Allergist and Immunologist Questions Food Allergy

Strange allergy, what is it?

I have a slight allergic reaction whenever I eat certain things, including many raw fruits/vegetables/nuts. When they are cooked or altered, I do not experience the allergy. It's an itchy feeling in my mouth, lips, and throat. I do not experience swelling -- just itchy discomfort. Could I really be allergic to all of those foods or is it something else?

8 Answers

It is something else!!! The condition is known as oral allergy syndrome. Usually happens to people who have sensitivities to trees pollens, because of cross-reactivity between the fresh stone fruits/nuts and tree pollens. Cooked fruits don’t cause problems since temperature changes the tertiary structure of an allergen and it doesn’t remind a tree pollen allergen anymore.
Yes, this is a type of allergy called food-pollen syndrome. This is due to a cross reacting allergen between certain pollens and certain fruits and vegetables. Each pollen has a list of crossing reacting foods. The allergen is heat lability and is denatured to a non allergenic form by heating.
This sounds like Oral Allergy syndrome. This reaction, typically itching in the mouth after eating fresh fruit and some veggies is due to proteins on the fruit and on pollens that look the same to the immune system. Classically birch pollen cross reacts to proteins in apples.
What you are experiencing is not strange at all. It is called oral allergy syndrome - OAS for short. Believe it or not, it is an extension or a result of your inhalant (pollen) allergies. 
When we develop allergic (IGE) antibodies to certain pollens - ragweed, some grasses and minor weeds and birch tree pollen - those antibodies make the immune cells in the oral cavity (mouth, tongue, the back of the throat) react to certain fresh or raw fruits and/or vegetables. Families of proteins are shared between those fruits and vegetables and the pollens and so the immune response is triggered or stimulated. The most common foods involved are apples, stone fruits, melons, carrots and celery, cucumber, bananas, kiwi, avocado. At times, peanuts and tree nuts can trigger such symptoms. When those foods are processed or  cooked the proteins change their form so the immune system is not activated as it does not recognize the food as a trigger any longer. 

The good news about this syndrome is that it is fairly benign and there is less than 0.5% of systemic or anaphylactic reactions so we usually do not prescribe an epinephrine in such cases. You can safely continue to consume the offending foods in their "cooked/processed" forms, just avoid eating them raw/fresh. Some patients who do allergen immunotherapy or allergy shots for their inhalant allergies notice less or even no reactions to the foods over time, but not everyone experiences an improvement to a degree to allow them to freely eat the foods. So, not much to worry about.
Thank you for the question and hope this helps you in some way.

Monika Korff, MD
You have what is called the oral allergy syndrome. You are allergic to a variety of pollens that are related to a protein found beneath the skin in certain vegetables and fruits. The exposure only occurs when you bite into the fresh fruit or vegetable. Salivary enzymes destroyed a protein before you can swallow it, so the reaction occurs only in your mouth. Cooking the food item destroys the protein, so you do not experience it with cooked foods. Cutting into the fruit or vegetable away from the skin will also help avoid the reaction. Desensitizing to the pollen will eliminate the oral reaction, and this is the only type of food allergy that can be treated with allergy shots.
Hi, you most likely have oral allergy syndrome (OAS). This occurs because there can be cross-reactivity between pollen proteins and the proteins seen in raw fruits and vegetables. Cooking the food in questions seems to alter the protein structure enough so that your body no longer reacts to it. Not surprisingly, we see this reaction in patients with pollen allergy, so they often have concurrent nasal, ocular, or respiratory allergy symptoms. If you do have OAS, there should be no risk of anaphylaxis; the symptoms are just limited to the itching of the mouth and throat. Some of our patients will continue to eat the foods in question because they like the foods and can tolerate the itching. Others don=E2=80=99t like the oral discomfort and will avoid the raw fruits and vegetables that trigger these responses. Interestingly, many of our patients who undergo allergen immunotherapy (allergy injections) to desensitize themselves to environmental allergens find that when their sensitivity to pollens decreases, their OAS also diminishes. I would still recommend that you see an allergist who can help you differentiate between OAS and true food allergy, which carries a different risk level.

Duane Wong MD
This is consistent with OAS, or oral allergy syndrome. Your symptoms are consistent with a cross-reacting allergy between fruits/vegetables/nuts and certain pollens. Your are probably allergic to the pollens first and react to these foods because the proteins are similar in structure.
You have something quite common called Oral Allergy Syndrome (also known as Pollen-Food Syndrome). The most common reason why this happens is due to allergies to birch pollen, but there are other culprits.
Please take a look at this link: