Shellfish Allergy 101: Everything To Know, Including What Foods To Avoid

Keep Clam! What to Know About Shellfish Allergies, Like What You Can (& Can’t) Eat

March 4, 2020 Updated July 28, 2021

allergies-shellfish-explainer-fi (1)
Toa Heftiba/Unsplash

Shellfish is one of those love-it-or-hate-it kinds of foods: It’s either something you gravitate towards on any menu or avoid like the plague. Sort of like eggs. But for some people, steering clear of shellfish is more than a matter of taste — thanks to having a shellfish allergy, it could literally make them sick (and, in some super-serious cases, cause potentially life-threatening anaphylaxis). As it turns out, a shellfish allergy is one of the most common food allergies, affecting an estimated seven million Americans.

Like seasonal allergies, shellfish allergies are not limited to a single age group. However, they do impact adults more than babies, toddlers, and older kids. And let’s face it: Regardless of the person’s age with a shellfish allergy, it can be pretty scary. Fortunately, we can arm ourselves with the knowledge we need to take the best possible care of ourselves and our children. Knowing exactly what to look for, what to do when an allergic reaction happens, and when to do these things turns fear into action.

So, consider this a one-stop shop for all information pertaining to shellfish allergies. We picked the brains of medical professionals and allergy specialists to bring you the full 4-1-1 so that you have one less source of stress. Here’s what to know about shellfish allergies, including the classic symptoms, the foods to avoid, and a few myths that need to be dispelled.

RELATED: Soy Allergies — A Full Guide To Symptoms, Treatment, And Management

What is a shellfish allergy?

A food allergy is a medical condition in which exposure to certain foods creates an abnormal (and potentially harmful) immune response. That response, which is known as an allergic reaction, happens because the immune system launches an attack on proteins in the food the body would normally find harmless.

With a shellfish allergy specifically, the protein — or allergen — that triggers the response is marine animals in the shellfish category. This includes a reaction to crustaceans and mollusks such as:

  • crab
  • lobster
  • oysters
  • scallops
  • shrimp
  • squid
  • and more

What are the symptoms of a shellfish allergy in a baby, toddler, child, teen, and adult?

According to Dr. Kathleen Dass, the owner and residing allergist-immunologist at Michigan Allergy, Asthma & Immunology Center, symptoms of a shellfish allergy can vary from person to person, and case to case, and are the same regardless of a person’s age. “Symptoms of a shellfish allergy can vary from mild to severe and life-threatening,” she told Scary Mommy. Per Dass, these symptoms include:

  • anaphylaxis
  • hives
  • nausea
  • vomiting
  • dizziness
  • trouble breathing
  • swelling of the face/mouth/tongue/throat
  • trouble swallowing
  • losing consciousness
  • increased heart rate
  • drops in blood pressure

Where age does become a factor is communication. “These symptoms can present the same whether it is a baby, toddler, child, or teen. Since babies cannot tell you they are having an allergic reaction, you can also look for your baby to become fussier and turning blue. Children can also develop a non-IgE mediated reaction called FPIES (Food Protein-Induced Enterocolitis), which presents with gastrointestinal symptoms like nausea, abdominal pain, and protracted vomiting and/or diarrhea,” Dass explained.

How long does a shellfish allergy reaction take to develop?

Symptoms of a shellfish allergy typically present anywhere from immediately after eating shellfish to within two hours. However, a non-IgE mediated reaction can happen one to six hours after ingestion. Also good to know? Shellfish allergies can develop out of the blue in children who’ve eaten shellfish with no problem in the past.

What’s the difference between a shellfish allergy and a seafood allergy?

It’s possible you’ll hear people use the terms “shellfish allergy” and “seafood allergy” interchangeably. It’s important to understand there is, in fact, a distinction between the two. Nutritionist Lisa Richards — author of The Candida Diet and contributor to Today, US News, Women’s Health, and more — broke it down for Scary Mommy.

“It is a common misunderstanding that a fish allergy and a shellfish allergy are one and the same, but this is a dangerous and inaccurate assumption. While fish (like tuna or salmon) and shellfish (like shrimp or lobster) are both categorized as seafood, they differ biologically. You can be allergic to both types, but they are not the same thing. An allergic reaction to shellfish is generally more severe and includes wheezing, hives, swelling, vomiting, anaphylaxis, and more. A fish allergy can result in severe symptoms, but anaphylaxis is rare. Headaches, nausea, and runny nose are the most common side effects of a fish allergy.”

This means fish will not cause an allergic reaction in a person who has a shellfish allergy unless they also have a fish allergy. This can get muddled because fish is often prepared in the same space as shellfish. So, shellfish proteins can find their way into non-shellfish foods that were prepared alongside shellfish, leading to confusion over what caused the reaction.

How do you test for a shellfish allergy?

If you have any inkling you or your child might be allergic to shellfish, schedule an appointment with an allergist ASAP. “First, an allergist will take a history to establish a suspicion for a shellfish allergy. Then, skin-prick testing will be performed to shrimp, crab, and lobster. We may also check IgE levels to shrimp, crab, and lobster. An IgE tests for an allergy, whereas IgG tests for any previous exposure. This is why allergists will only test for the IgE in the blood,” said Dass.

If an allergist suspects the likelihood of a true allergy is low, they might recommend an oral food challenge. An oral food challenge occurs when a small amount of the allergen, in this case, shellfish, is given to the patient. The doses are incrementally increased until a specified number is reached. If a patient passes the food challenge, they are deemed as not allergic.

Of course, it goes without saying you should never attempt the food challenge without first speaking to an allergist to rule out the possibility of a serious shellfish allergy.

What is considered shellfish and what foods should a person with a seafood allergy avoid?

Once you or your child test positive for a seafood allergy, your doctor will give you all sorts of informative pamphlets and literature regarding what’s safe to consume. It goes without saying this includes shellfish. Interestingly, some people with shellfish allergies will react to crustaceans and not mollusks or vice versa — confirm with a healthcare provider whether you should stay away from all shellfish or certain types.

As a general rule of thumb, though, a person with shellfish allergies should avoid:

  • abalone
  • anchovies (while not shellfish, they contain a similar protein)
  • barnacle
  • calcium supplements made from coral
  • clams
  • cockle, periwinkle, and sea urchin
  • crab; crawfish/crayfish, ecrevisse, krill
  • cuttlefish
  • limpet (lapas and opihi)
  • lobster, langouste, langoustine, Moreton bay bugs, scampi, coral, tomalley
  • mollusks
  • mussels
  • oysters
  • octopus and squid/calamari
  • scallops
  • sea cucumber (beche-de-mer)
  • shrimp, prawns, crevette
  • snails
  • whelks

Basically, you’ll need to become a pro at reading food labels and just being super-vigilant about where your food comes from. Any food made in a seafood restaurant could be cross-contaminated with shellfish. Some people can have an allergic reaction simply from being around cooking odors, from touching shellfish, or from being exposed to shellfish steam (the shellfish protein is released in the steam during cooking).

What other ingredients should you avoid if you have a shellfish allergy?

Be mindful to eschew certain products or foods if you see the following words or ingredients listed on a label or menu, as it may mean shellfish protein is present:

  • bouillabaisse
  • cuttlefish ink
  • fish stock
  • glucosamine
  • seafood flavoring
  • surimi
  • paella
  • some types of sushi contain
  • tapenade
  • Worchestershire sauce

Are there any non-food items to watch out for?

Yep, you guessed right. It isn’t just shellfish that could potentially trigger a seafood allergy. In addition to steam and cooking odors, most shellfish-allergic people are sensitive to dust mite and cockroach allergies. You can also check out the resources on the Food Allergy Research and Education website for more information on both ingestible and non-ingestible seafood-related allergens.

Are shellfish allergies genetic?

If you or your partner have a shellfish allergy, you may be wondering what the risk factors are for developing a shellfish allergic reaction. Why did you end up with one? And, more pointedly, does you having a shellfish allergy make it more likely your child will develop one? Well, yes and no. Elaborated Dass, “Shellfish allergies specifically have not yet been shown to be genetic. However, if allergies of any kind exist in your family, then you are at increased risk for food allergy.”

Do shellfish allergies ever go away?

Listen, anything is possible. Miracles do happen. You know the spiel. Having said that, allergies to peanuts, tree nuts, fish, and shellfish are generally lifelong. “It is possible to outgrow a food allergy, though there are certain foods you are more likely to outgrow — such as milk or egg,” said Dass. “Shellfish allergy is less likely to be outgrown, but this can vary by person.”

That being said, a shellfish allergy is actually less common in children, most recently reported at 0.5-percent in kids versus 2.5-percent in adults, per Dass. Still, if your child does happen to be part of that percentage, you’ll have to be proactive. There isn’t currently a cure for food allergies, so you simply have to avoid triggers and learn to recognize and treat reaction symptoms.

On the plus side, clinical trials are happening at this very moment that center on food allergy therapies. None have been approved for general use yet, but there’s certainly hope treatment options will be available in the future.

Can you suddenly become allergic to shellfish? 

In short, yes. People can develop shellfish allergies at any age, though it’s most common in adults — specifically, women, according to the Mayo Clinic. This means that some people can spend decades chowing down on bivalves with no problems whatsoever, then, as an adult, suddenly have an allergic reaction.

What are some common shellfish allergy myths (and the reality)? 

There are plenty of myths floating around about shellfish allergies, but not all are based in reality. For instance, they are not caused by iodine. And, on the flip side, you’re not allergic to iodine solely because you are allergic to shellfish. While shellfish does contain iodine, that’s not what triggers an allergy, according to Everyday Health.

Along the same lines, it’s perfectly safe for someone with a shellfish allergy to get a CT scan, including the contrast dye used prior to the procedure. The materials used in the contrast dye do not contain any of the allergens found in shellfish. While some people are, in fact, allergic to the contrast dye, it has nothing to do with shellfish.

What should you know about a shellfish allergy and COVID vaccine?

During the beginning of the COVID-19 vaccine rollout, there was a lot of concern over allergic reactions to the inoculation, including questions regarding whether people with common food allergies (like to shellfish) should receive the vaccine. Now, more than six months and millions of injections later, we have a much clearer picture of a potential threat — or, more accurately, the lack thereof.

“What the science tells us is that COVID-19 vaccines are safe for most people with allergies, including those who have allergies to eggs, peanuts, shellfish, latex, penicillin, animals, and other common triggers,” says Dr. Stephen Scranton, a board-certified allergist with the Mid-Atlantic Permanente Medical Group. He goes on to clarify that the risk of a potentially life-threatening allergic reaction to the COVID-19 vaccines is minuscule and currently thought to be no more frequent than about 1 in 200,000.

Are there shellfish allergy treatments you can try at home?

If you have an allergic reaction to shellfish, seek emergency treatment right away. However, sometimes, antihistamines like Benadryl or Claritin can reduce itchiness and rashes if the reaction is mild. A more severe reaction may cause anaphylaxis, which is deadly and requires an EpiPen. Treatment depends on the severity of the reaction, but it’s always safer to head to the emergency room.