Symptoms of a food allergy: hives or itchy skin, sneezing, swelling, anaphylaxis

Shellfish allergy symptoms and signs

Medically reviewed on August 1, 2022 by Jordan Stachel, MS, RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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If you’ve ever experienced a reaction to a food you’ve eaten, you’re certainly not the only one. Between 6 to 8 percent of people may have an allergy to a specific food item. [1] People can have allergies to many foods, including peanuts, eggs, soy, wheat—and yes, even shellfish.

Shellfish allergies are one of the few allergies more common in adults than in children. [2] In fact, as many as 1 in every 100 adults might have some degree of shellfish allergy.

But what does an allergy to shellfish look like, and how can you find out if you’re allergic?

This guide will walk you through everything you need to know about shellfish allergies, how to know if you have one, and what allergy treatment options are available.

What causes allergic reactions to shellfish?

Food allergies occur when your immune system overreacts to a specific type of food. But regardless of what food you’re allergic to, the reaction process for most food-related allergic reactions is similar.

For those with shellfish allergies, it usually involves the following: [3]

  1. Your body is exposed to seafood or a type of shellfish
  2. The tropomyosin protein in the shellfish binds to antibodies produced by your immune system
  3. The shellfish protein then triggers your immune system to produce more antibodies
  4. Your immune system also releases histamine, which is responsible for some symptoms
  5. You experience allergic reaction symptoms due to your immune response

The symptoms you experience can vary in severity depending on how serious your shellfish allergy is. The severity of your symptoms also depends on your immune system. Everyone’s immune system reacts to stimuli differently.

Which shellfish species can cause allergic reactions?

Any species of shellfish can cause allergic reactions in some individuals. [4] These can include crustaceans, such as:

  • Shrimp
  • Crab
  • Lobster
  • Prawns

The mollusk, or bivalve, is another group of shellfish that can cause an allergic reaction. Mollusk shellfish include:

  • Mussels
  • Clams
  • Oysters
  • Squid
  • Octopus
  • Snails
  • Scallops
  • Abalone

Of these two groups, most people experience more severe reactions to shellfish in the crustacean group. Some people who are allergic to crustaceans can eat mollusk without any problems.

What is the most common shellfish allergy?

Both children and adults are more likely to be allergic to crustaceans than they are mollusks. But when it comes to the common crustaceans, shrimp is the one most likely to trigger an allergic reaction.

It’s also fairly common to have the most severe reaction to shrimp, but still have a mild reaction to other members of the crustacean family. [4]

That being said, unless your healthcare provider tells you otherwise, if you’re allergic to shrimp, you should avoid all crustaceans.

What are the symptoms and signs of a shellfish allergy?

Those who suffer from shellfish allergies may experience several different symptoms, or even several at once. Some common shellfish allergy symptoms can include: [3]

  • Vomiting, diarrhea, stomach pain, bloating, and gas
  • Hives on the body
  • Dizziness and confusion
  • Tingling or swelling in the lips and tongue
  • Itching or numbness around the throat or mouth
  • Feeling like you can’t breath
  • Repetitive, non-productive cough
  • Pale skin

Some people who have a severe shellfish allergy could experience anaphylaxis. Anaphylaxis occurs when your immune system goes into serious overdrive and releases a rush of chemicals. This onslaught of chemicals can cause you to go into shock as your blood pressure drops and you have difficulty breathing.

Signs of anaphylaxis include:

  • Sudden skin rash
  • Difficulty breathing
  • Very weak or rapid pulse
  • Nausea and vomiting

Anaphylaxis can be life-threatening. If you think you could be having an anaphylactic reaction, seek emergency medical attention immediately.

Are there different levels of severity of shellfish allergies?

If you have a shellfish allergy, your reaction might not necessarily look the same as a friend or family member who also does. People can have very different symptoms. Furthermore, severity of the symptom that characterize their shellfish allergy.

Some people have a mild response to shellfish exposure that can be treated with an antihistamine or other allergy medication. Others can have a severe, life-threatening allergic reaction that requires immediate treatment at a healthcare facility. [3]

It’s also possible that your allergy can worsen over time, so you could have a more serious reaction even if you’ve only experienced mild reactions in the past. This is why it’s important to avoid shellfish if you have a known allergy—even if it’s just a mild one.

It’s also possible that your allergy can worsen over time, so you could have a more serious reaction even if you’ve only experienced mild reactions in the past. This is why it’s important to avoid shellfish if you have a known allergy—even if it’s just a mild one.

When can you develop an allergy to shellfish?

One of the unique characteristics of shellfish allergies is that they don’t always develop in childhood. Some people can eat shellfish without any problems when they are children, only to begin having trouble after they reach adulthood.

In fact, nearly 60% of those diagnosed with a shellfish allergy didn’t experience their first symptom until they were an adult. [3]

There could be several reasons for this, including:

  • Hormonal changes as we grow older
  • Genetic and environmental factors
  • Viral or bacterial factors that change your body’s response

Researchers aren’t certain of the cause of adult-onset shellfish allergies. However, if you experience symptoms of an allergic reaction after you consume shellfish, you should take proper precautions and consider taking an allergy test.

How long does it take to have an allergic reaction to shellfish?

An allergic reaction to shellfish typically doesn’t take too long to develop. You might experience some symptoms within minutes of coming into contact with the shellfish allergen, whether it’s by touching shellfish or eating it. Other symptoms can take up to an hour to show up. [5] But if you experience severe symptoms immediately after consuming shellfish, you should seek medical attention right away.

How are shellfish allergies diagnosed?

How do I know if I’m having an allergic reaction to shellfish? Diagnosing any food allergies can be tricky and shellfish is no different. Everyone can experience varying symptoms and severity of symptoms.

In addition, some people only experience an allergic reaction when they actually eat shellfish, while others might react when they come into contact with it—either by touch or by being near someone cooking shellfish.

These complications mean the process of confirming a shellfish allergy can take several steps. Some of these may include: [6]

  • A questionnaire – One of the first things you’ll be asked to do if you think you may have an allergy to a specific food is complete a questionnaire. The questionnaire will establish what you ate, when you ate it, how much you consumed, what your reactions were, the severity of the reaction, and more. You may even be asked to keep a food diary for several days to mark down other potential causes of your allergic reactions.
  • A skin prick test – A skin prick test involves placing a small drop of liquid containing the potential food allergen on your skin (in this case, the shellfish allergen). Then, a small needle pricks the skin so that a tiny bit of the food allergen-containing liquid can seep into the skin. If you have an allergy to the substance, your skin will form a small red bump. This type of allergy testing gives you quick results—often within 30 minutes or fewer.
  • A blood test – Blood tests are used as an alternative or in conjunction with skin prick tests. A small blood sample is drawn and then analyzed for a specific antibody. The presence of that antibody indicates the potential for an allergic reaction. This allergy testing takes a little longer to get results—typically a week or two. However, one advantage of this type of test is that you can do it at home using an at-home allergy test kit.

Depending on your symptoms and the severity of your reaction, a healthcare professional might use one or all three of these methods to determine if you’re likely to be allergic to shellfish.

What treatments help allergic reactions to shellfish?

Like with many food allergies, there isn’t a magic pill or other remedy for shellfish allergies. The best way to protect yourself from experiencing an allergic reaction is to avoid shellfish entirely.

There are a few sneaky places where shellfish can appear in foods, so you’ll want to make sure that you diligently check the food products that you buy. Some of these products might include:

  • Sauces
  • Broths
  • Seasoning mixes
  • Sushi

Restaurants may also prepare foods that don’t contain shellfish near those that do. Depending on the severity of your allergy, this may also cause you to have a reaction.

If you do come into contact with shellfish and experience an allergic reaction, there are a few types of treatments that might help control the response or, in life-threatening situations, save your life. [6] These might include:

  • An EpiPen – If you have a severe food allergy, your doctor might prescribe an epinephrine injector, more commonly known as an EpiPen. This can be a life-saver if you have a severe allergic reaction and go into anaphylactic shock. Even if you can use your EpiPen and the reaction starts to calm down, you should still call an ambulance to be on the safe side.
  • Over-the-counter or prescription medications – For those who suffer from more moderate allergies to shellfish, an over-the-counter or prescription allergy medication might be able to help control the reaction. Antihistamines and corticosteroids are both commonly prescribed to treat mild allergy symptoms.

Keep tabs on your food allergies with Everlywell

Food allergies can take you by surprise—especially if you’ve been able to enjoy a type of food in the past but later find out that you’re allergic. Fortunately, there are easy ways to gain awareness of your reactions to foods and know which ones to avoid going forward.

If you’ve experienced some discomfort or allergy symptoms after eating certain foods recently, the Everlywell Food Allergy Test might help you get some answers to your health concerns.

You can take this simple, finger-prick test in the comfort of your own home. It screens for reactivity to common food allergens, including shrimp. If your test indicates that you might have an allergy, one of our qualified nurses will contact you to outline your next steps.

Find the health and wellness answers you’ve been seeking with Everlywell.

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  1. Update on Food Allergy. PubMed. URL. Accessed August 1, 2022.
  2. Shellfish Allergy. Mayo Clinic. URL. Accessed August 1, 2022.
  3. Shellfish Food Allergy Research and Education. . URL. Accessed August 1, 2022.
  4. Shellfish Allergy. PubMed. URL. Accessed August 1, 2022.
  5. About Shellfish and FIsh Allergies. BetterHealth.vic. URL. Accessed August 1, 2022.
  6. Shellfish. American College of Allergy, Asthma, & Immunology. URL. Accessed August 1, 2022.
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