Oral allergy syndrome
An allergic reaction confined to the mouth and throat after eating raw fruit or vegetables, caused by cross-reactivity with pollens.
Oral allergy syndrome, also called pollen-food syndrome, causes tingling, itching or mild swelling of the lips, mouth and throat within minutes of eating certain raw fruits or vegetables. It is the most common form of food allergy in adults.
Its mechanism is cross-reactivity: the immune system, sensitised to a pollen, recognises proteins with a similar structure in certain plants. The classic associations are birch pollen with apple, cherry, peach, hazelnut and carrot; mugwort with celery, carrot and spices; and grasses with tomato and melon.
Cooking generally removes the reaction, and this is the most useful point in practice: the proteins involved are heat-sensitive. Someone who reacts to raw apple usually tolerates apple purée or apple pie. Peeling the fruit, or eating it when fully ripe, also often reduces symptoms. There is therefore no need to cut out the food altogether.
Two important caveats. Symptoms often follow the pollen season: they get worse in spring for birch. And although reactions are usually mild and localised, more severe forms exist, particularly with tree nuts. Any symptom beyond the mouth and throat calls for an opinion from an allergy specialist.