Shellfish Allergy

Shellfish allergies are the most common food allergies in adults and a common allergy in children as well (1). It is incredibly rare for someone to outgrow a shellfish allergy. The most common shellfish allergy is an allergy to shrimp. Similar to fish allergy, many people (about 60%) will not experience their first reaction until they are adults (1).

Shellfish are broken down into 2 groups: crustaceans and mollusks/bivalves. Crustaceans are foods such as shrimp, prawns, crab and lobster. Mollusks/bivalves are foods such as clams, mussels, oysters, octopus, squid, abalone, and snail. Crustacean allergy is more common than a mollusk allergy.

Finned fish are different from shellfish. Being allergic to one doesn’t mean that you’ll be allergic to the other. There does tend to be a lot of cross contact between the two in places such as restaurants, so if you are allergic to one, you should be careful where the other is cooked.

How to Introduce Shellfish

As with other allergens, introduce shellfish as the only new food that day. If you are looking for a more comprehensive guide to introducing allergens, then check out my Allergy Introduction Handbook. Please note that some of these suggestions include other allergens (indicated with a *).

• Shrimp broth
• Crab cake*
• Jumbo shrimp (baby will just suck on the shrimp, not eat it)
• Crab cooked soft
• Pureed shrimp and sweet potato

Diagnosis

The gold standard for the diagnosis of a food allergy is an oral challenge. While scary, it’s actually an easy test to perform: if the child eats the allergen, do they consistently produce a reaction? If so, they are allergic. Then, to confirm a diagnosis, a doctor may use a blood test or skin prick test. A medical professional should always make the diagnosis as a self-diagnosis can lead to unnecessary restriction.

How to Avoid Shellfish

It may not be as simple as just not eating shellfish. Shellfish can come into contact with other foods during processing. There can be cross-contact in the kitchen if the cook touches shellfish or shellfish product and then cooks another dish.

It’s very important to always check food labels. Companies need to list crustacean shellfish clearly on the ingredients list in plain language or under the label in a statement that reads “Contains shellfish.” Packages must identify the specific type of crustacean shellfish (saying crab or shrimp for example). Mollusks are not required to be labeled.

Many people who are allergic to one kind of shellfish are allergic to other types as well. Doctors may recommend to avoid all types of shellfish.

Places to Check

Always ask about ingredients in foods that you did not make yourself. When eating at a restaurant, there is always a risk of cross-contact, so it is important to make it very clear that there is an allergy.

You may want to completely avoid seafood restaurants. There is a high risk for cross-contact. You can also avoid fish markets and places where you would touch shellfish. Shellfish protein can be in the steam, so avoid places where shellfish is being cooked.

Types of Crustacean Shellfish

Avoid these foods with a shellfish allergy:

• Barnacle
• Crab
• Crawfish (crawdad, crayfish)
• Krill
• Lobster
• Prawns
• Scampi
• Shrimp

Mollusks

You may be advised to avoid mollusks as well, although mollusks are not required to be labeled.

• Abalone
• Clams
• Cockle
• Cuttlefish
• Limpet
• Mussels
• Octopus
• Oysters
• Periwinkle
• Sea cucumber
• Sea urchin
• Scallops
• Snails (escargot)
• Squid (calamari)
• Whelk

Unexpected Shellfish Sources

Definitely check labels, because companies make products differently, but foods such as bouillabaisse, cuttlefish ink, glucosamine, fish stock, seafood flavoring, fish stock, fish sauce, and surimi may contain shellfish.

Is iodine or carrageenan a concern?

Iodine is not what triggers an allergy in a shellfish allergy. Assuming you do not also have an iodine allergy, it is safe for you to use iodine or radiocontrast material. Carrageenan is also safe. It is a red marine algae that is used as an emulsifier, stabilizer, and thickener (1). It is not made from shellfish.

Shellfish Allergy Symptoms

A reaction to shellfish can occur through the air if shellfish is being cooked and you breathe in the steam. Most reactions occur from eating shellfish or handling shellfish and then touching your eyes or mouth.

Although reactions can range from mild to severe, it is usually recommended for all kids with shellfish allergies to have an epi-pen with them at all times. Epinephrine is used to treat anaphylaxis, a severe reaction to allergies.

This is not intended as medical advice. If you have any concerns about your child, reach out to your physician. If your child is having multiple symptoms or severe symptoms, call 911.

	Mild	Severe
Skin	mild rash, some hives	widespread rash, hives all over the body
Face	itchy mouth, runny nose, sneezing	lip swelling, tongue swelling
Gastrointestinal	nausea	vomiting, diarrhea
Airway	none	coughing, wheezing, trouble breathing