OVERVIEW

What is seafood allergy?

Seafood allergy refers to a series of adverse reactions that occur after consuming fish (such as marine or freshwater fish) or crustacean aquatic animals (such as shrimp, crab, clams, etc.). Medically, it is classified as an allergic reaction ^[1-2].

In seafood allergies, people's allergic reactions to fish and crustacean aquatic animals are not entirely the same.

Is seafood allergy common?

Yes.

For fish allergies, adults currently have a higher prevalence rate than infants and young children, and it generally remains unchanged for life ^[1]. The incidence rate in infants is 0.1%, while in adults it is 2% ^[3].

For crustacean aquatic animal allergies, the incidence rate in infants is 0.2%, while in adults it is 2% ^[4]. Surveys indicate that in China, the prevalence rates of allergies to sea shrimp, river shrimp, and sea crab are as high as 40.3%, 39.0%, and 37.8%, respectively ^[1].

SYMPTOMS

What are the common symptoms of seafood allergy?

Seafood allergy reactions include skin reactions, gastrointestinal reactions, respiratory reactions, oral allergy syndrome, and systemic allergic symptoms ^[5-13].

Patients with seafood allergy may experience the following symptoms shortly after exposure or ingestion, and in severe cases, may also experience collapse or even life-threatening reactions (the severity of seafood allergy symptoms varies among individuals, but for a specific individual, the reaction to a particular type of seafood is usually consistent):

• The most common clinical symptoms are skin reactions, including redness, erythema, itching, severe allergic dermatitis, hives, and angioedema. Hives and angioedema are the most common acute skin symptoms.

• Gastrointestinal reactions are also relatively common, including nausea, vomiting, abdominal pain, and cramps, with severe cases potentially leading to shock.

• Among respiratory reactions, seafood allergy patients may experience nasal congestion, rhinitis, coughing, and asthma, with severe cases potentially triggering allergic syncope.

• Additionally, seafood allergy may cause oral allergy syndrome, primarily manifesting as hives triggered by direct contact after ingestion, mainly affecting the oropharynx (itching and angioedema of the lips, tongue, jaw, and throat), but these symptoms typically disappear quickly.

CAUSES

What is the cause of seafood allergy?

Currently, it is believed that seafood allergies are caused by various proteins present in seafood ^[8,12,14-16].

Fish (mainly parvalbumin): Cod (parvalbumin Gad c 1), salmon (parvalbumin Sal s 1), bigeye tuna (collagen Col), carp (collagen Col - I), blue marlin (transferrin Tf), etc.

Crustaceans (mainly tropomyosin): Red shrimp (tropomyosin Pen a 1), Indian prawn (tropomyosin Pen i 1), Pacific white shrimp (arginine kinase Lit v 2 and troponin-binding protein Lit v 4, etc.), Chinese lobster (tropomyosin Pan s 1), etc. Mollusks among crustaceans, such as squid (tropomyosin Todp 1 and ovalbumin Gald 2, etc.), oyster (tropomyosin Grag 1), etc.

In addition, cross-reactions may occur between different types of seafood. For example, although the tropomyosins in red shrimp and Indian prawn are different, they may trigger the same allergic symptoms ^[17-19].

In which populations do seafood allergies mainly occur?

Seafood allergies occur in both adults and children.

For crustacean allergies, they are more likely to occur in countries where people enjoy eating crustacean seafood (such as shrimp, squid, etc.) ^{[5, 20-25]}. Studies comparing the prevalence of crustacean-induced allergies in different regions worldwide found that in Asian countries where crustacean seafood is popular, crustacean allergies account for 1.19% in Singaporean children aged 4 and above, about 5% in Singaporean and Filipino patients aged 14–16, and only 1.3% in children aged 2–7 in Hong Kong, China. In Western countries where crustacean seafood is less consumed, crustacean allergies account for 0.7% in American children under 16, 0.1% in Danish youth under 22, and are rare in British children aged 6.

Can seafood allergies be transmitted or inherited?

They are not contagious but may be inherited.

If one parent has a seafood allergy, the probability of their child developing a seafood allergy is 30%–40%. If both parents have seafood allergies, the probability increases to 60%–80% ^[26].

DIAGNOSIS

How to Discover Seafood Allergy by Yourself?

There are generally two methods: initially suspecting seafood allergy if symptoms appear after consumption; if you suspect a seafood allergy, you can go to the hospital for allergen testing.

Symptoms of seafood allergy after consumption:

• The most common reaction is skin-related, such as redness, swelling, etc.

• If redness, swelling, or rashes appear on the skin accompanied by itching, the patient should check whether seafood was consumed in the last three meals. If so, it can be preliminarily judged as a seafood allergy.

Hospital allergen testing:

Methods include skin prick tests, fresh food prick tests, and oral challenge tests.

Which Department Should You Visit for Seafood Allergy?

You should go to the Allergy or Immunology Department.

If the hospital does not have these departments, choose based on symptoms.

For common skin reactions like redness or rashes, visit Dermatology. For allergic asthma, go to the Respiratory Department. For allergic rhinitis, consult the ENT Department. In urgent cases (e.g., nausea, abdominal pain, vomiting), visit the Emergency Department.

How Is Seafood Allergy Diagnosed?

Doctors diagnose seafood allergy through epidemiological surveys, allergen tests, and clinical symptoms. In severe cases, preliminary treatment may be given based on surveys and symptoms.

Epidemiological survey includes questions about recent food intake, reaction timing, quantity consumed, and reaction frequency.

Allergen testing commonly involves skin prick tests, where seafood samples are applied to check for significant reactions like large rashes. Other methods include serum-specific IgE tests (blood tests) and oral challenge tests.

What to Do for Severe Itchy Rashes Due to Seafood Allergy?

If you have calamine lotion at home, apply it to relieve itching, but seek immediate medical attention at Dermatology or the Emergency Department.

Note: Avoid scratching the affected area to prevent skin damage and bacterial infection.

TREATMENT

Can seafood allergies heal on their own?

Mild symptoms may resolve on their own, but severe cases require immediate emergency medical attention.

The severity of allergic reactions to seafood varies depending on individual sensitivities. If mild symptoms like redness or swelling occur after consumption, discontinuing seafood intake may lead to recovery. However, severe reactions necessitate urgent hospital care.

Will eating more seafood help build tolerance to allergies?

No.

For individuals with seafood allergies, the only way to prevent reactions is to avoid seafood entirely.

Studies show that fish and crustaceans contain different allergens. After proper medical diagnosis, some may tolerate certain types of seafood under professional guidance^[5]. For example, those allergic to shrimp may not react to cod or other fish.

What are the treatment methods for seafood allergies?

Main approaches include avoidance therapy, food processing techniques, and immunotherapy^[1].

Avoidance therapy involves eliminating allergenic fish/crustaceans from the diet. Many patients require lifelong avoidance after an allergic episode.

Food processing reduces allergen content through methods like heating, irradiation, high-pressure techniques, or enzymatic hydrolysis^[29-30].

Immunotherapy includes standard SIT, T-cell peptide therapy, and recombinant protein mutation therapy, all aiming to reduce IgE binding and allergic responses.

Can I self-medicate for seafood allergies?

No.

All medications carry potential side effects, and improper use may worsen allergic reactions. Suspected seafood allergies require immediate medical evaluation.

Can seafood allergies be permanently cured?

No.

Seafood allergies (particularly fish allergies) typically persist lifelong. No definitive cure exists, and complete avoidance remains the only prevention method.

DIET & LIFESTYLE

What should people with seafood allergies pay attention to in daily life?

First, they should identify their specific allergens and understand which types of seafood commonly trigger their allergies. For example, those allergic to fish should avoid fish products like salmon and cod but may still consume crustaceans (e.g., shrimp, squid).

Additionally, the following two aspects should be noted in daily life:

• Avoid seafood intake: Prevent allergic reactions by strictly avoiding the types of seafood that trigger allergies.

• Maintain a balanced diet: Compensate for protein intake by consuming other high-quality protein sources like eggs and dairy products.

PREVENTION

How to prevent seafood allergies?

The most direct and effective way to prevent seafood allergies is to avoid eating the types of seafood that trigger your allergies. There are no other methods.