What is a Shellfish Allergy?
A shellfish allergy reaction occurs when your body identifies specific proteins that it perceives as threats, and then tries to fight them off. Your immune system creates an antibody called Immunoglobulin E (IgE) that sets off an immune response. This response can result in a number of different allergic symptoms which range in severity. Although reactions like itching and swelling may seem to be small and just a nuisance, when multiple symptoms occur simultaneously that impact at least two bodily systems — or a single severe reaction such as respiratory distress or throat closing occurs — a shellfish allergy can lead to anaphylaxis and be life-threatening.
What Causes a Shellfish Allergy?
Shellfish allergy is typically caused by tropomyosin, a key protein found in the mollusk and crustacean families. Additional allergens in mollusks include amylase, arginine kinase, myosin heavy chain, and haemocyanin. Tropomyosin is also a shared protein in invertebrate shells.
As a result, insects (such as cockroaches) and arachnids (such as dust mites) can trigger a similar allergic reaction. This similarity creates a high correlation between dust mite allergies and shrimp allergies. Even vegetarians could develop a shrimp allergy through inadvertently breathing in dust mites!
Can You Develop a Shellfish Allergy?
Even if you have never had any issue eating shellfish, it is possible to develop a shellfish allergy at some point in your life. While shellfish allergies can impact anyone, it’s more common to have them develop in adults. In fact, it’s estimated that 60% of people who have shellfish allergies have their first allergic experience as an adult.
Are Fish and Shellfish Allergies the Same?
No. Someone who is allergic to shellfish may or may not be allergic to fin fish, and vice versa.
Can a Shellfish Allergy Go Away?
Shellfish allergies, like all food allergies, can change over time. Unfortunately, the majority of people who do develop a shellfish allergy will have it for their lifetime. Treatment options, including oral immunotherapy, do exist to help build up a tolerance to the allergen and reduce the risk of accidental exposure.
Shellfish Allergy Symptoms
Shellfish allergy reactions can range from mild to severe symptoms. The most common symptoms of a shellfish allergy reaction include:
- Hives or rash
- Swelling in the lips, tongue, mouth, throat, or around the eyes
- Nasal congestion
- Wheezing or shortness of breath
- Nausea or vomiting
- Abdominal pain or discomfort
Severe shellfish allergies can result in anaphylaxis, a severe, life-threatening allergic reaction. In anaphylaxis, the immune system overreacts to proteins in shellfish and mollusks. This causes a rush of chemicals to fight off the invading proteins. Signs of anaphylaxis include:
- Pale or bluish tint on the skin
- Throat constriction
- Shortness of breath
- Difficulty breathing
- Confusion and/or dizziness
- Fainting or loss of consciousness
- Weak, rapid pulse
Anaphylaxis is a medical emergency and must be treated with epinephrine immediately. With severe shellfish allergies, anaphylaxis can occur within minutes. Those with a shellfish allergy are advised to carry two epinephrine auto-injectors to ensure rapid treatment in case of accidental ingestion or contact.
Shellfish Allergy Test
Shellfish allergy can be particularly challenging to diagnose. Although the signs of an allergic reaction tend to be more severe than other food allergies, the resulting symptoms can mirror those of other conditions.
For example, histamine toxicity (scombroid poisoning, which is a form of food poisoning) can present in similar ways to shellfish allergy. Some fish contain high levels of histidine, which the body converts to histamine, creating a response that mimics an allergic reaction. Histamine toxicity most commonly occurs in fish that has not been refrigerated properly or in fish that has spoiled. Other forms of shellfish-related food poisoning that may seem like an allergy include paralytic shellfish poisoning, neurotoxic shellfish poisoning, and amnesic shellfish poisoning.
Oral allergy syndrome (OAS) can also mimic shellfish allergy. This type of food allergy is generally considered to be mild, and occurs when the mouth and throat come into contact with raw vegetables or fruits. OAS shares symptoms with shellfish allergy, such as itchiness of the mouth and throat and swelling in the mouth (in rare cases swelling of the throat), which can make it difficult to separate the two.
Complicating things further, some people who are severely allergic to shellfish don’t have to actually ingest it to have a reaction – they may react if they are in close proximity to shellfish being cooked or if their food touched shellfish.
An allergist can help diagnose a shellfish allergy and the gold standard of food allergy testing encompasses three ways to clinically determine whether someone has a true shellfish allergy or is suffering from another ailment.