Shellfish Allergy

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Everything you need to know about the shellfish allergy including what it is, what are symptoms of a shellfish allergy, treatment, what to avoid, and how to stay safe. 

The shellfish allergy is a very common and severe allergy that is included in the top 9 allergies of the world. It affects upwards of 2.5% of the global population. 

Shellfish allergies are more than just avoiding eating seafood. There are many by-products from the shellfish industry that have worked their way into many parts of our normal lives, including medications, inks in printers and pens, and coatings on fruits and vegetables. 

A bunch of scallop, clam, and other shelled shellfish. A white hexagon with black text reads, "shellfish allergies 101".

While living with a shellfish allergy can seem overwhelming and difficult, it isn’t insurmountable. 

This article walks you through all aspects of what is a shellfish allergy, symptoms, what to avoid, what you can still enjoy, and how to best manage your shellfish allergy. 

Key takeaways

  1. Shellfish are both crustaceans (crabs, lobsters, etc) and mollusks (oysters, clams, scallops, etc) and you can be allergic to both. 
  2. Mollusks are not always labeled as a shellfish allergy. 
  3. Chitin, a product of shellfish, is being added to medications and nutritional supplements and foods, so avoid chitin and chitosan. 
  4. Shellfish allergies are one of the most severe allergies frequently causing anaphylactic reactions. Talk with your doctor about receiving an Epi Pen if you have a shellfish allergy.  

What is a shellfish allergy

A shellfish allergy is a response of the body’s own immune system thinking that shellfish is a threat. This triggers an autoimmune response known as an allergic reaction. 

Shellfish is a term invented by the fishing industry to distinguish between fish and everything that isn’t fish. Think things with an exoskeleton like lobsters, crabs, and clams. 

Removing the shell does not remove the allergic component of a shellfish allergy. Even if you have someone else peel your shrimp, you can still have a reaction. 

New research is being done to show a connection between shellfish in the sea and insects found on land. There is a protein and sugar molecule found in all of them, making it possible that if you have a shellfish allergy, you could also be allergic to bugs. 

Crustacean, Mollusks, and Shellfish 

Crustaceans include sea creatures like crabs, crayfish, lobsters, prawns, and shrimp. 

Mollusks are sea creatures that are divided into 3 different types: Gastropods (abalone, conch, and snails), Bivalves (clams, mussels, oyster, scallops), and Cephalopods (cuttlefish, squid, octopus). 

A chart showing the types of shellfish, crustaceans, and mollusks.

All of these are shellfish and you have the potential to be allergic to any and all of them.

However! The USFDA only currently classifies crustaceans as shellfish. So if you are allergic to any type of mollusk (such as oysters) you will not be notified on ingredient labeling that the ingredients have a shellfish allergy warming. 

This is why it is so important for you to always read every ingredient label and routinely check the ingredients of your safe products as companies are always changing ingredients. 

Fish Allergies and Shellfish Allergies 

Yes, you can be allergic to both shellfish and fish. You can be allergic to only fish or only shellfish. The allergy to fish is different from a shellfish allergy. 

However, there is a strong possibility that if you have a shellfish allergy you are also allergic to fish. 

Talk with your doctor to test and confirm what you should avoid to stay safe. 

Shellfish Poisoning vs Shellfish Allergy 

Shellfish poisoning is when you eat shellfish that has been contaminated with bacteria or viruses. It can be from raw, poorly cooked, or even from handling contaminated seafood. 

Shellfish poisoning is not the same thing as a shellfish allergy but oftentimes shellfish poisoning can appear as an allergy. 

Since both shellfish allergies and poisoning are so severe, you should always seek medical attention right away if you suspect an allergic reaction or shellfish poisoning. 

Chitin and Shellfish Allergies 

Specifically, the shellfish allergy is a reaction to the proteins and polysaccharide carbohydrates found in shellfish. These are called chitin (pronounced kite-an, rhymes with titan) of the shellfish. 

Chitin is the “goo” that helps to hold the shellfish together. It is found in the exoskeleton and in the soft parts that you eat in a shellfish that protect the inner organs. It is a waxy, impermeable barrier protecting them against bacteria. 

When the chitin is processed and cleaned in manufacturing, it becomes known as chitosan. Both chitin and chitosan are becoming a very popular addition to things such as medications and  nutritional supplements. They are also used as food additives, thickeners, texturizers, emulsifiers, humectants, and stabilizers in confectionary treats (candy), beverages, and other foods. 

Chitin is not affected by heat when cooking. So kitchens that frequently cook fish and shellfish are filled with airborne chitin particles. If you breathe it in, you can have an allergic reaction. 

If you have a shellfish allergy, you should still avoid chitin and chitosan. 

What causes a shellfish allergy? 

Shellfish, like other allergies, is caused by genetics, the environment, or the way the two interact with each other. 

There is currently no known direct cause of shellfish allergies, or any allergies for that matter. Bodies are complicated and the immune system is one of the most complex systems in the body. 

Allergies tend to run in families so if you have an allergy it is likely that someone else in the family has allergies as well. 


If you are allergic to shellfish, you can have one or more of the following reactions. How quickly you react doesn’t always mean you are more or less allergic to shellfish. The reactions can occur minutes or hours after exposure. 

A list of possible reactions includes: 

  • Swelling, itching, or irritation of the mouth, lips, tongue, or throat
  • Asthma attacks
  • Eczema on the skin
  • Hives, itching rash of the skin
  • Nasal congestion
  • Headaches
  • Difficulty breathing
  • Cramping and/or pain of the stomach or bowels
  • Nausea
  • Vomiting
  • Diarrhea
  • Anaphylactic reactions 

Anaphylactic reaction 

For some people, a life threatening reaction known as an anaphylactic reaction may occur after consuming, touching, or smelling shellfish or shellfish by-products. 

If you have an anaphylactic reaction, call 911 or your local emergency number immediately. 

Signs and symptoms include:

  • Swelling and tightening of the throat
  • Difficulty breathing
  • Chest pain or tightness
  • Trouble swallowing 
  • Dizziness or fainting
  • Change of the normal coloring of the skin and in the mucous membranes (inner lips, gums, around the eyes, and the nail beds
    • Light skin, check for signs of a dark blue tint in the mucous membranes
    • Medium skin, check for signs of a gray-green tint in the mucous membranes
    • Dark skin, check for signs of a gray or white tint in the mucous membranes 


A diagnosis begins with sharing your history and suspicions with your doctor. 

An allergist is the most common doctor to diagnose a shellfish allergy. 

There are a few different allergy diagnostic tests to determine if you have an allergy or not. The doctor will know what test is best to determine what exactly you are allergic to. 

  • Skin Prick Tests: Placing a small sample of the suspected allergen in a purified form into the top layer of skin with a small poke (not with a needle). 
  • Blood Tests: Drawing a small sample of blood and sending it to a lab where they will check the blood’s reactivity to the suspected allergens. 
  • Food Challenges: This is the gold standard for diagnosing a food allergy. The suspected food is removed from the diet for 2 to 3 weeks and then reintroduced under the supervision of the doctor. 

Note. It is only safe to do food challenge testing under the supervision of a doctor. Shellfish allergies can be deadly. Do not eat food you know or suspect you are allergic to without guidance and supervision. 

How to manage

The best way to manage your shellfish allergy is to avoid any and all forms of shellfish and shellfish related products to the best of your abilities. 

As with most allergies, the more frequently you are exposed to the allergy, the worse your reaction will be over time. 

If you are still trying to diagnose or have developed new symptoms, a food and life journal can be extremely helpful. These are daily records of what you eat and what you encounter and how you react and feel afterwards. This is helpful to track and see what, if any, patterns emerge. 

For a free food journal, click here! 


The only treatment for a shellfish allergy is to avoid the shellfish as much as you can. 

Antihistamines and other over the counter medications, like Benadryl, can be taken for mild reactions. 

Epi Pens and going to the hospital are necessary for severe reactions. 

Sometimes, for those with severe allergies, wearing a medical bracelet, necklace or having a medical ID card in your wallet is helpful. 

Talk with your doctor to come up with the right allergy plan of action for you. 

Chitosan and Medications 

If you are on medications such as birth control or other fat soluble medications, you should avoid anything that contains chitosan, even if you are not allergic to shellfish. 

The chitosan prevents the medication from being absorbed into the body and thus prevents the medication from working.

Chitosan is now being added to nutritional supplements for weight loss, diabetics, and high cholesterol. There are no studies which have been done to show this is helpful. And with the risk of interference with other medication, I suggest you avoid or at the very least talk with your doctor or pharmacist. 

Do not take it if you are pregnant or breastfeeding, and don’t give it to children. This can interfere with their growth and development. More studies are currently being done on medications and interference with chitosan. 

What to avoid 

Products will not always be labeled if they contain shellfish ingredients. Always read labels carefully.

If you are unsure of a product, contact the manufacturer. Even if you have used a product before, ingredients are always changing. 

Food sources of shellfish:

  • Crustaceans
    • Crab (all forms), lobster (all forms), crayfish, crawfish, prawns, shrimp, krill, scampi, Moreton bay bugs
  • Mollusks
    • Abalone, conch, limpet, snail (escargot), clams, scallops, oysters, cockles, cuttlefish, octopus, squid (calamari), sea cucumbers, mussels, sea urchins,
  • Bouillabaisse 
  • Coatings on fruits and vegetables
    • Any wax coating can be made from shellac, another name for wax from shellfish or bugs 
  • Clam chowder
  • Confectioners Glaze
    • Can be made from shellac, another name for wax from shellfish or bugs 
  • Cuttlefish ink 
  • Fish sauce 
  • Fish stock (some can contain shellfish)
  • Glucosamine 
  • Gumbo 
  • Homebrew Beer or Wine
    • Product used in the clarification of the beer or wine of excess tannins uses a chitosan product 
  • Imitation seafood 
  • Jambalaya
  • Nori and other seaweeds
    • Use caution and talk with your doctor if you can safely eat seaweeds because it comes from the same environment 
  • Paella 
  • Salad dressings
    • Especially Caesar salads
  • Seafood flavoring (crab or clam extract)
  • Shellac
  • Spring rolls 
  • Sushi
  • Sashimi 
  • Surimi 
  • Omega-3 supplements 
  • Oyster sauce
  • Worcestershire sauce 

Non-food sources of shellfish:

  • Bandages
    • Some have chitosan as a means of healing faster 
    • This is especially popular in Europe 
  • Chewing gum, mouth wash, toothpaste
    • Some have chitosan as a means of reducing cavities 
  • Fertilizers
    • Lawn and plants
  • Inks
  • Iodine or Radiocontrast dye
    • While not technically a shellfish allergy, many people can also be allergic to iodine if they have a shellfish allergy 
  • Nutritional supplements
    • Omega-3
    • Fish Oils
    • Glucosamine
    • Glucosamine-Chondroitin
    • Chitosan products made for weight loss, diabetics, and high cholesterol 
  • Pet Foods   
  • Swimming pool clarifier
    • Sea Klear 

What you can eat with a shellfish allergy

Cooking at home is going to be one of the safest options for you and your family as you can ensure that no allergens come into contact with the food you make, so no cross contamination can occur. 

Make sure your diet is filled with simple whole foods such as red meats, poultry, grains, vegetables, fruits, beans, tofu, and lentils. 

Dining out with shellfish allergies 

The main challenge when being allergic to shellfish is going to be dining out in restaurants as many people have a reaction to even the smell of shellfish. The allergens can float on the air and cause severe allergic reactions. 

The best way to avoid (or at least try to avoid) getting sick at restaurants is to research ahead of time and only eat at places that do not serve shellfish. 

Most restaurants post their menus online, giving you a change to figure out if this is a safe option to eat. Even if the menu says “allergy friendly” you should still research and contact the restaurant because it is really difficult to ensure a kitchen can safely prepare food when you have severe allergies. 

For shellfish allergies in particular it is important to ask the restaurant about their frying process as they often use the same fryer for french fries, fried calamari, and fried chicken. You will need to ask if there are separate fryers for fish/shellfish as you don’t want to have the risk of cross contamination via the oil. 

Tip! Food items labeled kosher will not contain any shellfish products. 

Insects and Shellfish Allergies 

Insects are in the same phylum (animal kingdom) as shellfish. 

Just like shellfish, insects all have exoskeletons and are filled with chitin. Studies are being done right now to connect insects (kind of like land shellfish) with shellfish (kind of like sea insects). 

A chart showing the connection of the animal kingdom of Arthropods connecting insects to crustaceans and mollusks, aka, shellfish.

If you have a shellfish allergy, it is suggested that you avoid insects as much as possible in things like foods and from being bitten by them. 

The insects that are most commonly associated with a shellfish allergy include:

  • Ants
  • Beetles 
  • Bees 
  • Cockroaches 
  • Crickets 
  • House Dust Mites 
  • Grasshoppers 
  • Scorpions 
  • Spiders
  • Wasps 

You want to avoid being stung as the stinger is made of chitin, so you are having a touch reaction to the shellfish allergy component of the bug. 

If you are severely allergic to shellfish, you should use extreme caution for keeping a scorpion or spider/tarantula as a pet. I also would use caution when keeping reptiles as a pet as they regularly eat insects. 

More allergy articles to explore

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