Shellfish allergy in babies

Shellfish allergy: the basics

Shellfish allergy happens when the immune system overreacts to proteins in shellfish. ACAAI says shellfish is among the most common food allergens, and the NHS lists shellfish such as prawns, crab and lobster among the most common allergic foods.

Shellfish come in two groups:

• crustaceans: shrimp (prawns), crab and lobster
• mollusks: clams, mussels, oysters, scallops and squid

ACAAI says crustaceans cause the most reactions, and many people with shellfish allergy can eat mollusks without a problem. But that’s not true for everyone, so ACAAI says anyone who has reacted to shellfish should see an allergist before eating any other kind.

Shellfish allergy most often starts in adulthood, but it can affect children (ACAAI). Like peanut, tree nut and fish allergy, it typically lasts for life (ACAAI).

Shellfish and fish are separate allergies

ACAAI says a shellfish allergy is different from a fish allergy: people allergic to shellfish don’t necessarily have to avoid fish, and the reverse is also true. A child can be allergic to both. If your baby reacts to one, ask your allergist before offering the other. See fish allergy.

Introducing shellfish

Shellfish can go in with your baby’s other first foods, from around 6 months. The CDC lists shellfish among the potentially allergenic foods to introduce when you introduce other foods, and the NHS lists it among the foods to introduce one at a time from around 6 months. The AAP lists shellfish with egg, peanut and the other allergens to offer once your baby has managed a few lower-risk first foods.

Never raw or lightly cooked. The NHS says not to serve shellfish raw or lightly cooked to babies, because of the risk of food poisoning. The FDA says shrimp, crab and lobster are cooked when the flesh is firm, pearly and opaque, or at 145°F (63°C). Good first forms:

• cooked, peeled shrimp, minced very finely and stirred into mashed potato or rice
• fully cooked crab meat, picked over for shell and finely shredded
• minced shellfish shaped into soft, finger-sized cakes

Offer the first taste on a day your baby is well, at home, when you can watch them for a couple of hours afterward. Start with a small amount, and if there’s no reaction, build up over the next few servings. Then keep it in your baby’s diet: see keeping allergens in the diet.

Talk to your doctor first if your baby has severe eczema, an egg allergy, or has already reacted to a food (AAP). Ask how and when to introduce shellfish and the other allergens, not about putting them off.

Signs of shellfish allergy

Reactions usually start within minutes of eating, but can take up to 2 hours (NHS).

Mild to moderate (ACAAI, NHS):

• hives or a red, itchy rash
• mild puffiness of the face or around the eyes
• vomiting once, tummy pain or diarrhea
• sneezing, or a stuffy or runny nose

If it’s only one of these, stop offering shellfish, stay with your baby and watch them closely for the next couple of hours, and call your pediatrician before you offer any shellfish again. After shellfish, vomiting or diarrhea can also be shellfish poisoning (see below), so call your pediatrician or GP the same day rather than waiting. If signs show up in more than one part of the body at once, treat it as anaphylaxis (below).

Signs of anaphylaxis are trouble breathing, wheezing or a cough that won’t stop, swelling of the tongue or throat, lips or mouth that suddenly swell, a hoarse cry, turning pale or floppy, becoming very sleepy or unresponsive, or signs in more than one part of the body at once. If you see any of these and your baby has an epinephrine (adrenaline) auto-injector, use it right away, then call for an ambulance. Call 911.Call 999.Call your local emergency number (such as 112 in Europe or 000 in Australia). If you don’t have an auto-injector, call straight away. Keep your baby lying down, never standing or walking (on their side if they’re vomiting, head and shoulders a little raised if breathing is hard), and go to hospital even if they seem better. See signs of anaphylaxis.

Shellfish poisoning can look similar

Shellfish can carry toxins from algae blooms (“red tide”) that cooking doesn’t destroy. The CDC names mussels, oysters, clams, scallops, crab, shrimp and lobster. Symptoms usually start 30 to 60 minutes after eating and can include numbness and tingling, vomiting, diarrhea and confusion, and severe cases can be fatal. For vomiting, diarrhea or tingling after shellfish, get medical care right away and say what your child ate. Call 911Call 999Call your local emergency number (such as 112 in Europe or 000 in Australia) if your child seems confused, becomes floppy or very sleepy, or has any trouble breathing. Buy shellfish from a shop or supplier you trust: the FDA says live shellfish should carry a tag showing it was harvested under national safety controls.

Delayed, repeated vomiting a few hours after eating, without hives, can also be FPIES, a different kind of food allergy. If your baby vomits once or twice a few hours after shellfish and is alert and like themselves, call your pediatrician or GP. Call 911 or go to the emergency room if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake.Call 999 or go to A&E if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake.Call your local emergency number (such as 112 in Europe or 000 in Australia) or go to the emergency department if your baby is vomiting again and again, or is pale, floppy, very sleepy or hard to wake. See FPIES.

How shellfish allergy is diagnosed

Your doctor or an allergist will ask what your baby ate, how much, how long before symptoms started, and what they were. They may arrange a skin prick test or a blood test for IgE. ACAAI says neither test is conclusive on its own. If the results aren’t clear, the allergist may suggest an oral food challenge, under strict supervision with emergency medicine on hand. Don’t try a challenge at home, and don’t offer a different shellfish to “test” it.

Living with shellfish allergy

Avoid shellfish as your allergist advises, and read labels every time.

• US labels must name crustacean shellfish by type, such as “shrimp” or “crab” (FDA). Mollusks don’t count as a major allergen in the US, so clams, mussels, oysters and scallops may not be flagged in a “Contains” statement (FDA, ACAAI). Check the full ingredient list, and ask the maker if you’re not sure.
• UK labels list crustaceans and molluscs as two separate allergens, emphasized in the ingredients list, for example in bold (GOV.UK).
• Where shellfish turns up. ACAAI says shellfish is rarely hidden, but it can be in fish stock, seafood flavoring (such as crab extract), sushi and surimi.
• Cooking steam and cross-contact. ACAAI says some people react just from being near shellfish being cooked, and that shellfish are often stored together in markets and restaurants, so tell anyone who cooks for your child.

Keep introducing the other common allergens as your doctor advises.

When to see a doctor

Call your pediatrician or GP if:

• your baby has had any reaction to shellfish, even a mild one
• your child has a shellfish allergy and you want to know about fish, mollusks or other allergens

Don’t cut major foods out of your child’s diet on your own: the NHS says to talk to your health visitor or GP, who may refer you to a dietitian.

Where US and UK advice differs

• Which shellfish are labeled. In the US, only crustacean shellfish (shrimp, crab, lobster) are a major allergen; mollusks are not (FDA). In the UK, crustaceans and molluscs are both among the 14 allergens food businesses must tell you about (GOV.UK).
• Who should check first. The NHS asks you to talk to your GP or health visitor before introducing allergens if your baby has eczema or a food allergy, or there’s a family history of food allergies, eczema, asthma or hay fever. US guidance singles out severe eczema and egg or other food allergy.

For the other allergens, see how to introduce allergens and the safe first form of each one.