Shellfish Allergy

1 What Is Shellfish Allergy?

Shellfish allergy, as the name indicates, refers to an allergic reaction towards some shellfish like crustaceans and mollusks. The reaction is caused by an exaggerated immune response to crustaceans like shrimp, lobster, prawn, crayfish, and crabs, or mollusks like mussels, clams, squid, cuttlefish, octopus, snails, scallops, and oysters. A shellfish allergy is the body’s response to proteins present in certain marine animals.

Some people may be allergic to both groups, while others may be able to eat some shellfish. Generally, people who are allergic to one type are allergic to the other type as well. Symptoms may be mild, like skin rashes, or severe, such as anaphylactic reactions. This food allergy is more common among adults, but may develop at any age. The reactions can range from mild to severe and can even be life-threatening.

Shellfish allergies often persist for the rest of one’s life. It may even develop in people who have eaten shellfish in the past and did not have a reaction. Strict avoidance of shellfish is the best way to treat this allergy. According to Food Allergy Research and Education, more than 6.5 million American adults suffer from allergies to one or both types. Sometimes, shellfish reactions may occur long after a person has consumed the shellfish.  At that time, the person may not show symptoms. In this way, a shellfish allergy is different from other allergies. With each exposure, the allergy become more severe. A shellfish allergy is one of the most dangerous allergies, as it can send a person to the emergency room. This allergy is different from an allergy to fish, so a person who is allergic to shellfish need not avoid fish. 

2 Symptoms

These allergies are mostly due to the immune system’s response to tropomyosin, which is a protein found in shellfish muscles. To attack tropomyosin, antibodies trigger the release of chemicals such as histamine, which leads to a number of symptoms. These symptoms can be mild or may become life-threatening. Most of the symptoms of a shellfish allergy develop within a few minutes of consuming shellfish or shellfish products. Common symptoms are: 

  • Swelling in the lips, tongue, face, throat, fingers, and hands
  • Itching, hives, or eczema
  • Difficulty breathing, congestion, or wheezing
  • Tingling in the mouth
  • Abdominal pain
  • Vomiting or diarrhea
  • Dizziness or fainting
  • Indigestion
  • Wheezing
  • Repetitive cough
  • Trouble swallowing, or a tight, hoarse throat
  • Weak pulse
  • Pale or blue coloring of the skin

Severe allergic reactions caused by any allergen are called anaphylactic reactions. These reactions are a medical emergency that need treatment with an epinephrine injection. Life-threatening reactions to shellfish include:

  • Blockage or swelling in the throat 
  • Rapid pulse
  • Loss of consciousness, dizziness, or lightheadedness
  • Sudden drop in blood pressure

Feeling a lump in the throat may cause difficulty breathing. These severe reactions need immediate medical attention. 

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3 Causes

The immune system’s overreaction is the cause of all food allergies. With a shellfish allergy, the immune system identifies a certain protein from the shellfish as harmful. This triggers antibody production against the protein. The next time you come into contact with the allergen, the immune system releases histamines and other chemicals, which cause symptoms. With continued exposure, these antibodies activate the production of certain chemicals, called histamines, which lead to the typical symptoms of allergic reaction. 

Shellfish are categorized into two types: crustaceans and mollusks. Lobster, crayfish, shrimp, crab, and prawns belong to the crustacean group. Mollusks include squid, clams, oysters, scallops, and snails. Some people may be allergic to only one type of shellfish; these people can still eat shellfish from the other group. 

Others are allergic to both groups, making it essential for them to avoid both types of shellfish. Foods that contain shellfish ingredients may also cause an allergic reaction. Mostly, it is the crustacean group consisting of shrimp, lobster, and crab that causes the greatest number of allergic reactions. Often, people who have this shellfish allergy are able to tolerate the other group (mollusks). Still, consult an allergist before eating any kind of shellfish in case you experience shellfish allergy symptoms.

4 Making a Diagnosis

Symptoms vary from person to person. During each reaction, the same person may not experience the same symptoms, hence, diagnosis of a shellfish allergy is complicated. Sometimes, people who are allergic to shellfish can develop a reaction simply by breathing in fumes or if their food comes into contact with shellfish. The allergic reaction affects the skin, respiratory tract, gastrointestinal tract, and/or cardiovascular system. If you suspect you have a food allergy, consult an allergist. The allergist will perform certain tests to determine whether an allergy exists and, once the diagnosis is confirmed, the allergist will counsel the patient on how to manage exposure and symptoms. A history of symptoms and a physical examination help diagnose the actual cause of the shellfish allergy. Timing of symptoms reveals the chances of an allergic reaction after eating a particular food. The allergist may ask detailed questions, such as what you ate and how much, how long afterwards the symptoms developed, how long they lasted, and what symptoms you experienced.

A physical examination helps rule out symptoms caused by other diseases. Skin tests and blood tests are usually suggested to confirm the diagnosis.

  • Skin test: In this test, a patch of skin is exposed to small amounts of allergen extract. To allow the allergen to go inside, the test patch is lightly pricked with a probe. Inflammation of the skin in the test region within fifteen minutes is a sign of a shellfish allergy. The skin prick is usually done in the upper arm or back. This test is not painful, but can be uncomfortable. It takes about fifteen to thirty minutes.
  • Blood test: This test is recommended if a skin test cannot be performed for some reason, like drug interactions. A blood test is used to measure the number of specific antibodies against the suspected allergen. Increased levels of antibodies indicate a shellfish allergy. It also gives a measure of one’s sensitivity to the allergen. This test is less sensitive than skin prick tests and the results are available in about one to two weeks.

The results will aid the allergist in diagnosing the cause. Although both diagnostic tools may signal a food allergy, neither is conclusive. A positive test to a specific food does not always indicate the person will react again to the same food. However, a negative test will rule out a food allergy. None of the above tests can determine the severity of the allergy.

The allergist may wish to perform an oral food challenge on the patient. In this, a tiny amount of the suspected allergy-causing food is fed to the patient. Over a period of time, the dose is increased. This should be done under strict supervision, and emergency medication and equipment should be kept on hand while conducting this procedure. 

5 Treatment

Currently, there is no cure. It is best to simply avoid the food once it is identified. Carefully read the ingredients label on food products. Be extra careful when you eat out. Be careful when you walk into the kitchen or other areas where food is being prepared, since vapors may carry small particles of shellfish protein, which can cause dangerous reactions in sensitive individuals.  Patients with a shellfish allergy should make some changes in the food they eat. Special cookbooks, patient support groups, and registered dieticians can help you plan your meals. People with a shellfish allergy wonder whether this condition is permanent. There is no answer to this; some allergies to milk or eggs may disappear, whereas others to peanuts and shellfish typically last. Mild symptoms of a shellfish allergy like hives and itching can be treated with antihistamines.

The first line of treatment for anaphylaxis is epinephrine. In anaphylaxis, after exposure to the allergen, symptoms can appear within seconds or minutes and become worse, even deadly. Severe, life-threatening symptoms are treated with an emergency shot of epinephrine.

Injectable epinephrine is now available for convenience and can be carried around to avoid emergency situations. Doctors always recommend people with shellfish allergies to carry epinephrine for self-administration.

 If you are instructed to use an auto-injector, note the expiration date. Ask your allergist how to use it. If you have a history of severe reactions, take epinephrine as soon as you feel one starting or if you suspect you consumed an allergy-causing food. If severe symptoms appear, epinephrine should be taken immediately. Repeated doses may be needed. Common side effects of epinephrine are anxiety, restlessness, dizziness, and shakiness. Rarely can it cause abnormal heart rate, heart attack, sharp increase in blood pressure, and fluid build-up in the lungs. Strict avoidance of shellfish is the best way to avoid an allergic reaction. This includes avoiding food that contains shellfish ingredients. Some nutritional supplements and lip gloss also may contain shellfish ingredients and are hidden sources of the allergy. 

In order to manage food allergies in children, Food Allergy Research and Education has a list of resources for parents, schools, and students. Because of the dangerous shellfish reactions, these symptoms might develop when a child is not with the parent, hence, parents should make sure their school, day care, or other program has an emergency action plan, which would include instructions on recognizing, managing, and preventing these episodes. 

6 Prevention

Avoiding shellfish and products containing shellfish ingredients is the best way to prevent an allergic reaction. Be vigilant while reading labels on food products, as sea food flavoring and fish stock may contain shellfish ingredients. 

Be careful while eating out and avoid eating in seafood restaurants. Broths and sauces made of shellfish can also trigger a reaction, so be careful at buffets and steam tables. Let people know you are allergic to shellfish and, above all, remember to carry an emergency epinephrine shot at all times.

7 Alternative and Homeopathic Remedies

Urtica urens is the most commonly suggested homeopathic remedy for a shellfish allergy. Apis mellifica, arsenic album, natrum mur, and sulphur are also used to alleviate the allergy symptoms. 

Some home remedies for controlling symptoms of the allergy include:

  • Honey
  • Ginger
  • Green tea
  • Peppermint
  • Chamomile
  • Thyme
  • Lime
  • Oatmeal
  • Apple cider vinegar

8 Lifestyle and Coping

Lifestyle modifications are necessary in order to cope with a shellfish allergy.

One should ensure that people around them know about the allergy and take adequate care.

Special care is needed when eating out.

Always carry an emergency shot to avoid sudden, severe reactions.

9 Risks and Complications

Serious, life-threatening reactions to shellfish, called anaphylaxis, are the complications associated with a shellfish allergy.

Risk of anaphylaxis increases if the person has asthma or any other food allergy.

If allergies of any type are common in the family, the person is at an increased risk of developing a shellfish allergy. People of any age can develop this allergy, but it is common in adults. In adults, it is more common in women, and in children, it is more common in boys. 

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