building up tolerance reduces or eliminates allergy symptoms.
Allergy immunotherapy is available for pollen. They can lower your pollen sensitivity, which may also help reduce OAS symptoms.
- The injections contain tiny amounts of the pollen to which you’re allergic.
- Over time, the amount of pollen increases so your body can slowly get used to the allergen.
- This helps train your immune system not to overreact when it comes into contact with pollen.
- Allergy immunotherapy injections are usually given once or twice a week at first, then less often as the body adapts to pollen.
SLIT (sublingual immunotherapy)
This is an immunotherapy option that uses tablets or drops placed under the tongue instead of shots. SLIT is mostly approved for certain pollen allergies (like grass or ragweed). Early studies show it might help with OAS, but more research is needed.
- The tablets contain small amounts of the allergen.
- It is taken daily.
- The first dose is given in a clinic, then you can take it at home.
Epinephrine
In rare cases, people with OAS may develop a serious allergic reaction, or anaphylaxis. Symptoms affect two or more body systems. The first line of treatment is epinephrine. It is available in several forms, including a nasal spray and auto-injector. Epinephrine treats the symptoms fast.
How is oral allergy syndrome prevented?
Sometimes, no matter what you do, you may not be able to avoid foods that cause OAS symptoms. You can reduce the risk of symptoms by:
- Avoiding trigger food, especially in raw form, during pollen season.
- Cooking or microwaving the foods to break down the proteins. You can experiment with how much you need to cook the food before symptoms appear.
- Peeling fresh fruits or vegetables before eating.
- Explaining your dietary needs to chefs and wait staff when you go out to eat at restaurants. (This includes the need to avoid cross-contact in food prep.)
- Using gloves if touching a food causes an OAS reaction.
- Reading food labels and checking for ingredients with trigger foods. Look for added fruit or veggie extracts (like apple juice concentrate or celery powder).
How to manage OAS during peak pollen season
People with OAS often have worse symptoms during peak pollen season when their immune system is more sensitive. Managing these periods strategically can help prevent uncomfortable reactions.
- Avoid raw trigger foods. Even mild foods may cause stronger reactions during this time.
- Take antihistamines. Some people take them before eating trigger foods.
- Ask about allergy shots or SLIT. These may help reduce your pollen and food reactions over time.
- Check pollen counts. Use apps or weather reports to track high-pollen days.
- Plan meals ahead. Bring safe snacks and let restaurants know about your allergies.
Managing OAS is different for everyone. Consult an allergist to create a personalized plan based on your specific allergies, symptoms, lifestyle and risks.
Mental impact of oral allergy syndrome: OAS
Living with oral allergy syndrome involves more than just handling physical symptoms. It can also affect your mental and emotional health. Many people with OAS experience increased stress and anxiety, especially during pollen season. This can lead to avoiding social situations. Additionally, having a reaction to a food that was previously safe can create a fear of developing new allergies.
- Worry about eating. Uncertainty over eating a food and whether it could cause a reaction can make you anxious about food. You may also develop unhealthy eating habits by avoiding some foods without guidance from a doctor.
- Social limitations. Going out for meals, traveling, or attending social events can become stressful or even isolating, especially when others don’t understand OAS or downplay its impact.
- Fear of a worse reaction. While most OAS symptoms are mild, some people worry that their reactions could become severe, particularly if they also have other serious food allergies.
Coping and support
There are growing communities and resources available to support people living with OAS:
- Talk to a counselor. Find someone who understands allergies and anxiety.
- Learn more. Webinars, videos, and articles can help you feel more in control.
- Make a plan. Work with your doctor to create a list of safe foods and what to do during a reaction.
Knowing your triggers, having trusted treatment strategies, and feeling understood by your support network can make a huge difference in your quality of life.
Questions and Answers (Q&A) on oral allergy syndrome
Here are some commonly asked questions about oral allergy syndrome (OAS). If you have a question you’d like to see answered here, please email our editor.
Reviewed by:
Purvi Parikh, MD, FACAAI, is an adult and pediatric allergist and immunologist at Allergy and Asthma Associates of Murray Hill in New York City. She is on faculty as Clinical Assistant Professor in both departments of Medicine and Pediatrics at New York University School of Medicine.
