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Fast fact: Oral allergy syndrome can strike at any time of the year. However, allergic reactions are more common during spring and summer, when plants are flowering and the air is full of pollen.In summer, there’s plenty of fresh fruit to be had. Most of us enjoy the abundance of local berries, peaches, and melons. Yet some people would rather stay far away from fruit. Why? Because they have oral allergy syndrome (OAS), a condition that causes itchiness and swelling in the mouth and throat when eating some fruits, vegetables, and nuts.
The allergic reaction actually occurs because of proteins on the surface of fruit, not its flesh. Here, the word protein refers to structural protein, which in fruits skins has a similar structure to pollen (a very common allergen). The likelihood of developing OAS actually increases with exposure to pollen.
What causes allergic reactions? Well, your body produces an antibody called immunoglobulin E (IgE) when it encounters an allergen. In the case of OAS, IgE antibodies that react to pollen also react to the proteins on fruit skins. This is called cross-reactivity.
Fast fact: Oral allergy syndrome occurs in up to 70% of seasonal hay fever sufferers.However, OAS is not associated with just one type of pollen allergy. Usually, if you have an allergy to pollen from certain plants, you will also react to specific types of fruit. For example, people allergic to grass are likely to react to melons, oranges, and tomatoes. Those allergic to alder tend to react to apples, cherries, peaches and pears.
Antibodies can recognize different proteins with similar structures because the active site (where the protein attaches to the antibody) only covers part of the protein. In other words, antibody looks for specific patterns in the protein. As long as the protein has those patterns, the antibodies will react. Also, the reaction may not be the same with all matching proteins. Some proteins may cause stronger reactions than others.
Fast fact: Structural proteins support the structure of the fruit skins. They are also found in your skin and hair.How do you treat OAS? The same way as you would treat any other allergy. The best way is simply to avoid the allergen: don’t eat the offending fruit. But if you’re really craving fruit, peeling or cooking can also help avoid an allergic reaction.
Peeling fruit physically removes the proteins that cause OAS, while heat from cooking denatures them. When a protein is denatured, it loses its original shape and function. As a result, the IgE antibodies no longer recognize it.
However, some people with more severe pollen allergies can’t even touch fruit. About 2% of OAS cases result in anaphylaxis, severe swelling that starts in the throat and can result in death.
Fast fact: Proteins have many different functions. Antibodies are a special type of protein that can recognize other proteins.So the next time someone makes funny faces when you offer them fruit, don’t assume they’re a picky eater. They may be anticipating an unpleasant allergic reaction. In the most severe cases, it may even be a matter of life and death.
General news and science websites
Oral Allergy Syndrome (Daniel More, About.com) Oral Allergy Syndrome Foods, Symptoms, Treatments, and More (Neil Osterweil, WebMD.com) Protein Function (Regina Bailey, About.com)
Oral Allergy Syndrome Fact Sheet (Canadian Food Inspection Agency)
Frank SA. 2002. Specificity and Cross-Reactivity, p 33-54. In Immunology and Evolution of Infectious Disease, Princeton University Press, Princeton, NJ. http://www.ncbi.nlm.nih.gov/books/NBK2396 Sussman G, Sussman A, Sussman D. 2010. Oral Allergy Syndrome. Canadian Medical Association Journal. 182(11):1210-1211. http://www.cmaj.ca/content/182/11/1210.full