What is oral allergy syndrome?
Oral allergy syndrome, also called pollen food allergy syndrome or PFAS, is a type of food allergy caused by certain allergens found in both pollen and raw vegetables and fruits and some nuts. People affected with this syndrome can tolerate the cooked form of the same fruit or vegetables. However, they develop an allergic reaction upon consuming them raw. This may occur due to the allergen being destroyed by the heating process, which no longer provokes an immune response in the body. Oral allergy syndrome is generally seen in older children, teens and adults. It is the most common food allergy seen in adults. Often, this allergy starts abruptly. People may report consuming the offending fruit or vegetables for years without having any allergic reaction. Some people with PFAS may have a history of hay fever or allergic rhinitis after exposure to the pollen. The same allergen that caused the allergy to pollen incites the immune system to cross-react with other foods at some point in time.
What are the symptoms of oral allergy syndrome?
Unlike pollen allergy that typically has a seasonal variation, oral allergy syndrome can occur any time of the year. The symptoms, however, are generally most noticeable during the related pollen season and for a few months after. It is a type of contact allergic reaction, which means the symptoms appear when a particular food comes in contact with the mouth and throat of the affected person. The symptoms generally include itching and swelling of the mouth, lips, tongue, face and throat. The itching typically begins immediately after the food is put in the mouth. It may last for a few minutes after the food is swallowed. Rarely, the symptoms may take hours to develop. Although not common, some other symptoms may also develop, such as nausea, stomach upset and vomiting. Some people may also report getting itchy, red hands when peeling raw vegetables, such as white potatoes.
The symptoms of oral allergy syndrome are generally mild. Rarely, however, they can cause severe reactions, such as excessive swelling of the throat that perturbs swallowing and breathing. A few people may develop a generalized severe reaction called anaphylaxis. This is characterized by chest tightness, difficulty breathing and even loss of consciousness. Severe reactions need urgent medical attention. Although severe reactions are rare, avoiding the offending food is advisable. Generally consuming the food in canned or cooked form causes no problem. If you had a severe or generalized reaction in the past or have any nut allergies, your doctor may prescribe an epinephrine auto-injector.
What foods cause oral allergy syndrome?
Oral allergy syndrome is usually caused by raw foods of plant origin, such as uncooked vegetables, raw fruits, spices and some tree nuts. Nuts can also trigger allergic reactions unrelated to pollen that can be severe. Hence, people with nut allergy must exercise extreme caution.
Table. Common allergens and the associated foods
| Allergen | Associated food |
| Birch pollen | Apple, almond, carrot, celery, cherry, hazelnut, kiwi, peach, pear, plum, hazelnuts, peanuts, aniseed, soybeans, caraway, fennel, parsley |
| Grass pollen | Celery, melons, oranges, peaches, tomato, peanuts, Swiss chard |
| Ragweed pollen | Banana, cucumber, melons, sunflower seeds, zucchini, kiwi |
Most people do not get an allergic reaction to a range of foods. The reaction is typically confined to one or a small number of foods. Furthermore, the allergy may be limited to a particular variety of fruit. For instance, Granny Smith apples cause more cases of oral allergy syndrome than Fuji apples.
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