Allergic to shrimp? You may grow out of it

NEW YORK - Shellfish allergies are among the most common type of food allergy but a U.S study has found that sufferers may possibly build up a tolerance to shrimp and possibly lobster and clams as they grow older.

Shellfish allergies tend to persist into adulthood, with reactions ranging from mild symptoms, like nasal congestion and hives, to serious or even life-threatening problems such as airway constriction, but little has been known about how children and adults differ in the immune response to shrimp proteins.

But researchers from the Mount Sinai School of Medicine in New York have found that adults who are allergic to shrimp tend to have a less intense immune-system reaction to the shellfish compared with children.

For their study, reported in the Journal of Allergy and Clinical Immunology, researchers looked blood samples from 34 children and 19 adults with a history of allergic reaction to shrimp.

They found among children, blood levels of IgE antibodies against shrimp were typically four times higher compared with adults. The children's antibodies also tended to bind to more shrimp proteins, and to bind to those proteins more strongly.

Researcher Rosalia Ayuso said the findings are the first to show that children tend to have a stronger immune-system sensitization to shrimp than adults.

The researchers noted that the study did not follow participants over time, and it's not known at what age they first became sensitized to shrimp so it is unclear whether the adults were sensitized in childhood and then gradually had a reduction in their shrimp antibodies.

"However, the findings do suggest that allergic reactions to shrimp may wane with age," according to Ayuso's team.

The researchers said it may be worthwhile for adults with a history of shrimp allergy to undergo objective testing, with a food challenge, to see whether they have built up a tolerance.

Food challenges -- where an allergy patient consumes the suspect food under medical supervision to see if it triggers a reaction -- are considered the "gold standard" for diagnosing food allergies.

There are other tests as well -- the skin-prick tests and antibody blood tests -- but they are not always an accurate measure of whether a food will trigger a physical reaction.

In one recent study, Ayuso's team notes, half of participants with either a history of reactions to shrimp or positive results on skin-prick or blood testing were able to eat shrimp proteins without a problem during a food challenge.