Seafood allergies are far more common than previously thought and twice as prevalent as nut allergies in Americans.

As many as 1 in 50 American adults may have an allergy to seafood, a telephone survey of 15,000 adults has determined.

In conducting the survey, researchers at the Mount Sinai School of Medicine in New York also found that seafood allergies usually do not emerge until adulthood and can occur even in those with no history of allergies. They can trigger reactions on the skin (such as hives), in the gastrointestinal tract or, most seriously, in the respiratory tract.

More people are allergic to shellfish (1 in 50), with shrimp, crab and lobster causing more problems than fish (1 in 250). Some reactions are so severe they can make it difficult to breathe and require a quick shot of epinephrine to prevent death.

Women were more likely to report seafood allergies than men, though it was more common in boys than girls. African-Americans reported a higher incidence than other races.