Patient education: Seafood allergy (The Basics)

What is a seafood allergy? — 

A food allergy is when the immune system acts like a certain food is harmful to the body. The immune system is the body's infection-fighting system.

Some people are allergic to seafood. There are 2 types of seafood allergies:

●Fish allergy – Examples include salmon, tuna, sole, and catfish.

●Shellfish allergy – There are 2 kinds of shellfish:

•Crustaceans – Examples include shrimp, crab, and lobster.

•Mollusks – Examples include clams, oysters, and mussels.

People can be allergic to fish, shellfish, or both. Seafood allergy is more common in adults.

Most often, allergic reactions happen from eating the food or something that contains the food. Touching the food can also cause a skin reaction.

What are the symptoms of an allergic reaction? — 

With "classic" food allergies, also called "IgE-mediated" food allergies, common symptoms include:

●Hives, which are raised or puffy areas of skin that are itchy (picture 1)

●Flushing

●Swelling, especially of the face, eyelids, or lips (picture 2 and picture 3)

●Trouble breathing, noisy breathing (wheezing), or coughing

●Nausea, vomiting, or diarrhea

●Feeling dizzy or passing out

●Looking sick, seeming sleepier than usual, or not acting normally (in babies and young children)

The above symptoms often start quickly, usually minutes to 1 hour after eating the food.

When an allergic reaction is more severe, it is called "anaphylaxis." This can make you very sick, very quickly. If not treated, it can lead to death. But this is rare.

Symptoms can differ from person to person. Also, a person can have different symptoms each time they have an allergic reaction.

There are other types of food allergies that cause different symptoms. These are called "non-IgE-mediated" food allergies. This includes food protein-induced enterocolitis syndrome ("FPIES"), which is a condition that is usually caused by milk (for example, in baby formula). It can also be caused by seafood. When FPIES is caused by seafood, it mostly affects adults after eating mollusks. It causes nausea, belly pain, and severe vomiting or diarrhea. The symptoms usually start a few hours after eating and are very similar to food poisoning. Sometimes, people think they have food poisoning when they really have FPIES.

Is there a test for a seafood allergy? — 

Yes. Your doctor or nurse will ask about your symptoms. You might need to see an allergy specialist, called an "allergist."

Your doctor can order tests such as:

●Blood test – This looks for proteins the body makes when having an allergic response to seafood. These proteins are called "IgE antibodies."

●Skin test – This involves pricking your skin with a device that contains a tiny amount of the seafood. If you get a red, itchy bump, like a mosquito bite, it means you are allergic to that kind of seafood.

If the doctor still cannot tell if you or your child has a seafood allergy, they might order a test called an "oral food challenge." This involves eating a small serving of the food and gradually eating more to see if it causes symptoms. For safety reasons, this is only done in a doctor's office or hospital.

Some people with a seafood allergy can eat seafood that is canned. In some situations, doctors will do a food challenge with canned seafood, like tuna. This helps them figure out what types of seafood a person is likely to react to.

Can a seafood allergy be cured? — 

As of now, there is no cure for a seafood allergy.

How are allergic reactions treated? — 

Severe allergic reactions are treated with medicine called epinephrine. Ambulance crews and doctors can give it. People who had anaphylaxis before often get a prescription for epinephrine. It comes in 2 forms:

●A device called an "autoinjector" (sample brand names: Auvi-Q, EpiPen), which is a shot you can give yourself (figure 1)

●A spray that goes in the nose (brand name: neffy) (figure 2)

If your doctor prescribes epinephrine:

●They will show you how to use it.

●They will give you instructions for when to use it.

●Keep it with you at all times. Most doctors recommend carrying 2 doses in case you need a second dose. You might need a second dose if:

•Your symptoms do not go away completely.

•Your symptoms go away, but then start to come back.

•You used an autoinjector that did not work correctly the first time.

Call for an ambulance (in the US and Canada, call 9-1-1):

●After you use epinephrine – The medicine does not last very long in the body. Symptoms can sometimes come back as the medicine wears off. In the hospital, doctors can watch you and give you more medicine if needed.

●If you think someone is having anaphylaxis, and you do not have epinephrine

Your doctor might also recommend an antihistamine, such as cetirizine (sample brand name: Zyrtec). You can get these without a prescription. They can help relieve mild food allergy symptoms like itching and hives. They do not treat anaphylaxis.

How can I prevent an allergic reaction? — 

The best way is to completely avoid eating the seafood you are allergic to. Even a tiny bite that contains the food can cause a big reaction.

●To know whether a food contains seafood, read its ingredient label. Some countries (including the US) have laws that make companies clearly list whether a food has certain common "allergens" in it. These include fish and crustaceans, but not mollusks.

●Some foods have warning labels for food allergies, such as "May contain fish" or "May contain crustacean shellfish." These might have been made on machines or in factories that are also used for other foods that contain fish or crustaceans. Talk to your doctor about whether you should avoid these foods.

●Many people with an allergy to 1 kind of fish are also allergic to other kinds of fish. The same is true for people with a shellfish allergy. Some people need to avoid all types of seafood. Talk to your doctor about which kinds of seafood you should avoid.

●If you eat at a restaurant, tell your server about your allergy.

What else should I know if I have a seafood allergy? — 

People with a seafood allergy:

●Can have an allergic reaction if they share saliva with (kiss) someone who ate the seafood and did not brush their teeth after

●Can get hives on their skin if they touch the seafood

●Could have an allergic reaction by breathing in tiny droplets of seafood – This can happen when cooking seafood or when in a seafood market.

●Can wear a medical alert bracelet or necklace to tell others about their seafood allergy – If you cannot wear a bracelet or necklace, you can carry a document called an "allergy passport" or "allergy card."

Your doctor or nurse might have you work with a dietitian (food/nutrition expert). They can help you learn how to:

●Avoid the food you are allergic to

●Use other foods in place of the food you are allergic to

●Make sure you get the nutrients you need

Sometimes, people with a seafood allergy are told by a doctor or nurse they need to avoid contrast dye. This is a liquid that makes the results of imaging tests clearer. Some doctors and nurses were taught that people allergic to seafood are also allergic to contrast. But experts have found no connection between these things. It is safe for people with a seafood allergy to get contrast.

What if my child has a seafood allergy? — 

Tell their caregivers, schools, and camps. You should:

●Tell them which foods your child can and cannot eat.

●Make a plan so they know how to treat an allergic reaction.

●Make sure they know where your child's epinephrine is, and how and when to use it.

●Make sure they know how to reach you or your child's doctor in case of an emergency.

Will my child outgrow their seafood allergy? — 

Most children do not outgrow seafood allergy. Your child's doctor will monitor their allergy over time to see whether they outgrow it.

Where can I learn more? — 

You can get more information about food allergies from Food Allergy Research & Education ("FARE") at www.foodallergy.org.

More on this topic

Patient education: Food allergy (The Basics)
Patient education: Hives (The Basics)
Patient education: Angioedema (The Basics)
Patient education: Anaphylaxis (The Basics)
Patient education: How to give epinephrine (The Basics)
Patient education: Allergy skin testing (The Basics)

Patient education: Food allergy symptoms and diagnosis (Beyond the Basics)
Patient education: Food allergen avoidance (Beyond the Basics)
Patient education: Hives (urticaria) (Beyond the Basics)
Patient education: Anaphylaxis symptoms and diagnosis (Beyond the Basics)
Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)
Patient education: Using an epinephrine autoinjector (Beyond the Basics)