Oral Allergy Syndrome: What It Is and Why It Happens

Imagine biting into a juicy apple and suddenly feeling your mouth itch or your throat tingle. If you have hay fever or seasonal allergies, this may be more than just a coincidence, it could be Oral Allergy Syndrome (OAS).
​ 
This condition is a type of food allergy that occurs in people sensitive to pollen and is caused by an immune system mix-up.
 
Today I’m going to explore what OAS is, why it happens, and how it connects to conditions like eczema and gut health.

What Is Oral Allergy Syndrome?

​OAS, also called pollen-food syndrome, is an allergic reaction that occurs when your body confuses proteins in certain raw fruits, vegetables, nuts, and seeds with proteins in pollen. For example, if you’re allergic to birch pollen, eating a raw apple may trigger a reaction because the proteins in the apple are like those in the pollen. (1,2)
 
Common Symptoms
Symptoms usually happen right after eating a trigger food and include:

• Itching or tingling in the mouth or throat
• Swelling of the lips, tongue, or throat
• Mild irritation or redness in these areas

 
Fortunately, these reactions are usually mild and short-lived. Cooking or peeling the food often eliminates the problem because heat and food preparation methods change the structure of the proteins.

Which Foods Can Trigger OAS?

​The foods that cause OAS depend on the type of pollen allergy you have:

1. Birch Pollen Allergy: Apples, pears, cherries, carrots, hazelnuts, almonds
2. Ragweed Pollen Allergy: Melons (cantaloupe, watermelon), bananas, cucumbers, courgettes
3. Grass Pollen Allergy: Tomatoes, peaches, celery, melons, oranges
4. Mugwort Pollen Allergy: Celery, carrots, parsley, coriander

 
If you notice that certain foods bother you, especially during pollen season, OAS might be the reason.

Why Does OAS Happen?

​OAS is caused by cross-reactivity in the immune system. This happens when your body mistakes harmless food proteins for pollen proteins it’s already allergic to.
 
Your immune system creates antibodies (called IgE) to fight off what it sees as harmful invaders. If you have hay fever, these antibodies target pollen proteins. But because the proteins in some foods look so much like pollen, they also trigger the same response. This is why you might get allergy symptoms even though the food itself isn’t dangerous.

Is There a Link to Eczema or Other Skin Conditions?

OAS doesn’t just cause discomfort in the mouth and throat, it can also affect your skin, especially if you have eczema.
 
The connection lies in how your immune system works when you have what’s known as an atopic condition. If you have eczema, hay fever, or asthma, your immune system tends to overreact to harmless substances, whether they come from the environment or your diet. These conditions, often grouped under the term "atopic disease," mean your immune system is more sensitive than average, and that same sensitivity can make you more prone to OAS.
 
When you eat a food that triggers OAS, your immune system mistakenly sees the food proteins as harmful, similar to how it reacts to pollen. This leads to the release of histamine, a chemical that causes inflammation and allergy symptoms like itching and swelling. If you already have eczema, this inflammation can spill over into your skin, worsening your symptoms or triggering flare-ups. Even a small increase in inflammation can lead to noticeable itchiness or irritation for those with sensitive or already inflamed skin.
 
In some cases, the foods that trigger OAS may directly impact your skin as well. For example, you might notice that eating raw apples, nuts, or other OAS-related foods not only causes mouth symptoms but also makes your eczema worse. This could be because your immune system is already on high alert or because food allergens are interacting with your skin's barrier, which may already be compromised in eczema.
 
If certain foods seem to make your eczema worse, it might be worth exploring whether there’s a link to your pollen allergies. Consulting with a GP, allergist, or nutrition practitioner can help you identify these connections and develop a plan to manage both OAS and eczema more effectively.
 
Gaining a better understanding of these relationships not only helps you avoid triggers but also gives you a deeper insight into how your immune system, diet, and skin health are all interconnected.

Could Gut Health Be Involved?

​There’s growing evidence that your gut health plays a central role in managing allergies, inflammation, and even skin conditions like eczema. Your gut is a major hub for your immune system, and its condition can significantly influence how your body reacts to allergens and regulates inflammation. This “gut-skin-immune connection” can offer clues about how improving your gut health may help with conditions like OAS and eczema.
 
The gut is home to trillions of microorganisms, collectively known as the gut microbiota, which include bacteria, fungi, and other tiny life forms. These microbes play a crucial role in maintaining a healthy immune system. A diverse and balanced microbiome can keep inflammation in check and prevent overreactions to harmless substances like pollen or food proteins. On the other hand, when the microbiome is out of balance, a state called dysbiosis, it can make the immune system more reactive, increasing your chances of experiencing inflammation, allergies, and skin problems.
 
Another vital aspect of gut health is the integrity of the gut lining, sometimes called the gut barrier. This lining acts like a sieve, letting nutrients pass through while keeping harmful particles out of the bloodstream. When the gut lining becomes weakened, a condition often referred to as "leaky gut", larger food particles, toxins, and bacteria can escape into the bloodstream. This can trigger an immune response, leading to increased inflammation. For people with OAS, this might mean heightened sensitivity to certain foods. For those with eczema or other skin conditions, the resulting inflammation can worsen flare-ups or skin irritation.
 
Supporting your gut health can be a simple yet powerful way to calm your immune system and reduce allergic reactions. Eating a diet rich in fibre, such as whole grains, fruits, and vegetables, helps feed beneficial bacteria in your gut, promoting a healthy microbiome.
 
Adding fermented foods like yoghurt, kefir, and sauerkraut introduces probiotics or “good bacteria” that can restore balance in your gut. Prebiotic foods, such as onions, garlic, and green bananas, serve as fuel for these beneficial bacteria, further supporting their growth and activity. Together, these strategies can help reduce inflammation, regulate your immune system, and improve overall health.
 
By focusing on gut health, you’re addressing one of the root causes of inflammation and allergic conditions. Whether you’re managing OAS, eczema, or general inflammation, paying attention to this gut-skin-immune connection can lead to long-term relief and better overall wellbeing. Making small, manageable changes to your diet can have a ripple effect on your immune system and skin, helping you feel healthier and more in control.

How Can You Tell If You Have OAS?

If you think you might have Oral Allergy Syndrome (OAS), it’s important to get a proper diagnosis from a qualified medical practitioner, such as your GP or an allergy specialist. They can assess your symptoms, perform any necessary tests, and rule out other potential conditions.
 
Once diagnosed, working with a Registered Nutritional Therapist can help you understand how to manage your symptoms through tailored dietary strategies whilst ensuring your nutritional needs are met.
 
Tips for managing symptoms while maintaining a healthy diet:
 
Living with OAS doesn’t mean you have to give up your favourite fruits and vegetables forever. Here are some tips for managing symptoms while maintaining a healthy diet:

1. Cook or Peel Foods: Heating and peeling often destroy the proteins that cause reactions. For example, cooked apples or carrots are usually safe for people with OAS.
2. Be Cautious During Pollen Season: Your immune system is more reactive during this time, so symptoms might worsen.
3. Support Your Gut: Eating a balanced diet with plenty of prebiotic and probiotic-rich foods can strengthen your gut health.
4. Work with a Professional: A Registered Nutritional Therapist can help you plan a diet that avoids triggers while keeping your nutrition balanced.

 
Oral Allergy Syndrome is a unique and manageable condition that highlights the complex connection between your diet, immune system, and environment. By understanding your triggers and learning how to manage them, you can reduce symptoms and enjoy a diverse, nutritious diet.
 
If you think you have OAS or want to explore how it might connect to other conditions like eczema or gut health, seeking advice from a healthcare professional or nutrition practitioner is a great first step.
 
With the right support and strategies, you can keep your allergies under control and focus on living a healthier, happier life.

References

1. Muluk NB, Cingi C. Oral Allergy Syndrome. Am J Rhinol Allergy [Internet]. 2018 Jan 1;32(1):27–30. Available from: https://doi.org/10.2500/ajra.2018.32.4489
2. Skypala IJ. Can patients with oral allergy syndrome be at risk of anaphylaxis? Curr Opin Allergy Clin Immunol [Internet]. 2020;20(5). Available from: https://journals.lww.com/co-allergy/fulltext/2020/10000/can_patients_with_oral_allergy_syndrome_be_at_risk.7.aspx