For many people with hay fever, eating certain foods can actually trigger an allergic reaction in the mouth, making them think they have a mild food allergy. For example, cantaloupe can cause itching or hives, or eating uncooked apples may do the same to people with birch pollen allergy.
This is called “oral allergy syndrome,” (OAS), and it is estimated that up to a third of pollen allergy patients may be affected. Most cases are mild, but some can be an early warning sign of a serious, life-threatening severe allergic reaction called anaphylaxis. It’s easy to see why people confuse OAS with traditional food allergies.
OAS is the immune system simply trying to protect the body. Ihay fever (also called “seasonal allergies” or “outdoor allergies”), the immune system misreads certain inhaled pollens as dangerous particles. It triggers sneezing, runny nose, watery or itchy eyes, and other unpleasant symptoms to flush these foreign particles out of the body.
In OAS, the immune system treats proteins similar to those in pollen that are sometimes found in fruits or vegetables the same way. This “cross-reactivity” is a result of the immune system recognizing that the proteins in these foods are similar (although not exact) and an allergic reaction is the result.
Here are foods that may have proteins that cross-react with certain pollen:
Ragweed Allergy: Ragweed cross-reacts with bananas and melons, so people with ragweed allergies may also react to honeydew, cantaloupe, and watermelons, or tomatoes. Zucchini, sunflower seeds, dandelions, chamomile tea, and Echinacea may also affect some people.
Birch Pollen Allergy: People with birch pollen allergies may react to kiwi, apples, pears, peaches, plums, coriander, fennel, parsley, celery, cherries, carrots, hazelnuts and almonds.
Grass Pollen Allergy: People with grass allergy may react to peaches, celery, tomatoes, melons, and oranges.
Natural Rubber Latex (NRL) Allergy: Like pollen allergy, people allergic to natural rubber latex may react to bananas, avocados, kiwi, chestnut, and papaya. Of course, if your food is handled by a person wearing latex gloves and you have a latex allergy, you may actually be reacting to cross-contamination of latex particles on the food.
If this all sounds confusing, you’re right. That’s why it’s critical to always consult with a healthcare provider for a complete diagnosis of your allergies. It could be OAS, food intolerance, another type of food-borne illness, food poisoning or something entirely different.
A healthcare professional will ask if you have OAS symptoms and about the foods you eat and will do test to understand your other allergies. Oral sensitivity tends to develop over time, with repeated exposures to inhaled pollens. Many doctors report that most of their patients with OAS are adults.
A healthcare provider may administer a skin-prick test. A bit of the protein trigger is included in a light scratch on your back or forearm. If that spot turns red or swells in about 15 minutes, it's likely an allergic reaction.
Either this is mainly oral allergy and not to worry, or this could be more serious and you need to take precautions, such as carrying epinephrine with you at all times for emergency treatment for yourself.
A recent study shows that in about 2% of patients with OAS, oral allergy symptoms could progress to anaphylaxis, a serious reaction that could be deadly without immediate emergency treatment.
The basic plan: If a food makes you have bad symptoms, avoid that food. Cooking may help, as heat breaks down or alters the trigger proteins so that the immune system may not target them. Peeling or canning fruits and vegetables may also help some people, because most trigger proteins are in the outer skin or peel, but this is not always the case.
The best plan is always to speak with your healthcare provider, get properly diagnosed, keep a list of your trigger foods and never eat anything that causes your symptoms.