Immediate symptoms of itching or tingling of the mouth upon ingestion of certain foods is termed oral allergy syndrome (OAS). The reaction usually stays local and mostly occurs to raw foods but a small percentage of patients with oral allergy are at risk for more severe reactions, even to cooked or processed foods. For some people with OAS, it is a warning sign of emerging more severe food allergies. For most OAS patients eating or drinking a concentrated amount of the food allergen may lead to a more severe reaction including anaphylaxis so it’s best not to push your luck.
Causes:
In many cases, OAS is due to cross-reacting respiratory allergies. It may start with the development of allergic antibodies to pollens or even natural rubber latex. Then, since the proteins in certain foods are similar to those in respiratory allergens, the allergic antibodies interact with the foods and cause release of histamine. In some ways, it is like eating pollen–or so the body thinks.
Prognosis:
Most OAS patients never have symptoms beyond the mouth. Some have heartburn or other digestive problems if they continue to eat the foods but only a minority have serious reactions. OAS tends to be a milder form of food allergy because the food allergens are labile and readily destroyed by cooking or digestive acid/enzymes.
However, for about 9% of people with oral allergy from fruits there are symptoms outside of the intestinal tract and about 2% experience anaphylactic shock. Those who have oral allergy but are not allergic to pollens are at higher risk since they are allergic to different proteins called LTPs (Lipid Transfer Proteins) which are less likely to be degraded during digestion.
Common respiratory allergen and food pairings* include:
| Airborne allergen | Food |
| Birch pollen | Vegetables: carrot, celery, parsley |
| Fresh fruit (apple, apricot, cherry, kiwi, mango, nectarine, peach, pear, plum) | |
| Nuts: Almond, Hazelnut, Peanut | |
| Soybean | |
| Grass pollen | Orange, Tomaro, Peach, Watermelon, White Potato |
| Ragweed pollen | Bananas |
| Melons (cantaloupe, honeydew, watermelon) | |
| Latex | Bananas |
| Avocado | |
| Kiwi | |
| Chestnuts | |
| Others occasionally including tomato, eggplant, melons |
Diagnosis:
Skin testing to foods in patients with OAS is often negative since the labile proteins in the foods may be degraded the manufacturing process. If an OAS patient tests positive to foods they may be at higher risk for anaphylaxis since they are likely allergic to sturdier proteins.
Treatment:
There is no “cure” for OAS but some people find that they improve with allergy shots (immunotherapy) given for hayfever. If skin testing is positive to some foods in the setting of OAS it may be prudent to carry an Epipen.
The American Academy of Allergy has a helpful chart too!