In the U.S., nearly 3 percent of adults report a shellfish allergy. It is the most common food allergy in adults. Rates are even higher in parts of Asia and Europe.
Unlike peanut or milk allergies, which frequently begin in early in North American children, shellfish allergies tend to show up later in life.
Often, people enjoy eating shellfish years before symptoms like a swollen tongue, hives, itching, or even anaphylaxis suddenly strike. Shellfish include crustaceans such as shrimp, lobster and crab, as well as mollusks like oysters, mussels, clams, octopus and scallops.
“It’s sad for adult patients. They love eating shellfish,” says Dr. Douglas Mack, assistant clinical professor of pediatric allergy, asthma and immunology at McMaster University in Ontario, Canada. “It’s a part of their culture and part of their lives.”
For years, doctors could offer little beyond the advice to strictly avoid the allergens. But the tide is beginning to shift.
Some allergists are rethinking the blanket recommendation that a reaction to one type of shellfish means all must be off the menu. It’s similar with finned fish – an allergy to one fish doesn’t always mean an allergy to all.
Can Seafood Allergies Be Treated?
Progress is also being made on treatments. In 2024, the Food and Drug Administration approved omalizumab (Xolair) to reduce allergic reactions in people with multiple food allergies. While it’s approved only to protect against accidental exposures, some people in the OUtMATCH clinical trial that led to its approval could eat substantially more of their allergens.
Allergists are hopeful that omalizumab will enable some patients to safely introduce shellfish or fish into their diets.
There’s also growing interest in using oral immunotherapy (OIT) to desensitize patients. In one small study, teens with shellfish or fish allergy were desensitized using shrimp and cod powder. Plus, an Australian institute plans a larger trial of shrimp OIT soon in Singapore.
Dr. Edwin Kim says that until recent times, food allergy management “was all about avoidance. Now the field is much more focused on treatments,” says the division chief of pediatric allergy and immunology at University of North Carolina at Chapel Hill.
Shrimp: The Most Common Offender
Among shellfish, shrimp is the most common trigger, says Andreas Lopata, PhD. An expert on allergenic proteins in shellfish and fish, he leads the Molecular Allergy Research Laboratory at James Cook University’s Australian Institute of Tropical Health and Medicine.
Shrimp’s major allergen is the muscle protein tropomyosin (Pen a 1). Found across crustaceans and mollusks, it’s responsible for much of the cross-reactivity that can occur between shellfish species.
But diagnosing shellfish allergy can be tricky. Scientists have identified at least 11 other allergens in shellfish, and there are likely more, Lopata says.
Sensitization patterns to those other allergens tend to vary by region. The patterns often reflect the shellfish species that are fished and consumed in an area, says Sahel Heidari, a doctoral candidate in allergy whose research at James Cook focuses on shellfish allergies.
Tropomyosin levels also vary by species, as do the amino acid sequences that make up the proteins.
Together, these differences help explain why someone might react to one type of shellfish but tolerate another, Lopata says. Research shows that the tropomyosin in shrimp, lobster and crab is more similar and more likely to cross-react than the tropomyosin in mollusks. Mollusks also tend to have lower levels and fewer other allergens.
“Usually, if you react to shrimp, you’ll react to crab and lobster too,” says Mack, who has a large allergy practice near Toronto. “But I have families who can eat crab even though they’re allergic to shrimp.”
Skin testing can be unreliable, Mack adds. An analysis by Lopata and colleagues of shrimp, crab, lobster, oyster and clam extracts from six manufacturers found up to a 14-fold variation in the amount of allergen detected, as well as differences in the types of allergens in the extract.
Could Dust Mites Be a Trigger?
Another source of shellfish sensitization might not be the ocean, but your home.
The protein tropomyosin is also found in house dust mites, a common indoor allergen. Some experts believe dust mite sensitization might play a role in triggering or worsening shellfish allergies, especially in adolescence or adulthood.
In a Swedish study, about half of the adults sensitized to shrimp were also sensitized to dust mites, and vice versa. Those with both were more likely to report wheezing, swelling and breathing problems.
Could treating dust mite allergy reduce shrimp reactions? Possibly. One study found that after a year of dust mite immunotherapy, some shrimp-sensitized patients had negative skin test reactions and lower shrimp-specific IgE. Unfortunately, this didn’t translate to increased tolerance during food challenges.
And the reverse may also happen: there have been reports of people becoming sensitized to shrimp after undergoing dust mite immunotherapy, Lopata says. Other studies have shown no effect either way.
The takeaway? Lopata says if dust mite allergy is a problem, treat it. Dust mite immunotherapy “is very effective,” he says. “Just keep an eye on what happens with shellfish.”
What About Finned Fish?
Fish allergies do often begin in childhood and affect about 1 percent of U.S. adults. The major allergen is parvalbumin, a protein that’s also found across species. Whitefish such as cod tend to have higher levels of it than salmon or tuna, Lopata says.
As with the major shellfish allergen, parvalbumin can come in different forms. Cross-reactivity among fish is common but not guaranteed.
In a study of 249 fish-allergic children in Hong Kong, about 40 percent reported they could tolerate at least one kind. Salmon was tolerated by 29 percent, tuna by 9 percent, and halibut by 8 percent. Fewer were able to tolerate tilapia (1.6 percent), catfish (2.4 percent), or carp (4.8 percent), which had higher levels of parvalbumin.
Meantime a trial of 35 fish-allergic children and teens found that 29 percent (10 kids) could tolerate at least one of cod, salmon or mackerel.
“The most common scenario I see are patients who react to salmon but are tolerant of all whitefish, or vice versa. They react to whitefish but they’re tolerant of salmon or tuna,” Mack says. He does have some patients who can tolerate certain types of whitefish, but not others. “That’s trickier to tease out.”
Rethinking Total Avoidance
With seafood allergies, Mack says the concept of total avoidance is being replaced by more nuanced advice. IgE sensitization alone isn’t a reliable predictor of who will react when eating the food, he says.
When advising patients, he pays close attention to their histories. When it’s appropriate, he’ll offer an oral food challenge to determine whether complete avoidance is necessary.
“I have so many families who want to eat certain types of fish,” he says. “So much of those decisions aren’t based on testing. It’s based on what happens when patients eat it.”
It’s also common for families to simply shun all seafood after a child has a reaction to fish or shellfish. This isn’t advised either, Lopata says.
“Fish are vertebrates. They have a spine, like you and me,” Lopata says. “Shellfish don’t have a spine, so their allergen background is completely different.”
Immunotherapy: Limited, But Growing
So far, Palforzia for peanut allergy is the only FDA-approved OIT treatment. (In 2026, it was withdrawn from the market.) Many allergists do offer oral immunotherapy for other foods using grocery products.
However, in 2023 an allergists’ group called the Food Allergy Support Team conducted an online survey of allergists offering OIT. It showed that fewer than 10 percent offered the therapy for shellfish or fish allergy.
In OIT, patients eat a small amount of their allergen, and gradually increase the doses to build tolerance over the course of several months.
OIT for shellfish and fish is challenging. The foods must be cooked and refrigerated, making it inconvenient to have allergen doses away from home. As well, cooking removes water from fish. Mack says that can concentrate the protein and potentially lead to dose variation. With kids, they may also dislike the taste.
Still, some allergists are charting a course. Dr. Dat Tran, an allergist in Houston, developed an OIT product using dehydrated cod and shrimp in solution, packaged in tubes. Called EatFreely OIT, patients can mix the contents of the tube with a smoothie or applesauce.
In a small trial, six patients ages 6 to 18 with confirmed cod or shrimp allergy began OIT starting at a 3 milligrams (mg). Doses increased weekly over 18 weeks.
After reaching 600 mg, children underwent an oral food challenge, then began dosing with actual shrimp or cod for 16 more weeks. Allergic reactions during treatment were common, but reported as mild. About 75 percent experienced itchy mouth, 50 percent experienced lip swelling or hives, and 40 percent had abdominal pain. No one experienced anaphylaxis.
At the end, one child with a cod allergy could eat a full serving; the others stopped at one-half to one fish stick. Among shrimp-allergic children, one could eat a full serving; the other two stopped at one medium shrimp. Taste was the limiting factor for two children, Tran says.
Lopata’s team will offer a bigger test of seafood OIT with their upcoming trial in Singapore trial that aims to enroll 50 to 100 children. In it, shrimp powder will be used to try to desensitize children with shrimp allergy. Enrollment is scheduled to begin by the end of this year.
Xolair and Treating Shellfish Allergies
Working with patients taking Xolair for food allergies, Kim hasn’t had any shellfish or fish-allergic allergic pediatric patients introduce those foods into their diets yet. But he’s optimistic. The first food allergy patients have been on the medication for about a year.
“We’re now starting to have that conversation with patients, ‘Should we do a food challenge to see if it’s working? Do you want to try to eat some?’” Kim says.
In Stage 3 of the OUtMATCH trial, most children with multiple food allergies were able to introduce their allergens into their diet after six months on the drug. However, once they stopped taking it, many could no longer tolerate those foods.
Adults with shellfish or fish allergy might be interested in Xolair, which is given by injection every two or four weeks, especially if turns out they can start eating seafood again, Kim says.
A group of researchers is trying to line up funding to study whether omalizumab combined with OIT can build tolerance in shrimp-allergic adults.
“People are finally shifting their attention to adult food allergies,” Kim says. “They’re recognizing that there’s a lot of people dealing with it and it’s a big unmet need.”
Related Reading:
Shellfish Allergy: Symptoms, Causes and Tricks to Manage
Do Antacids or Alcohol Trigger Shellfish Allergy in Adults?
Allergy Control: How to Defeat Dust Mites, a Big Trigger
