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Causes and Symptoms of A Shellfish Allergy

Updated on June 24, 2013

Food allergies are the result of a fault in the body’s immune system that incorrectly identifies certain foods as invaders to the body. The noticeable symptoms of a food allergy are the results of the immune system trying to rid the body of the invading food. A crustacean allergy is a so-called IgE-mediated food allergy with IgE (Immunoglobulin E) being the allergy antibody.

One of the more common food allergies, affecting around 2 per cent of the population is shellfish allergy. There are two groups into which you can categorize shellfish, there are the crustacean such as shrimp, crab and lobster, and then there are the mollusks such as oysters, squid, octopus, scallops and mussels.

Once a shellfish allergy has been diagnosed the best way to deal with it is complete avoidance, however many people who are allergic to shellfish in the crustacean group may be able to tolerate mollusks and vice versa.

Symptoms of A Shellfish Allergy

The severity of reactions to a shellfish allergy can range widely from the mild to extremely severe. The symptoms of shellfish allergies can become apparent within minutes of consuming it, but it can also take a few hours before any reaction becomes apparent. Here are some of the symptoms to look out for.

  • Hives, itching or eczema.
  • Swelling that affects the lips, face, tongue and throat. The swelling can become severe enough to become life threatening.
  • Difficulty in breathing
  • Wheezing or shortness of breath.
  • Nausea or vomiting
  • Diarrhea
  • Abdominal pains.
  • Dizziness
  • Fainting

It is rare that an allergic reaction to shellfish can result in life-threatening anaphylaxis, but it is a symptom that is possible. Anaphylaxis results in breathing difficulties and should be treated as an emergency, getting the patient to the hospital emergency room as soon as possible.

What Is It About Shellfish That Causes An Allergic Reaction

As with other food allergies, the auto-immune system in your body malfunctions and identifies the shellfish protein as harmful to the body. Antibodies are triggered in order to neutralize the protein and histamine in the body are released which are a factor in the allergic reaction symptoms we experience.

People who are allergic to shellfish must also be on guard for products that contain the shellfish proteins to which their bodies react. Some dietary supplements contain shells from crustaceans and although it is indicated by studies that it is unlikely that the allergies will be triggered by the crustacean shells, those who are concerned should avoid taking glucosamine.

Another supplement that potentially contains extracts from shellfish is Omega-3 supplements. These are often made from seafood, most often fish, but it is recommended that you check the label for the ingredients before taking them.

Molluscs - Oyster Allergy Symptoms

An allergy to oysters, as opposed to other kinds of shellfish such as crustaceans, is not as common. The oyster allergy symptoms are very similar to other food allergies with the symptoms usually mild such as oral allergy syndrome. This means conditions ranging from an itching of the lips, throat and larynx to swelling of the lips, tongue, throat and palate. It can become more dangerous with a more commonly reported symptom being urticaria, or hives. However anaphylactic shock can occur after consumption of oysters.

Oysters are bivalve molluscs and so if a person is allergic to other bivalves such as clams, mussels and scallops then there is a good chance that they should avoid other molluscs too. This goes for snails, limpets, cuttlefish, octopus and squid too.

The allergic symptoms after eating oysters usually begin to occur within 90 minutes after eating them, although it’s not unusual that the symptoms present themselves later.

When talking about an oyster allergy we are usually talking about the ingestion of oysters, however symptoms have also been reported after handling them or even after inhaling the steam while cooking.

Spaghetti Made With Squid Ink
Spaghetti Made With Squid Ink

Hidden Shellfish

Sometimes the use of a crustacean in a dish may not be immediately obvious yet the effects will be just as severe. Take squid ink as an example. Squid ink may be used as a food dye, as with its use to color pasta. Similarly the use of cuttlefish ink has the potential to cause the same reaction, being part of the mollusc family.

If is very possible that any dish that has been created with a fish stock base can contain traces of shellfish of some kind or another. Whether the allergy is to shellfish specifically or to molluscs, there is the risk of causing a reaction.

For many people the wisest course of action is to avoid seafood restaurants or dishes that have been prepared by someone who is unaware of your allergy.

Protecting Against Shellfish

There is now a requirement in the US under the Food Allergen Labeling and Consumer Protection Act (FALCPA) that all packaged foods containing shellfish must list the specific shellfish on the label.

Remember that ingredients can change over time and just because a certain type of shellfish wasn’t used by a brand in the past doesn’t mean that it will continue to be absent. Check the label every time you shop.

List of Shellfish To Avoid

  • Barnacle
  • Crab
  • Crawfish
  • Krill
  • Lobster
  • Prawns
  • Scampi
  • Shrimp

According to the FALCPA mollusks are not considered to be major allergens and so will not be specifically noted on product labels. Therefore it is important to be aware of the following mollusks:

  • Abalone
  • Clams
  • Cockle
  • Cuttlefish
  • Limpet
  • Mussels
  • Octopus
  • Oysters
  • Periwinkle
  • Sea cucumber
  • Sea urchin
  • Scallops
  • Snails
  • Squid (calamari)
  • Whelk

Who Might Be Susceptible To A Shellfish Allergy?

There has been some research that indicates that if your parents or someone in your family suffers from shellfish allergy, the chances are high that you may be as well. To avoid inadvertently eating shellfish and suffering either a mild or severe allergic reaction, it is advisable to go to the doctor to get tested.

It appears that women are more likely to have a shellfish allergy than men which could indicate a difference in the immune systems between the sexes. This is merely speculation with no definitive research having been performed yet.

The Likelihood Of Cross-Reactions

There are figures available that suggest that someone who is allergic to one kind of crustacean will have a 75% chance of being allergic to another. This is known as cross-reactivity and the cross-reaction is also valid between crustacean and mollusc allergies too.

Interestingly the cross-reactivity molecules responsible for allergies in crustaceans are also responsible for dust-mite and cockroach allergies.

A Shellfish Allergy Test

The most effective way to find out the extent of your shellfish allergy is to have your doctor perform either a skin test or a blood test. With a skin test your skin is pricked and is exposed to small amounts of the protein found in shellfish and the reaction is assessed in whether a small bump (known as a hive) appears in the skin. A blood test is also referred to as an allergen specific IgE antibody test by measuring the antibodies in the bloodstream as a response to shellfish proteins. It is a test of your body’s immune system and the blood sample is sent to a medical laboratory for testing.

Shellfish Allergy May Be Even More Widespread

There are a number of factors surrounding shellfish allergies that suggest that it could be more widespread than the number indicate. The nature of the various types of shellfish and some folk’s aversion to it could mean that there are people who are allergic to it but are too repulsed by the thought of eating an oyster to find out. The look and smell of shellfish causes many to keep their distance and, who knows, perhaps that is protecting them from coming in contact with an allergen.

Another factor that could be skewing the figures is that the majority of shellfish is quite expensive and so a fair chunk of the community simply can’t afford to buy it.

If you experience any strange feeling after eating any kind of shellfish it is highly advisable that you consult a doctor and get yourself tested for shellfish allergy.


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    • profile image


      7 years ago

      When I was young, I used to eat shrimp. When I was in my 20's, my tongue swelled up from a small bite of shrimp. I had to be rushed to the hospital after eating an oriental cracker that had shrimp oil in it. I ended up in the ER, because I had a sandwich that was next to a shrimp sandwich. I am at the point now, I have to be rushed by an ambulance if I just smell the steam of shrimp. A person was eating a hot shrimp appetizer at the next booth and I had used two epinepherine shots and the perimedics gave me more epinepherine and I barely made it to the hospital. I suggest that everyone carries an epi pin, just in case you are exposed to it.

    • profile image


      7 years ago

      I just had an extreme case of Verdigo a couple weeks ago. I thought I was having a stroke. Went to the hospital and they performed all the normal tests. Last night my husband and I shared some cocoanut shrimp at Outback. I've always been able to eat shellfish, but all night long my hands kept itching. When I got up this morning, I was covered in hives. I feel fine. I took an Allegra. Does anyone know if the Verdigo and my sudden reaction to shellfish could be connected?

    • profile image


      7 years ago

      my love to it shirmp carbs octupos and squid.I am really wondering because everytime i ate them i have a severe abdominal pain.all i know is that when u are allergic you will have hives and itchiness but me i have abdominal pain.after reading this i realize that having abdominal is a symptoms of allergic reactions too.tnx!

    • profile image

      adrian heard 

      8 years ago

      can anyone please enlighten me to the relationship between glandular fever and shellfish allergy. in short, if you are unlucky enough to pick up GF an allergy to crustacea can follow. from the people i have talked to some have heard of it and agreed that it does exist. a definitive answer would be great, as this happened to me. unfortunately my GF became worse over the years and i now suffer chronic fatigue, thus changing my life. anyone else with similar symptoms? would love to hear from people whom have been there and somehow broken through! to all those people who enjoy there shellfish, do not take it for granted!! oh how i yearn for the simple yabby sanger!!!!

    • profile image


      8 years ago

      Well another episode of an allergic reaction to the smell of a Chinese seafood dish with shrimp, being allergic to any shellfish. The smell of it makes me have heavy breathing, itchy eyes, and throat headaches.. Any one else suffer like this? Little frightening when I didn't have an inhaler or Benadryl..

    • profile image


      8 years ago

      Good to hear I'm not alone. Seems many people don't believe me when I say I can eat anything but oysters. I get terrible stomach cramps, nausea, and vomiting for hours. I resort to sleeping on the bathroom floor. The first time I thought it was a "standard" food poisoning. It happened a second time, different restaurant, different season. Third time I caught on. It was me, not them. Each reaction got progressively worse. The last time, I had cardiac symptoms -- arrhythmia -- and bleeding in vomit and diarrhea. I love oysters but they sure don't love mr!

    • profile image

      Marc Carillet 

      8 years ago

      Great stuff here. The information and the detail were just perfect. Many thanks for this very useful info you have provided us.

    • profile image


      8 years ago

      I have never had any allergies to food. All of a sudden, the last two times I've eaten calamari, I have gotten sick. Somewhat different reaction each time with tonight being burping, difficulty breathing, dizzy and nausea. The first time it was diarrhea and vomitting. I'm wondering if I could have developed an allergy to it.

    • profile image


      8 years ago

      A few years ago I had an allergic reaction to crab and shrimp. Didn't realize that Calimari was generated with the same family. I was rushed to the hospital lastnight with life threatening symptoms. I just wanted to warn people that because I don't know squid was the same type of reaction then shell fish

    • profile image


      8 years ago

      I am glad that I found this site. I thought I was alone in my oyster allergy and that it may be in my head. I love clams (cooked or raw), mussles and scallops, but I can not eat oysters.

      Every thing I have read stated that if you are allergic to one bivalve, you will be allergic to them all. So I have tried oysters on 5 occassions throughout my 34 years with the same result.

      Thanks Chris for letting me know I am not the only one and it is not in my head.

    • profile image


      8 years ago

      I am and always have been allergic to shrimp, lobster and crab. All of the best shellfish. Oddly, I can have a bite of shrimp and know intstantly whether or not I can finish it and have another or stop and trash the 2nd half. I can never have more than 2 shrimp as tempting as it is. My reaction is swelling of the throat.

      Once I was tricked by the tiny shrimp and had no reaction, so I had pasta with alfredo sauce and tiny shrimp. In the middle of the night I woke because I couldn't breathe. I swear my airway was reduced to a pinhole. I CALMLY drove myself to the 24 hour Safeway and got Benadryl to counter the allergy.

      Another time, my sis-in-law made stuffed mushrooms, DELISH! I had one, and by the time I reached for the second one I knew there was something in it. I asked and she said it was shrimp. I had to run to Target for Benadryl. Since then, I have Benadryl in my purse, car, desk and bike pouch. Safer then Sorry...

    • profile image


      8 years ago

      I thought I was allergic to all shellfish but had heard that you can 'grow out' of it. I have always been fine with Calimari but then had never associated it with being 'shellfish'. I tried this week to ween myself back on to different kinds of shellfish starting with Scallops which were fine. Then I moved onto King Prawns......big mistake! After 4 hours I had severe stomach pains, was hyperventilating, had numbmess in my hands and feet, felt dizzy and suffered vomiting. After reading this hub I feel much more informed, seems as though I fall into the Crustacean allergic category and am OK with Molluscs!

    • profile image


      9 years ago

      I'm 35 years old and one thing I have learned over my adult years is that I have an allergic reaction to oysters with basically the same symtoms as yours Richbis. I learned of this when I lived in the FLorida Panhandle about 30 miles north of Appilachicola. The oysters were abundant and I learned the hard way of my allergy. And Laura, as I'm typing this I'm currently getting over a reaction due to this 'oyster stuffing' that I had at a relatives home at dinner during the holidays. What's bad is that when she had said she mentioned it before I told her about the allergies, then after consuming a good portion she said 'how'd you like the dressing? That was my oyster dressing I told you about. . .' At this point I was in horror because I knew what the next 48-72 hours held for me and it had been as I always remembered. I love oysters but can't have them. I can't even eat fish that has been fried in the same oil as oysters so I won't eat fried fish from anywhere, its simply not worth it.

    • profile image


      9 years ago

      richbis Right at around the age of 30 I had developed a similar reaction to those delicious oysters, scallops, and conch. I can eat Lobster and shrimp so far no problem.

      My symptoms are also a wicked case of cramping, diahrea and vomiting for hours.

      Without being an "expert" I think it has to do with the animals ability to create it's own shell/home. Whereas the shrimp and lobster have hard exoskeleton.

      I just had to re-explain this for the forth time, in 12 years to my MIL and she doesn't believe me. (And no I don't bring the topic up, she does.) I'm afraid to eat her cooking this Christmas for fear that she's going to "test" me. Oyster stuffing? I think I'm sticking to the pecan pie and the mashed potatoes. I might even try the Scotch.

      We have an aquaintance who died at a Japanese restaurant a few years ago from being exposed to scallops on the table. He didn't eat them. He went into Anaphelatic Shock and suffocated right there in the restaurant.

    • profile image


      9 years ago

      Maine Lobster was my favorite food, I liked oysters, snails, food made with squid ink. I can't eat those now. About 25 years ago at about age 30 I developed an allergy to the above. What's weird is that I can eat Non-Maine lobster and all other shell fish without a problem, thank God. My reaction starts about 4 hours after consumption and it's bad; diahrea and vomiting for hours until I get it out of my system. Once I made Maine lobster for someone and didn't wash my hands after cracking and prepairing it, bad idea, same reaction as having eaten it. Has anyone else experienced this same reaction specifically to the same food? I have to wonder what is in common with the above species that the others don't have?

    • D.Virtual.Doctor profile image

      Funom Theophilus Makama 

      9 years ago from Europe

      This is an amazing hub.... The part which stuck into my cerebrum more is this one "he oyster allergy symptoms are very similar to other food allergies with the symptoms usually mild such as oral allergy syndrome. This means conditions ranging from an itching of the lips, throat and larynx to swelling of the lips, tongue, throat and palate. It can become more dangerous with a more commonly reported symptom being urticaria, or hives"

      It is baffling to know that almost anything eatable is beginning to develop some kind of fight back to man by creating allergic reactions for us.... Is there an evolution going on? Nice hub, and I am privileged reading it. Cheers!


    • profile image

      adrian heard horsham vic 

      9 years ago

      was raised on yabbies and other shellfish until i picked up glandular fever. found out the hard way. decided to make myself a yabbie sanger with salt, pepper, vinegar and heaps of margarine of course being standard. within seconds my parents hardly recognised me due to swelling. just made it to the bathroom when my nose started to bleed. my mother was calling an ambulance as i could not breath due to swelling in my neck and tongue. never, ever will i try shellfish again after that. another time i was sitting out back of my fathers house and was being hit hard by the same symptoms although not as bad as first time. couldn't work out why as had not come into contact with shellfish. found out later a slight breeze was blowing the smell my way from a heap of dumped yabbies behind the house in the alleyway. cant even smell them now, shit do i miss a good old feed of yabbies!!!

    • TrueCures profile image


      10 years ago from Idaho

      You can cure shellfish allergies along with all allergies and then eat whatever shellfish you want.

      The cure doesn't cost a thing. I would be happy to explain how. I'm about to teach the world how from the kindness of my heart. Maybe in time, everyone will know how to cure allergies.

      Nice hub. It was linked to my hub on curing allergies.


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