Oral Allergy Syndrome (OAS)

Oral allergy syndrome is a unique and uncommon phenomenon, also known as pollen-food allergy syndrome. It can affect one out of three people who have seasonal allergies. Due to the rarity and unawareness of this medical condition, the actual incidence is likely under-reported.

Oral allergy syndrome occurs in a person with a history of hay fever who is allergic to airborne allergens such as pollen and grass. In oral allergy syndrome, the affected person has a concurrent allergic reaction to raw fruits, vegetables, or nuts. One can develop oral allergy syndrome despite being able to tolerate certain fruits or vegetables over the years. The allergy symptoms tend to be seasonal and exacerbated during the pollen season.

Oral Allergy Syndrome seldom occurs in children. This condition is more frequently seen in older children and adults.

What type of allergy is oral allergy syndrome?

Oral allergy syndrome is an IgE-mediated form of allergy. Immunoglobulin E (IgE) is a type of antibody that the body produces when the body’s immune system reacts exaggeratingly against an allergen/protein. IgE can trigger a cascade of chemicals and inflammatory cells in the body, leading to an allergic clinical presentation. In oral allergy syndrome, the IgE effect is localised to the mouth and throat region, leading to itching and swelling in the affected area.

What is the cause of oral allergy syndrome?

The actual cause of oral allergy syndrome remains unknown. It is stipulated that airborne allergens such as grass, common weed, and pollen may have similar proteins as certain fruits and vegetables, leading to a cross-reactivity of the proteins between the two groups of substances. One typically has background asthma or allergic rhinitis (hay fever), airborne allergies against grass, pollen, and common weed, and further immune sensitisation when consuming raw fruits, vegetables, or nuts. 

Interestingly, for the allergic reaction to occur, the person must be exposed to pollen or grass first so that the immune system can recognise the pollen-related allergens. Upon later exposure to raw fruits or vegetables, the immune system recognises the cross-reactive protein between pollen and fruits/vegetables, thus mounting an allergic immune response. In other words, if a person has never been exposed to pollen allergens, the person will not develop fruit-vegetable allergies.

What are the symptoms associated with oral allergy syndrome?

Allergy symptoms associated with oral allergy syndrome tend to be mild, though symptoms can be worsened during the pollen season.

Common symptoms of oral allergy syndrome include localised symptoms such as:

• Itching, tingling of lip, mouth, tongue, throat
• Swollen lip, tongue, throat
• Hives over the mouth or lips
• Sore throat

Occasionally one may also develop itching, rashes, or mild swelling over their fingers and hands when handling or peeling raw fruits and vegetables. Less commonly, there may be other gastrointestinal symptoms such as nausea, vomiting, or diarrhoea following swallowing the culprit food into their alimentary system.

In rare cases, oral allergy syndrome can be associated with anaphylaxis. In anaphylaxis, catastrophic and life-threatening systemic allergic symptoms can occur, such as acute shortness of breath, airway tightening, facial/lip/eye swelling, generalized rash, feeling of impending doom, and fainting. One can succumb to anaphylaxis and should seek medical attention immediately to reverse the allergy.

Curiously, as oral allergy syndrome is a seasonal condition, one may be able to tolerate a particular fruit, vegetable, or nut on normal occasions but develop allergy symptoms during pollen season.

What are the common pollens that can be associated with oral allergy syndrome?

• Birch tree
• Timothy grass
• Bermuda grass
• Bahia grass
• Johnson grass
• Common Ragweed

What are the common fruits that are associated with oral allergy syndrome?

Season	Pollen	Food that has similar protein cross-reactivity with pollen
Spring	Birch tree	Nuts and legumes: • Almond • Hazelnut • Peanut • Soya bean	Fruits: • Peach • Pear • Plum • Apple • Apricot • Cherry • Kiwi • Carrot	Vegetables/Seeds: • Potato • Pumpkin seed • Celery • Parsley
Summer	Grass	Fruits: • Melon • Orange • Tomato • Peach • Kiwi
Fall	Ragweed	Fruits/Seeds: • Melon • Banana • Cantaloupe • Cucumber • Zucchini • Sunflower seed

Can I tolerate cooked food if I have oral allergy syndrome?

Interestingly, if the food is cooked, you are likely to be able to tolerate it, as the protein (cross-reactive protein between pollen and fruits) is broken down following high temperature, and the body will not mount a response to cooked fruits/vegetables.

What should I do if I suspect I have oral allergy syndrome?

If you have allergy symptoms, you are advised to seek medical attention. In a dire situation of anaphylaxis, you should seek medical aid immediately. In stable allergy symptoms, your doctor will obtain further medical and social history of your symptoms. It would be useful if you could identify any possible triggers for your allergy symptoms. If there is concern of airborne or food allergies, your doctor may advise you to undergo further allergy testing.

What tests can we consider to evaluate for oral allergy syndrome?

If there is suspicion of oral allergy syndrome, your doctor may recommend allergy tests, such as a skin prick or blood test (RAST test), to confirm your allergy to pollen and food. You can discuss your allergy symptoms with your doctor, and your doctor can guide you and narrow down the possible triggering allergens for testing.

How is oral allergy syndrome treated?

Identifying the food allergens and avoiding the food that causes allergy is key.

Your doctor or allergist can help you identify the culprit allergens.

In mild allergy symptoms, antihistamines and steroids can alleviate your symptoms.

In life-threatening allergy symptoms such as anaphylaxis, adrenaline may be required to reverse the allergy.

How can I prevent oral allergy syndrome?

• Avoid culprit food that is associated with your allergy.
• Ensure pollen-cross-reacted food (fruits, nuts, vegetables) is cooked well if needed.
• Before consuming, you can consider baking, microwaving, cooking, or heating your fruits or vegetables.
• The outer skin layer of the fruits can be peeled to prevent allergy symptoms.

In conclusion…

• Oral allergy syndrome, also known as pollen-food allergy syndrome, can be triggered by raw fruits, vegetables, and nuts.
• Oral allergy syndrome occurs in people who have concurrent allergies to pollen.
• Common symptoms of oral allergy syndrome include mild allergic symptoms over the oral area minutes after consuming the culprit food.
• Rarely, oral allergy syndrome can cause anaphylaxis, which requires immediate medical attention to reverse the life-threatening allergy.
• Oral allergy syndrome is likely due to the cross-reactivity between proteins found in pollen and raw fruits/vegetables.
• Allergy tests, such as skin prick tests or RAST tests, may be beneficial in identifying airborne and food allergens.
•  By identifying the culprit allergens, one can avoid oral allergy syndrome by avoiding the culprit food.

References

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2. Carlson G, Coop C. Pollen food allergy syndrome (PFAS): A review of current available literature. Ann Allergy Asthma Immunol. 2019; 123(4):359-365.
3. Hussein H, Mensah RK, Brown RS. Diagnosis and Management of Oral Allergy Syndrome, the Itchy Tongue Allergic Reaction. Compend Contin Educ Dent. 2019; 40(8):502-505.
4. Muluk NB, Cingi C. Oral allergy syndrome. Am J Rhinol Allergy. 2018; 1;32(1):27-30.
5. Ma S, Sicherer SH, Nowak-Wegrzyn A. A survey on the management of pollen-food allergy syndrome in allergy practices. J Allergy Clin Immunol 2003; 112:784.