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Understanding Shellfish Allergy: Symptoms, Causes, and Management

Written by Andrew Le, MD

UpdatedMay 29, 2024

Food allergy is a growing concern worldwide, affecting individuals of all ages. While many food allergies emerge during childhood, a unique category of allergies tends to develop in adulthood - shellfish allergies.

Shellfish allergies, affecting 2.3% of the general population or around 6.6 million Americans, pose challenges due to the diversity of shellfish and potential cross-reactivity.

In this article, you will learn the details of shellfish allergies, exploring their causes, symptoms, diagnosis, treatment, and prevention strategies.

🔑 Key Takeaways

  • Shellfish allergies are prevalent among adults, affecting over 6.5 million Americans, making it a leading adult-onset food allergy.
  • Pediatric cases of shellfish allergy are concerning, with approximately 1.3% affected; early diagnosis is crucial, as symptoms can manifest in children younger than previously thought.
  • Two main shellfish categories include crustaceans (shrimp, crab) and mollusks (clams, mussels); cross-reactivity is common within each category.
  • Symptoms range from mild (tingling, nausea) to severe (anaphylaxis), emphasizing the importance of awareness and preparedness.
  • Diagnosing shellfish allergies involves skin prick and blood tests conducted by qualified allergists to ensure accurate results.
  • Shellfish allergies are unpredictable, with sensitization increasing the severity of reactions; vigilance and caution are essential.

The Prevalence of Shellfish Allergies

Shellfish allergies are a notable subset of food allergies and are particularly common among adults.

According to Food Allergy Research & Education (FARE), over 6.5 million American adults have allergies to shellfish, making it one of the most prevalent adult-onset food allergies. These allergies can manifest at any point in an individual's life, even if they have previously consumed shellfish without any issues.

Another study showed that the prevalence of seashell allergy in the pediatric population of the US is approximately 1.3%. This is a significant concern, as seashell allergy affects children younger than previously thought, with an average diagnosis age of 16.8 years for crustacean allergy and 19.4 years for mollusk allergy.

Proximity to the coast may influence seashell allergy risk, and seashell allergy prevalence has been increasing since the early 2000s. Many children with seashell allergies do not carry epinephrine auto-injectors, highlighting the need for more outstanding education and awareness.

Types of Shellfish and Allergies

Shellfish are broadly categorized into two groups: crustaceans and mollusks. Both categories encompass various species, each with unique characteristics and allergenic potential. Let’s explore more of these in detail:

1. Crustaceans

Crustaceans are marine arthropods known for their hard exoskeletons. Individuals with shellfish allergies may react to various crustaceans, including:

  • Shrimp
  • Crab
  • Prawn
  • Crayfish
  • Lobster

Cross-reactivity is a common feature of shellfish allergies. If you're allergic to one type of crustacean, you're at a higher risk of being allergic to others within the same category.

2. Mollusks

Mollusks, on the other hand, are soft-bodied marine creatures. Mollusks known to trigger allergies include:

  • Clams
  • Mussels
  • Oysters
  • Squid
  • Cuttlefish
  • Octopus
  • Snails
  • Scallops

Like crustaceans, cross-reactivity among mollusks is also prevalent. Medical professionals often advise individuals with shellfish allergies to avoid all varieties to minimize the risk of allergic reactions.

Shellfish Allergy Symptoms

Shellfish allergies primarily result from the immune system's response to a protein called tropomyosin in shellfish muscles. Shellfish allergy can cause a range of symptoms, from mild to life-threatening, as the immune system reacts to ingested shellfish by releasing histamines and other chemicals.

Here’s the breakdown:

Mild Symptoms

Symptoms of a shellfish allergy often manifest within minutes of consumption and may include:

Severe Symptoms (Anaphylaxis)

In severe cases, a shellfish allergy can lead to a life-threatening allergic reaction known as anaphylaxis. Anaphylaxis requires immediate medical attention and may include symptoms such as:

  • Swollen throat (or lump in the throat) causing breathing difficulty
  • Rapid pulse
  • Extreme dizziness or loss of consciousness
  • Severe drop in blood pressure (shock)

Given the potential for severe reactions, individuals with shellfish allergies must be prepared and informed about the appropriate action in an emergency.

💡 Did You Know?

An allergy attack can have varying durations, mild from a brief sneezing while cleaning a dusty room or severe from ingesting foods like peanuts.

Diagnosing Shellfish Allergies

If you suspect a shellfish allergy, you must undergo proper testing for an accurate diagnosis. Two primary diagnostic methods are commonly employed:

1. Skin Prick Test

In a skin prick test, a tiny amount of shellfish allergen is placed on your skin, typically on your forearm or back. Then, a small needle is used to prick the skin through the drop of allergen. If you are allergic, you will develop a small raised bump or hive at the test site.

2. Blood Test

A blood test, often called a specific IgE blood test, measures the IgE antibodies to shellfish in your blood. Elevated IgE levels can indicate an allergy.

It's important to remember that these tests should only be conducted under the guidance of a qualified allergist or immunologist who can interpret the results accurately.

The Unpredictable Nature of Shellfish Allergies

One distinguishing feature of shellfish allergies is their unpredictability. Allergic reactions to shellfish can be highly variable, with symptoms sometimes appearing long after consuming the allergen and without prior warning signs.

This unpredictability can make it challenging for individuals with shellfish allergies to navigate their dietary choices safely.

Moreover, shellfish allergies often display a phenomenon known as "sensitization." This means that with each exposure to the allergen, the severity of the allergic reaction tends to increase.

Individuals with shellfish allergies must recognize that even a mild reaction in the past does not guarantee a mild reaction in the future. Consequently, vigilance and caution are paramount for those with shellfish allergies.

Managing Shellfish Allergies

A cure for shellfish allergy is currently unavailable, making avoidance the primary strategy for managing this condition. If you have a shellfish allergy, avoiding foods like shrimp, lobster, crab, and other crustaceans is essential.

It's worth noting that while finned fish are distinct from shellfish, cross-contamination remains a common concern, and individuals with severe shellfish allergies may choose to avoid seafood altogether.

The Role of Epinephrine

Many healthcare providers recommend that individuals with shellfish allergies carry epinephrine auto-injectors (EpiPens) for self-administration in case of accidental ingestion. Using epinephrine promptly is crucial in treating anaphylaxis and can be life-saving.

For mild reactions like a rash or itchiness, doctors may suggest an antihistamine such as Benadryl.

When to Seek Medical Attention

Deaths from anaphylactic reactions to shellfish are rare but more common than other food allergies. Physicians generally advise individuals with a shellfish allergy and asthma to keep an epinephrine pen on hand as a precaution.

Trying an antihistamine is a reasonable initial step if a mild reaction occurs, such as a rash or itchy skin. However, immediate medical attention or a visit to the emergency room is imperative if symptoms persist or worsen.

✅ Health Tip

To address an allergy attack, consider using over-the-counter antihistamines to alleviate reactions, decongestants, and eye drops for symptom relief. Explore appropriate care and treatment options for allergy attacks in this article.

Cross-Contamination and Dining Out

Dining out with a shellfish allergy requires a heightened level of vigilance. Cross-contamination is a significant concern, as restaurants often use shared utensils and cooking surfaces. To reduce the risk of exposure, consider the following precautions:

  • Inform your server about your shellfish allergy.
  • Ask about the ingredients used in each dish.
  • Request that your meal be prepared separately to avoid cross-contamination.
  • Avoid buffet-style restaurants where there is a higher risk of cross-contact.

Debunking the Iodine Myth

There has been ongoing confusion surrounding the relationship between shellfish allergies and iodine. Some individuals mistakenly believe that iodine can trigger an allergic reaction in people with shellfish allergies. Iodine is commonly used in medications and as a contrast agent in medical imaging procedures.

This misconception was notably highlighted in a Florida court case where a man with a known shellfish allergy experienced a severe allergic reaction after receiving contrast iodine during treatment for acute coronary syndrome. The man's family received a substantial settlement, alleging that contrast iodine had caused his death.

However, a study published in the Journal of Emergency Medicine has conclusively debunked the notion that iodine is an allergen. The researchers stated, "Allergies to shellfish, in particular, do not increase the risk of a reaction to intravenous contrast any more than other allergies."

Final Words

Shellfish allergies are a significant health concern that affects millions of people worldwide. While there is no cure for shellfish allergies, individuals can manage the condition effectively by avoiding shellfish, carrying epinephrine for emergencies, and staying informed about potential sources of cross-contamination.

Additionally, it is essential to debunk myths about iodine and its connection to shellfish allergies to ensure accurate information is available to those at risk.

By spreading awareness about shellfish allergies and promoting proper diagnosis and management, we can contribute to a safer dining experience and a better quality of life for individuals with these allergies.

FAQs on Seashell Allergy

How long do shellfish allergy symptoms last?

If you're experiencing shellfish allergy symptoms, the duration can vary. Generally, mild symptoms like itching or hives may last briefly, while more severe reactions could persist for several days. However, seeking medical attention to evaluate your case precisely is crucial.

How to treat shellfish allergy at home?

No cure exists; avoid shellfish like shrimp and crab. Watch for cross-contamination, especially with finned fish.

Can shellfish allergy go away?

Unlikely. Around 46% may outgrow shrimp allergy in 10 years. Maintain a shellfish-free diet and keep epinephrine for emergencies.

What medicine for shellfish allergy?

For mild symptoms, take Benadryl. Deaths from shellfish anaphylaxis are rare but more common than with other allergies.