In the United States, about 1 percent of people live with a fish allergy (or finned fish allergy), most commonly reacting to salmon, cod, tuna, and catfish. Fish is one of the top nine food allergens in the U.S.

If you or your child has been diagnosed with a fish allergy, here’s what you need to know to stay safe.

How Fish Allergies Work

When you live with a fish allergy, it means that proteins in certain fish trigger an immune system response. This reaction can cause allergy symptoms that can range from mild to life-threatening.

Some people diagnosed with a fish allergy are only allergic to one type of fish. Others need to avoid several types or all fish. About half of children who are allergic to one kind of fish will also react to other types. An allergist or another healthcare provider can help determine which fish you or your child should avoid.

Some people have airborne reactions to fish. Some MyFoodAllergyTeam members say they can’t swim in the sea because of their allergy. One member shared, “I can’t even go into the ocean as my skin breaks out in hives and the area swells and becomes very itchy!”

It’s important to know that a fish allergy is different from a shellfish allergy. Fish and shellfish contain different types of protein. Only about 10 percent of people with a fish allergy are also allergic to shellfish.

Healthcare professionals can tell the difference between a finned fish allergy and a shellfish allergy. Common examples of finned fish include salmon, cod, tuna, tilapia, haddock, and flounder. Shellfish include shrimp, lobster, clams, oysters, mussels, and crab.

Symptoms of a Fish Allergy

Some people who live with a fish allergy are diagnosed when they’re children, while others develop it as adults. In fact, up to 40 percent of people who are allergic to fish didn’t have symptoms until they became adults. This makes fish allergies different from many other types of allergy. Some adults develop a fish allergy when working in the seafood industry from being exposed to a high number of fish proteins, which can trigger an allergy.

People who develop a fish allergy as children may outgrow it as they get older, though researchers don’t know exactly how common this is. There’s not enough research available on whether people who develop a fish allergy as adults might stop having the allergy over time.

How Long Do Fish Allergy Symptoms Last?

Most fish allergy symptoms start between a few minutes and two hours after exposure to fish. Some people have a second round of symptoms that starts between four and six hours after they’re exposed. The symptoms are usually gone within a few hours, but for some people, they can last for days.

Symptoms can range from mild to severe. Mild to moderate symptoms might look like:

• Stomach problems, ranging from nausea and cramping to vomiting and diarrhea
• Headaches
• Nasal issues, like sneezing, a stuffy nose, or a runny nose
• Hives
• Asthma attacks
• Mild tightness in the throat
• Face swelling
• An itching or tingling feeling in your mouth

Sometimes, a fish allergy can trigger a life-threatening condition called anaphylaxis. If this happens, you’ll suddenly have problems swallowing or breathing. Symptoms can include:

• Significant swelling of the airway or tongue
• A suddenly hoarse voice
• Wheezing or loud, noisy breathing
• A sudden cough that won’t go away
• Feeling faint or dizzy
• Confusion
• Pale, clammy skin
• Loss of consciousness

If this happens, you need to administer epinephrine right away and seek emergency medical care.

Diagnosing a Fish Allergy

There are several ways doctors can do allergy testing for fish. Your healthcare provider may use one or more of the following tests before making a diagnosis:

• Skin-prick test — Your doctor will place a small drop of fluid containing fish proteins on your back or your forearm, then prick the area with a sterile needle to allow the proteins to enter your body. If you develop a discolored, raised spot within 15 to 30 minutes, it’s a sign you’re allergic to fish.
• Blood test — Lab technicians will test your blood by exposing it to fish proteins and measuring how your immune system responds.
• Food challenge test — In a medical setting, you’ll eat a small amount of fish or a food that contains fish proteins. If you have a severe reaction, the healthcare team can treat it right away.

Treating a Fish Allergy

The best way to manage a fish allergy is to avoid fish. If you’re allergic to one kind of fish, most doctors will tell you to avoid all finned fish to be safe. If you want to find out whether you can safely eat certain types of fish, you’ll need to get tested for multiple varieties. Do not try eating fish on your own before reviewing test results with your allergist and dietitian.

If your allergist is concerned about you having an anaphylactic reaction, they’ll likely prescribe an epinephrine auto-injector, such as EpiPen or Auvi-Q. A nasal form of epinephrine is also available. If you ever need to use epinephrine, call for an ambulance right away and let the dispatcher know you’ve used epinephrine. Depending on your symptoms, your doctor may also recommend antihistamines if you’ve been exposed to fish.

Checking Labels With a Fish Allergy

If you have a fish allergy, avoid all finned fish or the specific types of fish you know cause a reaction. There are more than 20,000 species of fish, so we can’t list them all here.

You should also avoid products that may contain fish, including:

• Fish sticks
• Fish oil
• Fish flavoring
• Fish gelatin

Fish ingredients can appear in foods and products you may not expect. Work with a registered dietitian and always check labels on the following products to make sure they don’t contain fish or a fish product:

• Imitation crab or other imitation fish or shellfish
• Worcestershire sauce
• Barbecue sauce
• Caesar salad and Caesar salad dressing
• Foods from African and Asian countries
• Kimchi
• Bouillabaisse
• Caponata

Even if you can safely eat some types of fish, you should be cautious when ordering fish at a restaurant. Sometimes, restaurants may substitute a less expensive fish for a pricier one without clearly listing the change on the menu.

You’ll also want to be mindful of cross-contamination. When you eat out, clearly tell restaurant staff that you cannot eat food that has come into contact with fish or a certain type of fish. This can also help you reduce the risk of an allergic reaction.

Join the Conversation

On MyFoodAllergyTeam, people share their experiences with food allergies, get advice, and find support from others who understand.

What symptoms do you experience when you have an allergic response to fish? Let others know in the comments below.