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! Learn more about shellfish allergy symptoms, diagnosis, and treatment in the sections below.
Symptoms of a Shellfish Allergy Reaction
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 Testing and Diagnosis
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.
The gold standard of testing encompasses three ways to clinically determine whether someone has a true shellfish allergy or is suffering from shellfish toxicity or poisoning.