Seafood Allergies – Causes, Signs and symptoms

Seafood Allergies

Also called: Fish Allergies, Shellfish Allergies


A seafood allergy is an adverse allergic reaction to eating seafood (including fish and shellfish) that can potentially result in death. It is the third most common type of food allergy and affects almost 3 percent of all adults in the United States, according to the American Academy of Allergy, Asthma and Immunology (AAAAI).

Common symptoms of a seafood allergy include hives, itching, upset stomach and nasal congestion. The most severe cases of seafood allergies can result in anaphylactic shock, a potentially life-threatening reaction characterized by difficulty breathing and a sudden drop in blood pressure.

The only way to prevent an allergic reaction to seafood is to completely avoid seafood, products that contain seafood and even areas where seafood is bought, sold or cooked. Allergic individuals must be aware at all times because even seemingly unrelated food products (e.g., marinara sauce, hot dogs) can contain seafood proteins capable of triggering an allergic response. Some people can have allergic reactions just by inhaling the fumes of cooking seafood or through skin contact with the seafood.

Though many people with seafood allergies are allergic to several different types of seafood, others find they are sensitized to only one type of seafood allergen. Only a physician can determine which types of seafood are safe for a person with a seafood allergy. Tests that may be used for this purpose include skin testing, blood testing, an oral food challenge or an elimination diet.

Because the protein in fish responds well to temperature, cooking fish thoroughly can reduce the potency of its allergens. This can allow some individuals with only minor seafood allergies to consume properly cooked fish without a reaction. However, a patient with a seafood allergy should never attempt to eat any kind of seafood without first consulting a physician.

A type of food poisoning that results from eating spoiled fish is commonly mistaken for a seafood allergy. As fish spoil, they build up histamines, which are the substances in the human body that cause allergy symptoms. Eating spoiled fish can release these histamines throughout the body, causing allergy symptoms without any sort of allergic reaction actually taking place.

In addition, toxins that are often present in the water where fish are caught may cause a reaction or a straightforward case of food poisoning.

About seafood allergies

Seafood allergies affect roughly 6.6 million Americans, according to the American Academy of Allergy, Asthma and Immunology. Like other food allergies, seafood allergies can be fatal if a person does not practice strict avoidance of all seafood products. Though most food allergies develop in young children and disappear as they grow older, seafood allergies frequently remain throughout adulthood. In fact, many people first develop seafood allergies as adults. Women are typically affected more than men.

The most serious type of allergic reaction to seafood involves a response known as anaphylactic shock. This potentially fatal condition can be triggered by even a very small amount of a seafood protein.

Three types of seafood can trigger allergic reactions:

  • Fish. There are two main categories of fish: “bony fish” (e.g., salmon, cod, tuna) and “cartilaginous fish” (e.g., sharks). All bony fish share the protein parvalbumin, which is known to trigger allergic reactions. For this reason many people with seafood allergies are allergic to many different kinds of fish. It is not known whether cartilaginous fish also have parvalbumin. However, some people with fish allergies will be allergic to fish in both groups. Cod is the most widely reported fish allergy.

  • Crustaceans. A large group that includes crabs, lobsters and shrimp. It is common for individuals allergic to this kind of seafood to react to all forms of crustaceans (and often mollusks as well).

  • Mollusks. A broad group that includes mussels, oysters and clams. Most people who are sensitive to one type of mollusk are sensitive to them all, as well as all types of crustaceans.

An allergic reaction is triggered in sensitive individuals when a seafood protein (often parvalbumin) makes its way into the body. This process, called an allergic cascade, can begin when the patient:

  • Eats seafood proteins
  • Inhales proteins (e.g., from cooking seafood)
  • Absorbs proteins through the skin (e.g., while handling seafood)

The allergic cascade is triggered when the immune system overreacts to a seafood protein, believing it is a dangerous substance. To combat the protein, the immune system releases IgE antibodies into the bloodstream. These antibodies interact with blood cells (mast cells and basophils) to trigger the release of histamines and other chemicals into the blood.

It is the histamines and other chemicals that stimulate allergy symptoms. By causing blood vessels to swell and individual cells to leak fluid, histamines produce allergy symptoms such as itchiness, rash, hives, stomach cramps, nausea and respiratory problems. Individuals who are sensitive to allergic seafood reactions can go into life-threatening anaphylactic shock, which involves breathing problems and lowered blood pressure.

In some cases, a reaction to fish may be caused by a toxin the fish ingested. Such a toxin may cause an allergic reaction, or it may cause food poisoning (which can be mistaken for an allergic reaction). Bacteria or viruses within seafood may also cause allergy-like symptoms – especially in areas with polluted coastal waters.

Raw fish tends to be the most dangerous form of seafood, provoking the strongest reactions in sensitive people. Cooking fish has proven effective at reducing the ability of the proteins found in fish to start an allergic reaction. Thoroughly cooking fish can make it possible for some mildly allergic individuals to consume fish without a reaction. However, only a physician can determine whether an allergic person can safely consume any type of seafood.

Seafood allergies tend to be more common in countries where seafood is a dietary staple and consumed regularly. In the United States, people are consuming more seafood than past generations. As a result, there has been an increase in the incidence of seafood allergies. Also, susceptibility to seafood allergies is believed to be genetic. Individuals with a personal or family history of any type of allergy (e.g., allergic rhinitis, eczema) are more likely to have a seafood allergy.

Potential causes of seafood allergies

It is possible for individuals who are allergic to one type of seafood to be able to eat other types of seafood without an allergic reaction. However, people with allergies to one type of seafood are often sensitive to other types of seafood in the same class. For example, people who are allergic to one type of shellfish (e.g., lobster, crabs) are usually sensitive to most other types of shellfish. In general, people with shellfish allergies can usually eat fish safely, while people with fish allergies can usually consume shellfish. However, people with seafood allergies should consult their physician before trying to eat any type of seafood. Only a physician can safely determine what types of food are safe to eat.

Though cod is the most common type of fish allergy reported, there are many types of seafood allergies (Note: This is not a complete list):

FishAnchovies, bass, bonito, cod, eel, flounder, grouper, haddock, hake, halibut, herring, mackerel, pickerel, pike, plaice, salmon, sardine, shark, snapper, sole, sprat, swordfish, trout, tuna
CrustaceansCrabs, crayfish (freshwater), lobsters, prawn, rock lobster, shrimp
MollusksAbalone, clams, cockle, cuttlefish, escargot (snails), mussels, octopus, oysters, scallops, squid

In general, children are more likely to suffer from allergies to cod and salmon, while allergies to shrimp, crab and lobster are more common in adults. This is most likely due to dietary differences among these age groups.

People with seafood allergies must also be careful to avoid the many types of foods that contain fish or shellfish products. Even a trace amount of seafood protein can trigger an allergic reaction. Some common products that frequently contain seafood components are:

  • Worcestershire sauce. Contains fish (anchovies).

  • Steak sauce. May contain seafood.

  • Caesar salad. Often contains anchovies either on the salad or in the dressing.

  • Caviar. Made of fish eggs.

  • Marinara sauce. Sometimes contains anchovies.

  • Roe. Unfertilized fish eggs.

  • Surimi (a type of imitation crab popular in some Asian restaurants). Contains fish proteins for added flavoring.

  • Hot dogs, bologna and ham. Can contain fish flavoring (surimi).

  • Pizza toppings. Sometimes contains anchovies.

  • Fried rice and spring rolls. May contain shrimp.

  • Caponata (a Sicilian relish). Can contain anchovies.

  • Coffee and wine. Fish skin is used to clarify some of these drinks.

  • Gelatin-based foods (e.g., marshmallows). May contain seafood.

  • Pet fish food. This dried substance is made of brine shrimp and other seafood. It can easily become airborne and, if inhaled, may trigger symptoms in some people with seafood allergies.

  • Pet food. Dog and cat food may contain seafood.

Allergic individuals should also carefully read the labels of medication, cosmetics, creams and ointments, as some of these products contain fish and shellfish.  

Cooking seafood with other types of food often leads to seafood protein contamination of normally safe foods. For instance, restaurants use vats of oil to fry their foods – often using the same vats to fry shrimp, chicken, French fries and more. Grills and spatulas at restaurants can also become contaminated if they are not cleaned properly after cooking seafood.

Some individuals can be sensitive to the airborne fumes produced by cooking fish. These people can also have an allergic reaction triggered by simply walking through a fish market. Individuals who are this sensitive should be very careful about dining in restaurants or unfamiliar places. Sensitive individuals can also receive an allergic reaction from skin contact with fish and should avoid handling seafood.

Related allergies and conditions

There are several conditions related to seafood allergies. Having other types of allergies, particularly hay fever, asthma or eczema, predisposes a person towards food allergies.

Other related conditions include:

  • Histamine fish poisoning. Some types of spoiled fish (e.g., anchovies, mackerel, mahi-mahi, tuna) contain histamines, the chemicals that trigger allergy symptoms in humans. When a person eats spoiled fish, these histamines can cause hives and flushing very similar to an allergic reaction. However, this reaction is actually a type of food poisoning and not a true allergic reaction. Histamine fish poisoning is very common.

  • Anisakis allergy. A reaction to the parasitic worm Anisakis can mimic a seafood allergy. This intestinal parasite is found in fish and other types of seafood and is considered to be a food allergen capable of producing an allergic reaction. However, this parasite is not a true part of the fish and therefore cannot be considered a seafood allergen. A reaction to this worm usually occurs in raw or undercooked fish.

  • House dust mite-crustacean-molluscs syndrome. There are strong similarities in the allergens found in some kinds of shellfish (e.g., shrimps, mussels, oysters) and those found in some commonly inhaled particles found in the home. The house dust mite-crustaceans-molluscs-syndrome is a type of cross-reaction. It usually involves a person becoming sensitized to a household allergen (often dust mites) and then having an allergic reaction to shellfish (sometimes even the first time they are consumed).

  • Occupational seafood allergy. As the consumption and production of seafood rises, there are increasing reports of allergic reactions taking place in occupational settings. Those who work with the processing of crabs, prawns, mussels, fish and fishmeal are often exposed to skin and aerosolized contact with these foods. As a result, more workers are reporting instances of on-the-job allergic reactions.

  • Red Sea coral contact dermatitis. Skin contact with fire coral can cause hives or blisters to develop on the skin (contact dermatitis). Individuals who have a seafood allergy are more likely to be susceptible to this condition.

  • Aquarium allergy. Because dried pet fish food is often made up of the proteins of brine shrimp and other seafood species, it can cause an allergic response in some individuals. The dried food becomes easily aerosolized and can be inhaled, triggering allergic respiratory diseases such as asthma, allergic rhinitis and bronchitis.

  • Benzoate allergy. This is a type of reaction to benzoate preservatives that are used to treat many kinds of shellfish after they are caught. Many people are allergic to this type of additive. Because shellfish are often treated with very high amounts of the additive, reactions in allergic individuals can be severe.

Signs and symptoms of seafood allergies

Seafood allergies can trigger a variety of allergic symptoms, most of which are very similar to those of other types of food allergies. These symptoms usually appear within two hours of eating, inhaling or touching seafood, but in some cases symptoms can be delayed up to 24 hours.

Reactions to a food allergen can range from mild anaphylaxis (generalized allergic reaction involving two or more body systems) to severe and potentially life-threatening anaphylactic shock. There is no way to predict the severity of reaction when a person with food allergies ingests the problem foods. Therefore, even people experiencing mild symptoms should immediately take a shot of epinephrine and seek medical treatment (see Treatment and prevention).

Mild to moderate symptoms of an allergic food reaction may include:

  • Skin problems. Includes itchiness, hives or swelling.

  • Gastrointestinal problems. Includes stomach cramps, diarrhea, nausea, heartburn and gas.

  • Respiratory problems. Includes wheezing, coughing or difficulty breathing.

  • Nasal or sinus problems. Includes runny nose, nasal congestion or sneezing. These symptoms (associated with allergic rhinitis) are more common when the fumes from seafood are inhaled during cooking, rather than when seafood is ingested.

  • Oral problems. Includes tingling in the mouth or swelling of the tongue and throat.

Mild to moderate symptoms may progress rapidly to more severe symptoms. People having any kind of food reaction should seek immediate medical attention to prevent anaphylactic shock. It is also possible for severe symptoms to appear even when mild to moderate symptoms were not present. Symptoms of a more severe reaction include:

  • Shortness of breath
  • Tightening in the chest or throat
  • Choking
  • Loss of consciousness
  • Drop in blood pressure

Diagnosis methods for seafood allergies

The methods used to diagnosis seafood allergies are very similar to those used in other food allergies. Physicians will generally start by asking a patient about medical history and will perform a physical examination to rule out any conditions with similar symptoms.

To better determine what type of food is the allergen, the physician will often have the patient keep a food diary of everything eaten over a period of weeks or months. This will help demonstrate a correlation between a certain type of food and the onset of allergy symptoms.

When a specific type of seafood is already suspected as an allergen trigger, it can be relatively simple to diagnose a seafood allergy. The most basic question a physician will ask is whether an individual has a consistent reaction to a type of seafood each time it is consumed.

To be sure that seafood is the allergen, a physician will often administer one or more of the following tests:

  • Skin test. Involves scratching, pricking or injecting an individual’s skin with various seafood extracts. The tested areas will react with redness or swelling to indicate an allergic response. Skin testing can help to identify or disqualify specific types of seafood allergens. However, it can be too dangerous to use on highly sensitive individuals.
  • RAST (radioallergosorbent test). A blood test for antibodies that correspond to a specific seafood allergy in a sample of the patient’s blood. Though less accurate than skin testing, it can be used on those people who have reactions that are too sensitive for a skin test.
  • Blinded food challenge test. Considered the most effective way of determining the cause of a food allergy because it supplies the most convincing results. Different foods are placed within capsules to hide their identity. The patient consumes the capsules and the physician looks for signs of an allergic reaction. This type of test is time-consuming and difficult. It is often reserved to confirm suspicions that a patient’s symptoms are not caused by a food allergy. This type of test should be performed only in the presence of a physician who can treat anaphylaxis.
  • Elimination diet. Involves removing all seafood from an individual’s diet for several weeks to see if allergic reactions persist. If reactions stop, it can be presumed that a seafood allergy is present. Seafood may then be briefly reintroduced one-by-one to the patient’s diet under a physician’s supervision. The diagnosis of a seafood allergy is confirmed if and when symptoms resume.

Treatment and prevention of seafood allergies

The only form of treatment for seafood allergies is avoidance – the complete removal of seafood from the diet. Failure to properly avoid seafood proteins could result in a fatal anaphylactic reaction. Though some allergic individuals are able to tolerate some types of seafood, only a physician can determine whether any forms can be eaten safely. People with any type of seafood allergy should stay away from all types of seafood and products containing seafood until they have consulted a physician.

To avoid seafood allergens, allergic individuals will need to be very careful that the products they consume do not contain any seafood ingredients. Some products may unexpectedly contain seafood proteins. Allergic individuals must learn to always check ingredient labels and must learn what kinds of substances to avoid (e.g., surimi). For more examples, see Potential causes.

New legislation may make it easier for people to determine if a food item contains a potential allergen. As of January 2006, food manufacturers are required by the Food & Drug Administration (FDA) to clearly list food allergens on their product labels.

Seafood allergens can easily become airborne in cooking fumes. For this reason, allergic individuals who are sensitive to allergens of this nature should be very careful to avoid locations where fish is being cooked – especially restaurants, cookouts or dinners in an unfamiliar place. Restaurants can be particularly dangerous because many use the same utensils, grills, grease and oil vats to cook and fry seafood as they do with other, normally safe foods (e.g., chicken, french fries). Individuals should always inquire at restaurants about food ingredients and cooking preparation techniques.

Some slightly allergic individuals may be able to tolerate some types of fish when they are thoroughly cooked. Research shows that cooking is effective at denaturing the allergy proteins in most fish (making the proteins less likely to cause an allergic reaction). Raw fish, on the other hand, should always be avoided by people with seafood allergies. A seafood allergic person should always consult a physician before attempting to eat any seafood.

Many physicians recommend that infants and young children under the age of 3 avoid seafood completely. This is to avoid sensitizing children to seafood allergens before their immune systems are mature. After 3, seafood can be gradually introduced to the child, starting with canned tuna, which is the least allergenic form of fish.

Breastfeeding mothers should be careful what they consume, as well. Cod proteins, in particular, have been known to pass through breast milk, sensitizing the infant.

Parents of children with seafood allergies must make sure their child’s school, daycare facilities and clubs are all aware of the child’s condition. Most schools welcome working with parents and will gladly help accommodate any special needs in the cafeteria and in the classroom. Parents should also educate their children when they are old enough to understand their allergies.

Allergic individuals should learn what steps to take if they do have an allergic reaction. For those most sensitive, physicians often recommend that an epinephrine shot be carried at all times. Epinephrine should be taken at the first sign of an allergic food reaction. This powerful bronchodilator can quickly counteract the effects of the potentially life-threatening condition known as anaphylactic shock. These individuals should know how to correctly self-administer their medication. For children, parents and other caregivers should also know how and when to properly treat a severe reaction in a child.

Highly sensitive children and adults may want to consider wearing a medical alert bracelet or necklace that can inform healthcare workers of their condition in the event of an emergency.

Symptom relief for seafood allergy reactions

The only effective treatment for a food allergy is the complete removal of food allergens from the diet. The diligent practice of avoidance is a necessity for anyone suffering from a food allergy.

Every single allergic reaction to seafood has the potential to cause anaphylaxis. For this reason, a person should immediately use an injection of epinephrine if they suspect they are having an allergic reaction. Epinephrine is a synthetic form of adrenaline that, when injected, is a powerful bronchodilator, opening breathing tubes and restoring normal respiration quickly. After using epinephrine, an individual should immediately call for medical assistance.

If an allergic reaction to a food has proved to be only minor (based on a physician’s evaluation), there are some alternatives for the relief of the less serious allergy symptoms These medications can help relieve symptoms somewhat, but are by no means a cure for the condition. Only avoidance of problem foods can successfully treat a food allergy.

Though some allergy medications are available over-the-counter, they should be used only under the direction of a physician. Medications that may be recommended include:

  • Antihistamines. Medications that provide relief for more basic allergy reactions such as hives, sneezing, runny nose and gastrointestinal symptoms. Antihistamines directly counteract the effects of histamines, which are chemicals responsible for most seafood allergy symptoms. With mild symptoms, these drugs are usually administered orally. For more severe allergic reactions, a physician may recommend an injected form of the drug.
  • Bronchodilators. Medications that open the airways of the lung, relieving symptoms such as shortness of breath or wheezing. They may be recommended for people whose seafood allergies trigger asthma attacks or asthma-like symptoms. They are usually breathed directly into the lungs using an inhaler.
  • Corticosteroids. Medications that reduce inflammation. These drugs are often taken regularly to prevent an allergic attack or reduce the severity of symptoms.

Questions for your doctor on seafood allergies

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to seafood allergies:

  1. Do my symptoms suggest a seafood allergy?
  2. What tests will you use to determine if I have a seafood allergy?
  3. Is a seafood allergy dangerous to my overall health?
  4. Can I ever eat seafood again?
  5. Can I assume that I am allergic to all fish and seafood?
  6. Are there other foods I am likely to be allergic to?
  7. What types of food should I avoid?
  8. Are there treatments or medications available to treat my seafood allergy?
  9. Should I carry an allergy kit with me at all times?
  10. What should I do if I accidentally consume seafood?
  11. Is it safe for me to prepare seafood for others?
  12. Are my children more likely to develop seafood allergies because I have the condition?
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