What are the other Names of this Condition? (Also known as/Synonyms)

• Allergy to Shellfish

What is Shellfish Allergy? (Definition/Background Information)

• Shellfish Allergy is among the most common form of food (seafood) allergy that manifests as an abnormal immune reaction/response to a wide variety of shellfish, in individuals who consume them
• Shellfish is not a type of fish. They are marine creatures with hard exoskeletons (belonging mostly to the crustacean and mollusk family) that commonly include oysters, prawns, shrimps, mussels, lobsters, and crabs. The category may also include animals such as clams, scallops, crayfish, barnacles, snails, squids (and calamari), cuttlefish, and octopus
• Shellfish may be served cooked, fried, smoked, or even raw, in some exotic cuisines around the world. They may also form part of soups, sauce, flavorings, and salads. Shellfish Allergy is caused by a certain protein, called tropomyosin, present in shellfish
• In many, Shellfish Allergy occur immediately, or after a few hours following exposure (food intake). The condition affects adults more than children. It may also develop anytime during an individual’s life
• Numerous signs and symptoms of the allergic reaction may be noted including hives, swollen face and mouth, breathing difficulties, nausea and vomiting, and indigestion. In some individuals, Shellfish Allergy may lead to an anaphylactic shock, which is a medical emergency
• Such food allergies are generally diagnosed using an antibody blood test, a skin-prick test, and an oral food challenge test. The diagnosis can also help identify shellfish food items that are to be avoided (in future)
• Anti-allergic medications form the first line of treatment for mild Shellfish Allergies. However, in the case of a severe allergic reaction (anaphylaxis), epinephrine or adrenaline injections are recommended
• The prognosis of Shellfish Allergy is generally good with appropriate treatment. In many individuals, the condition may persist lifelong. Awareness of such allergies and avoidance of specific foods that causes the allergy (via allergen-free foods) is the best form of prevention

Who gets Shellfish Allergy? (Age and Sex Distribution)

• Shellfish Allergies can occur in children and adults; however, the condition is more common in adults
• It may develop anytime during an individual’s life. Shellfish Allergy is denoted as the most common food allergy arising in adults
• For some reason, boys are affected more than girls, while women more than men, to this type of seafood allergy
• All racial and ethnic groups are equally vulnerable to the condition; however, coastal countries show more cases of Shellfish Allergy than others

What are the Risk Factors for Shellfish Allergy? (Predisposing Factors)

The risk factors for Shellfish Allergy may include:

• Exposure to shellfish: It may be by consuming (eating) shellfish, touching, smelling, smelling while cooking, inhaling steam while boiling, tasting shellfish preparations, or through contact with shellfish remains
• Any family history of seafood allergy
• Having one form of (food) allergy puts one at risk for other forms
• Adults who are exposed to shellfish regularly, either as food or via physical contact, have a higher risk

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Shellfish Allergy? (Etiology)

An allergic reaction occurs in an individual with Shellfish Allergy, because the immune system recognizes certain proteins in shellfish as being dangerous and harmful to the body. The protein in shellfish said to cause the condition is tropomyosin.

• Intake of shellfish results in the production of antibodies, specifically immunoglobulin E (IgE). The next time the individual is exposed to the protein, the antibodies that are circulating in blood causes an antibody-antigen reaction
• This results in the production of histamine and other chemical messengers, which cause the symptoms seen during an allergic reaction
• Some individuals are allergic to one type of shellfish, while others to many, and some to all. Some develop symptoms a long time after taking the allergic seafood
• The quantity of food that triggers an allergy may not be significantly large. Sometimes, consuming tiny amounts of the allergen is sufficient to trigger Shellfish Allergy
• Exercise-induced anaphylaxis: In some individuals, the hypersensitivity reaction occurs when they exercise after having shellfish (after some time); this may be severe causing anaphylaxis
• Non-food items from shellfish that may cause an allergy include garden fertilizer, pet food, certain cosmetics, nutritional products, etc.

In some cases, a severe allergic reaction termed as anaphylaxis may occur, which is a medical emergency that requires immediate medical attention.

What are the Signs and Symptoms of Shellfish Allergy?

The signs and symptoms of Shellfish Allergy may start to appear within a few minutes, to a couple of hours, after the individual has consumed shellfish food preparations. The symptoms may be common to other types of food allergies. In some, the symptoms are mild, while in others they are severe. In many cases, systemic signs and symptoms may be noted.

The signs and symptoms of Shellfish Allergy may include:

• Itching of skin, nose, eyes, inside the mouth
• Tingling sensation in the mouth
• Swollen face
• Urticaria (hives), skin rashes, or eczema
• Coughing, sneezing
• Shortness of breath (trouble breathing), wheezing, asthma-like symptoms
• Runny or stuffy nose
• Nausea and vomiting
• Diarrhea
• Abdominal pain

The symptoms may increase over time; initially, they may be mild and may go unnoticed. Generally, not all episodes of allergy will be of the same severity. In some individuals, the most severe symptom caused by Shellfish Allergies is anaphylaxis.

• Anaphylaxis (sometimes called an anaphylactic shock) is a life-threatening, whole-body allergic reaction
• During anaphylaxis, tissues in various body parts release histamine and other messenger chemicals, which causes swelling of the throat and other symptoms
• Swelling of the throat is especially dangerous as this can cause shortness of breath. If the swelling is not reduced soon, then there is a possibility that the individual could die from a lack of sufficient oxygen
• It can also result in a bluish skin, weak pulse, and decreased blood pressure (hypotension)

How is Shellfish Allergy Diagnosed?

The diagnosis of Shellfish Allergy may involve the following:

• Physical examination, assessment of symptoms, and medical history evaluation (history of allergies in the family)
• Food diary: Once an allergy is suspected, the healthcare provider may request to maintain a food diary, to note what is being consumed on a regular basis and the corresponding symptoms observed. The healthcare provider can help check which shellfish products are causing allergy, through a process of elimination

The tests that are usually conducted to diagnose Shellfish Allergy include:

• Oral food challenge testing; when the individual is administered the allergens in a controlled manner to check for symptoms that develop
• Radioallergosorbent (RAS) test; to determine the specific allergy-causing substance
• Skin-prick test:
  • For this test, tiny amounts of certain substances are injected right underneath the skin (forearm, upper arm, or back)
  • After 15-20 minutes, if the spot where the chemical was injected swells, or if there is redness noticed, then this indicates that the individual may be allergic to the substance
• Blood test to detect antibodies (IgE antibody test)

Note: Do-it-yourself allergy testing kits that are commercially available are usually not recommended by healthcare providers.

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Shellfish Allergy?

The complication of Shellfish Allergy is associated with the allergic reaction itself and it depends on the severity of the reaction. It may include:

• Anaphylactic shock/reaction that may be life-threatening
• Having one form of allergy can make the individual prone to other allergy types
• In severe reactions, a tracheostomy may have to be performed during an emergency situation 

How is Shellfish Allergy Treated?

The treatment of Shellfish Allergy may be undertaken in the following manner:

• Avoiding consumption of any food containing shellfish, which may be identified through elimination diets supervised by a qualified dietitian
• Anti-allergic medication for mild reactions; antihistamine therapy, that is prescribed by the allergy physician
• Symptomatic treatment; use of decongestants, especially for nose block including steroid sprays
• In the case of anaphylaxis (severe allergic reaction), epinephrine or adrenaline is immediately administered
• Breathing support as necessary, control asthma symptoms and low blood pressure
• Immunotherapy, in case of severe allergies, for long-term tolerance development

Provide psychological support to children with such food allergies.

How can Shellfish Allergy be Prevented?

The best way to prevent Shellfish Allergy is to avoid shellfish that the individual is allergic to. Additionally, the following factors may be considered:

• Check ingredients of food before using; educate oneself on foods that potentially contain shellfish
• Parents must be watchful and read food labels, to ensure they do not inadvertently give their child shellfish-containing foods
• Studies have shown that breastfeeding children for 4-6 months or over, can help build their body immunity and make them less prone to allergies
• Appropriate maternal diet during pregnancy can help build stronger resistance (against allergies) in children
• Washing hands with soap and water, in case of contact with an allergen, especially before eating
• Avoiding contaminating food items during food preparation; use separate food utensils for preparing allergy-free meals, when possible
• Generally, avoid all hotels and restaurants that serve seafood, if you are severely allergic to fish or shellfish
• While eating out, explain your food allergy to hotel/restaurant service staff and ensure that your food is without the substances you are allergic to
• In hotels and restaurants, separating the preparation of potential food allergens (such as wheat, tree nuts, soy, fish) from general food preparation counters may be beneficial to individuals with food allergies. This can help avoid cross-contact (allergens getting transferred from one food type to another)
• Generating public awareness on various food allergies
• It is important to note that cooking to high-flame or cooking to recommended standards will NOT ensure elimination of the allergen

In case the child or adult is susceptible to an anaphylactic shock (high-risk individuals) from Shellfish Allergy, the following should be considered:

• Being watchful of triggers and avoiding them
• Wearing medical alert information bracelets or suitable devices
• Carry auto-injector epinephrine or adrenaline medications such as EpiPen, Anapen, or Twinject. Since the condition may recur, it is advised to carry 2 doses (2 pens)
• Supervise children on how to self-administer the injection, if required
• If child is prone to anaphylactic reaction, then information (preferably written instructions) should be given to day care, school authorities accordingly
• Adults should inform their spouses, colleagues, and friends, about the condition, in case of a future emergency

Presently, in many countries, due to labeling and consumer protection laws, foods have suitable labels that indicate their content.

What is the Prognosis of Shellfish Allergy? (Outcomes/Resolutions)

• The prognosis of Shellfish Allergy depends on the severity of the signs and symptoms, but it is generally good with suitable treatment
• Some individuals have it for the rest of their lives, but are able to cope well with modified diets that exclude shellfish
• In some cases, the allergic reaction may be severe, causing anaphylaxis. This is a medical emergency that can lead to a respiratory failure. It requires an immediate treatment of the condition. In such cases, the prognosis is guarded and it depends on whether immediate medical assistance is provided

Additional and Relevant Useful Information for Shellfish Allergy:

It is important to note that those who are allergic to shellfish, may not be allergic to fish and vice versa. However, it is best to check with the healthcare expert on what type of seafood you are specifically allergic to.