Q. I’m 32 and just had my first anaphylaxis experience to shrimp. It was scary: I was wheezing and could hardly breathe. How can a grown woman suddenly develop a food allergy?
Dr. Scott Sicherer: You are not alone in developing shrimp allergy as an adult. In our U.S. prevalence studies and studies in Canada that tracked peanut, tree nut, fish, shellfish and sesame allergies, shellfish was the most common self-reported allergy.
We know food allergies are affected by the immune system, heredity, environmental factors, and the characteristics of the foods themselves. We know that many food allergies are outgrown, so there are clearly differences between children and adults. What we are missing are the exact details underlying each factor and how the factors interrelate. We only have theories to address your question.
The characteristics of food proteins likely play a role. Proteins responsible for persistent and severe allergies are more resistant to digestion and more likely to be recognized by the immune system. It may be that the child’s immature gut or immune system is more prone to attack the proteins, but shrimp may be an example of a protein that is particularly capable of triggering an immune attack even for adults.
A route of exposure other than through the mouth may be a contributing problem for adult-onset allergy. Most food allergies that begin beyond childhood are mild reactions to raw fruits and vegetables. This type of allergy is called oral allergy syndrome and is related to proteins in pollens. For example, apple shares similar proteins with birch pollen. Thus, becoming allergic to similar proteins in the air starts the trouble.
A theory has also been proposed that environmental exposure to peanut, without actually eating peanut, may increase the risk of peanut allergy. Interestingly, shellfish proteins are similar to ones found in dust mite and cockroach, although most people with those allergies tolerate shellfish.
Next: Digestion Changes