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Shellfish allergy — tongue vs immune system

Shellfish allergy — tongue vs immune system

What your tongue finds delectable may be seen as a threat by your immune cells, eliciting a spectrum of negative reactions

Shellfish allergy is one of the most common food allergies.

“Crab cream dumplings are my favourite. I’d gorge on it as a kid, but I have had to steer clear from shellfish for the past two years,” says Anna (name changed on request), a 20-year-old from Colorado, who developed shellfish allergy.

It all started in 2020, when Anna was 18 and began working as a server at a seafood restaurant. She decided to try their best-selling shrimps. “In 15 minutes, I blew up in hives, my throat closed and I was gasping for breath,” she says. “I couldn’t make sense of what was happening.”

Anna was rushed to a hospital and given an anti-allergy medicine and steroids and kept on observation for two hours. At the allergist’s, they did arm pricks (skin prick test) of shellfish, garlic and lemon (the seasoning used on the shrimps was garlic and lemon).


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In the presence of an allergy, an allergic reaction is seen on doing a skin prick test. Strangely, Anna showed no reaction at all. Her shellfish allergy was finally diagnosed with a blood test. 

Shellfish and safety

Her job requires her to serve plates of shellfish. She is vigilant that it doesn’t touch her skin.

Every time she eats out, Anna mentions about her allergy to the server. “I also look out possibilities of cross-contamination,” she says.

She recounts accidentally eating a crunch crab sushi roll. “I didn’t realise until I had two or three pieces,” she says. “Fortunately, I didn’t react. Probably the sushi contained imitation crab. Some people allergic to shellfish don’t react to imitation. But I haven’t tested that theory again. I don’t feel like stabbing an expensive epinephrine for an experiment rather than when I really need it.”

She always carries epinephrine, a life-saving a self-injectable automatic adrenaline dispenser, to help her with any life-threatening allergic anaphylaxis reactions.

“Shellfish is the best food, and it is appalling to avoid them and constantly be on high alert, but it is what it is,” she says.

What is a shellfish allergy?

According to Dr Sukesh Rao, professor and head, department of respiratory medicine, Srinivas Institute of Medical Science and Research, Mangaluru, Karnataka, allergy is an abnormal reaction of the body to a typically harmless stimulus.

“If you experience any abnormal or exaggerated bodily reactions after eating shellfish, it is a shellfish allergy,” says Dr Rao.

According to Dr Anil Kumar Gandham, consultant pulmonologist at Care Hospitals, Visakhapatnam, Andhra Pradesh, shellfish allergy is one of the most common food allergies. “Shellfish belongs to two categories: crustaceans (prawns, crabs, lobsters) and molluscs (mussels, oysters, squids),” he says. “While some are allergic to one type of shellfish, some will react to all. Sometimes, the allergy is restricted to one category, either crustaceans or molluscs. Allergy to crustaceans is more common.”


Watch out for cross-contamination

An allergic reaction may not solely be restricted to eating shellfish. “Eating shellfish in direct or concealed form is the commonest trigger, but merely touching shellfish can elicit symptoms like itchy hands and eczema in some,” says Dr Anita Kamath Dudhane, a consultant allergist from Goa.

According to Dr Gandham, an allergic reaction can also be triggered by cross-contamination. “Using common utensils or surfaces for cooking can lead to shellfish getting into other foods, causing benign foods to acquire allergic tendencies,” he says. “In individuals with a severe allergy, passing by an area where shellfish is processed can set off a trigger.”

Sea-food eateries and restaurants specialising in Asian cuisines carry a higher risk of cross-contamination because shellfish is an important part of the menu. The chances of shellfish being present as a hidden ingredient in the form of seasonings and condiments are also high in these restaurants.

“Shellfish in hidden forms include Southeast Asian delicacies that use seafood paste in their curries,” says Dr Dudhane. “Goan dishes like Balcao and Kismoor contain dried prawns.”

Symptoms of shellfish allergy

According to Dr Dudhane, symptoms generally start within minutes to an hour after eating or coming in contact with shellfish. The reactions can range from mild to severe.

“Anaphylaxis is a severe, potentially life-threatening allergic reaction,” says Dr Dudhane. “It can occur within seconds to minutes after exposure to the allergen and worsens quickly. Anaphylaxis causes the release of chemicals that can cause a patient to go into shock.”

Dr Rao says anaphylaxis starts with breathing difficulty, followed by a choking sensation. The person may collapse or become unconscious. Their blood pressure drops, pulse weakens and they may also go into a coma.

Dr Rao lays down the common reactions which are also observed in other food allergies:

  • Skin symptoms
  • Itching
  • Rashes
  • Hives
  • Redness
  • Respiratory symptoms
  • Choking sensation
  • Cough
  • Wheezing
  • Bronchitis
  • Asthma
  • Nasal stuffiness
  • Difficulty swallowing.

Dr Gandham mentions gastrointestinal symptoms like:

  • Diarrhoea
  • Abdominal cramps
  • Vomiting
  • Swelling, dizziness, light-headedness and fainting are also seen.

Diagnosing shellfish allergy

According to Dr Dudhane, case history is a common method of diagnosis. Other methods include food allergy tests, including a skin prick test and radioallergosorbent test, a blood investigation which determines the substance a person is allergic to. 

Treatment of shellfish allergy

“Milder reactions are treated with antihistamines,” says Dr Dudhane. “Long-term management of shellfish allergy [requires] avoiding shellfish in all forms.”

In patients with severe allergic reactions like anaphylaxis, she recommends carrying epinephrine. “An anaphylactic reaction to shellfish is a medical emergency,” she says. “It requires immediate treatment with an adrenaline injection. Sometimes the reaction can recur after 12 hours and so it’s very important to be alert. If not treated immediately, it can be fatal.”

Dr Gandham recommends avoiding seafood restaurants and being vigilant of ingredients by reading food labels and checking with restaurants whenever dining out.

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