What chemical causes seafood allergy

In children, the foods that most commonly cause an allergic reaction are:

  1. milk – if a kid has an allergy to cows’ milk, they’re probably allergic to every types of milk, as well as infants’ and follow-on formula
  2. wheat
  3. eggs
  4. soya
  5. peanuts

In adults, the foods that most commonly cause an allergic reaction are:

  1. tree nuts – such as walnuts, brazil nuts, almonds and pistachios
  2. fish
  3. peanuts
  4. shellfish – such as crab, lobster and prawns

However, any type of food can potentially cause an allergy.

What chemical causes seafood allergy

Some people own allergic reactions to:

  1. mustard
  2. pine nuts (a type of seed)
  3. celery or celeriac – this can sometimes cause anaphylactic shock
  4. sesame seeds
  5. gluten – a type of protein found in cereals
  6. fruit and vegetables – these generally only cause symptoms affecting the mouth, lips and throat (oral allergy syndrome)
  7. meat – some people are allergic to just one type of meat, while others are allergic to a range of meats; a common symptom is skin irritation

The rise in food allergy cases

The number of people with food allergies has risen sharply over the past few decades and, although the reason is unclear, other allergic conditions such as atopic dermatitis own also increased.

One theory behind the rise is that a typical child’s diet has changed considerably over the final 30 to 40 years.

Another theory is that children are increasingly growing up in «germ-free» environments.

This means their immune systems may not get sufficient early exposure to the germs needed to develop properly. This is known as the hygiene hypothesis.

Who’s at risk?

Exactly what causes the immune system to error harmless proteins as a threat is unclear but some things are thought to increase your risk of a food allergy.

Family history

If you own a parent, brother or sister with an allergic condition – such as asthma, eczema or a food allergy – you own a slightly higher risk of developing a food allergy. However, you may not develop the same food allergy as your family members.

Other allergic conditions

Children who have atopic dermatitis (eczema) in early life are more likely to develop a food allergy.

The immune system

The immune system protects the body by producing specialised proteins called antibodies.

Antibodies identify potential threats to your body, such as bacteria and viruses. They signal your immune system to release chemicals to kill the threat and prevent the spread of infection.

In the most common type of food allergy, an antibody known as immunoglobulin E (IgE) mistakenly targets a certain protein found in food as a threat. IgE can cause several chemicals to be released, the most significant being histamine.


Histamine causes most of the typical symptoms that happen during an allergic reaction. For example, histamine:

  1. causes little blood vessels to expand and the surrounding skin to become red and swell up
  2. affects nerves in the skin, causing itchiness
  3. increases the quantity of mucus produced in your nose lining, which causes itching and a burning sensation

In most food allergies, the release of histamine is limited to certain parts of the body, such as your mouth, throat or skin.

In anaphylaxis, the immune system goes into overdrive and releases large amounts of histamine and numerous other chemicals into your blood.

This causes the wide range of symptoms associated with anaphylaxis.

Non-IgE-mediated food allergy

There’s another type of food allergy known as a non-IgE-mediated food allergy, caused by diverse cells in the immune system.

This is much harder to diagnose as there’s no test to accurately confirm non-IgE-mediated food allergy.

This type of reaction is largely confined to the skin and digestive system, causing symptoms such as heartburn, indigestion and eczema.

In babies, a non-IgE-mediated food allergy can also cause diarrhoea and reflux, where stomach acid leaks up into the throat.

Food additives

It’s rare for someone to have an allergic reaction to food additives.

However, certain additives may cause a flare-up of symptoms in people with pre-existing conditions.


Sulphur dioxide (E220) and other sulphites (from numbers E221 to E228) are used as preservatives in a wide range of foods, especially soft drinks, sausages, burgers, and dried fruits and vegetables.

Sulphur dioxide is produced naturally when wine and beer are made, and is sometimes added to wine. Anyone who has asthma or allergic rhinitis may react to inhaling sulphur dioxide.

A few people with asthma own had an attack after drinking acidic drinks containing sulphites, but this isn’t thought to be extremely common.

Food labelling rules require pre-packed food sold in the UK, and the relax of the European Union, to show clearly on the label if it contains sulphur dioxide or sulphites at levels above 10mg per kg or per litre.


Benzoic acid (E210) and other benzoates (E211 to E215, E218 and E219) are used as food preservatives to prevent yeasts and moulds growing, most commonly in soft drinks. They happen naturally in fruit and honey.

Benzoates could make the symptoms of asthma and eczema worse in children who already own these conditions.

Sheet final reviewed: 15 April 2019
Next review due: 15 April 2022

To prevent a reaction, it is extremely significant to avoid every fish and fish products.

Always read food labels and enquire questions about ingredients before eating a food that you own not prepared yourself.

Steer clear of seafood restaurants, where there is a high risk of food cross-contact. You should also avoid touching fish and going to fish markets. Being in any area where fish are being cooked can put you at risk, as fish protein could be in the steam.

More than half of people who are allergic to one type of fish are also allergic to other fish.

Your allergist will generally recommend you avoid every fish. If you are allergic to a specific type of fish but desire to eat other fish, talk to your doctor about further allergy testing.

Fish is one of the eight major allergens that must be listed on packaged foods sold in the U.S., as required by federal law. Read more about food labels

There are more than 20,000 species of fish. Although this is not a finish list, allergic reactions own been commonly reported to:

  1. Herring
  2. Tilapia
  3. Flounder
  4. Hake
  5. Grouper
  6. Swordfish
  7. Catfish
  8. Mahi mahi
  9. Anchovies
  10. Haddock
  11. Pike
  12. Salmon
  13. Sole
  14. Trout
  15. Perch
  16. Bass
  17. Halibut
  18. Cod
  19. Pollock
  20. Snapper
  21. Scrod
  22. Tuna

Also avoid these fish products:

  1. Fish gelatin, made from the skin and bones of fish
  2. Fish oil
  3. Fish sticks (some people make the error of thinking these don’t contain genuine fish)

Some Unexpected Sources of Fish

  1. Caesar salad and Caesar dressing
  2. Worcestershire sauce
  3. Barbecue sauce
  4. Caponata, a Sicilian eggplant relish
  5. Bouillabaisse
  6. Imitation or artificial fish or shellfish (e.g., surimi, also known as “sea legs” or “sea sticks”)
  7. Certain cuisines (especially African, Chinese, Indonesian, Thai and Vietnamese)—even if you order a fish-free dish, there is high risk of cross-contact

Allergens are not always present in these food and products, but fish can appear in surprising places.

What chemical causes seafood allergy

Again, read food labels and enquire questions if you’re ever unsure about an item’s ingredients.

US Pharm. 2012;37(5):HS-14-HS-16.

Intravenous radiocontrast, or IV dye, is used for numerous diverse diagnostic procedures to enhance the images in various radiologic studies. Examples of studies include computed tomography (CT) scans, angiograms, and pyelograms. These diagnostic procedures are done on a daily basis in hospital interventional radiology and cardiology departments around the world. In general, they are used to enhance the visibility of blood vessels.1

There are two basic types of contrast media that are used for most radiologic studies: ionic high-osmolality contrast media and nonionic low-osmolality contrast media.

The latter has become the preferred form of IV dye in recent years, given its better safety record, especially for women who are breastfeeding. However, it is far more expensive than high-osmolality contrast media. Allergy reactions to IV dye are common, can range from mild to moderate, and can sometimes be life-threatening.1

It is believed that people who own an allergy to seafood (shellfish) may show an allergy to contrast media as well, due to the presence of iodine in both. We will briefly review the types, applications, and allergy profile of these products in this article.

Dosing and istration

It is reported that the calculation of contrast media dose and injection rate on the basis of lean body weight leads to increased patient-to-patient uniformity of hepatic parenchymal and vascular enhancement.

This is likely related to the greater perfusion of contrast media to solid organs, muscles, and vessels compared with the highly variable but poorly perfused adipose tissue. As an example, the volume and injection rate of contrast material istration based proportionately on a 70-kg man with 25% body fat or a 70-kg lady with 30% body fat is about 45 g iodine IV at 0.9 g/sec.4

The rate or speed of contrast media injections may increase the risk of an adverse reaction.

What chemical causes seafood allergy

Also, the viscosity or thickness of the contrast media can cause resistance to its flow. The viscosity is related to the concentration, the size of the molecules in a specific contrast agent, and the temperature of the contrast agent. Contrast media with higher viscosity values should be injected at a slower rate. Heating the contrast media, generally to body temperature, reduces viscosity. Iodine concentration, viscosity, temperature of the contrast media, catheter inner diameter, catheter length, and the number of catheter holes are every factors that influence contrast media flow.1

Allergy Prevention and Treatment

As mentioned above, the purpose of using these contrast agents is for diagnosis, but love any medical procedure in any radiological study, the correct dose or volume of contrast media needs to be sure prior to a procedure.

The entire volume or dose is dependent upon several factors: iodine concentration of the contrast media; type of injectable contrast media (ionic or nonionic); patient’s body weight, anatomical structures or regions; speed of the injection; and age or disease process that could increase the risk of an adverse reaction. The treatment of an acute reaction to contrast media is no diverse from any other anaphylactic reaction. Treatment may include injectable epinephrine and antihistamines, as well as the use of IV fluids for low blood pressure and shock.7

Contrast media reactions can be prevented by a test dose for the intended contrast or the use of an alternative; the use of nonionic versus ionic media if applicable; and the use of certain medicines prior to the istration of contrast media such as prednisone 50 mg orally taken at 13, 7, and 1 hour prior to procedure, or diphenhydramine (Benadryl) 50 mg orally, IV or intramuscularly, 1 hour prior to receiving radiocontrast media.7

Types of Radiocontrast Media

Both high-osmolar contrast media (ionic) and low-osmolar contrast media (nonionic or organic) agents contain iodine and are istered intravenously.

Most intravascular contrast media are derivatives of tri-iodobenzoic acid. The iodine molecule is an effective x-ray absorber in the energy range where most clinical systems operate. Iodinated contrast media are the most efficient products to enhance the visibility of vascular structures and organs during radiographic procedures. The ionic type creates more charged particles and causes a high osmolality in blood, which may cause a potentially life-threatening contrast media reaction in some individuals with medical conditions.

The nonionic agents generate less dissociation and particles and decrease this risk, but are much more expensive. The nonionic contrast media are much more widely used today. The iodine concentration of contrast media is sure by the number of iodine molecules in milligrams present in a milliliter of a solution (mg/mL).2

Concentration of any contrast media agent determines how radiopaque the agent will be. The higher the iodine concentration, the better the chance that more x-ray photons will be absorbed. Therefore, that specific contrast agent may be more radiopaque than a comparable low-iodine concentrated agent.

The osmolality of a solution is the measurement of the number of molecules and particles in a solution per kilogram of water.

In other words, osmolality can be described as a measurement of the number of molecules that can crowd out or displace water molecules in a kilogram of water. The radiographic significance of the osmolality worth of contrast media is that it is higher than the osmolality worth of blood plasma. Any solution that has an osmolality worth greater than blood plasma is said to be a hyperosmolar solution. Therefore, ionic and nonionic contrast media are hyperosmolar solutions when compared to blood plasma.

Since certain radiographic procedures, such as myelography, cannot use ionic contrast media, the discovery of nonionic contrast media in 1974 (e.g., metrizamide) revolutionized these procedures.2


In most cases, shortly after infusion, iodinated contrast media cause a warming sensation throughout the body.

In certain areas of the body this feeling is more pronounced. Patients receiving contrast media via IV typically experience a boiling feeling around the throat, and this boiling sensation gradually moves below to the pelvic area.

Reactions to IV dye are observed in 5% to 8% of patients who get them. Mild reactions include a feeling of warmth, nausea, and vomiting. Generally, these symptoms happen only for a short period of time and do not require treatment.

What chemical causes seafood allergy

Moderate reactions, including severe vomiting, hives, and swelling, happen in 1% of patients receiving contrast media and frequently require treatment. Severe, life-threatening reactions, including anaphylaxis, happen in 0.1% of people receiving contrast media, with an expected death rate of one person in every 75,000. The most severe reactions, including death, own been reported to happen at similar rates with both types of contrast media.5

Reactions to contrast media are not a true allergy, but rather a pseudoallergy in nature, meaning that there is no allergic antibody present that causes the reaction.

Rather, contrast media act to directly release histamine and other chemicals from mast cells. The iodine concentration has an effect on the severity of an adverse reaction. The higher the iodine concentration, the greater the risk of an adverse reaction.9

Iodinated contrast media are toxic to the kidneys and kidney functions. The serum creatinine of the patient receiving a dose should be monitored before the procedure. In addition, the estimated glomerular filtration rate (eGFR) should be no lower than 30 mL/min in patients receiving iodinated contrast, and discretion should be used in patients with eGFR less than 45 mL/min.

Following injections with additional fluids is highly recommended.1

Numerous studies own shown that although iodine is common in contrast media, iodine is not the cause of allergic reactions.

What chemical causes seafood allergy

Certain proteins in seafood, rather, are the cause of allergy in patients with seafood allergies. It is noted that true allergic effects are by definition immunoglobulin E–related, and studies own shown that contrast media cause no such reaction in vivo. Therefore, contrast media or the iodine is not likely to act as an allergen.5

Contrast Media Applications

Examples of currently used ionic and nonionic contrast media are perflutren-protein type-A microspheres injection (Optison), iohexol injection (Omnipaque), and nonionic iodixanol injection (Visipaque).

Optison is used in patients with suboptimal echocardiograms to opacify the left ventricle and to improve the delineation of the left ventricular endocardial borders.

Omnipaque is used for angiocardiography; aortography including studies of the aortic root, aortic arch, ascending aorta, and abdominal aorta and its branches; contrast enhancement for CT scan of head and body imaging; IV digital subtraction angiography (DSA) of the head, neck, abdominal, renal, and peripheral vessels; peripheral arteriography; and excretory urography.

Nonionic or organically bound iodine contrast media such as Visipaque (270 mgI/mL) are used for DSA.

Visipaque Injection (320 mgI/mL) is used for angiocardiography, peripheral arteriography, visceral arteriography, and cerebral arteriography. Visipaque Injection (270 mgI/mL and 320 mgI/mL) is indicated for CT of the head and body (excretory urography). Visipaque Injection (270 mgI/mL) is also indicated for peripheral venography. Another example of the nonionics is Isovue-300 (iopamidol), which is used to assist diagnosecertain disorders of the heart, brain, blood vessels, and nervous system.1,3

Radiocontrast Media Allergy Diagnosis

Skin testing and RAST (radioallergosorbent test) own not been helpful in the diagnosis of contrast media allergy.

Little “test” doses are also not helpful, with reports of severe, life-threatening reactions occurring even at such amounts. Severe reactions to larger doses of contrast media own been observed after a person tolerated a little dose of IV dye. Therefore, the diagnosis of contrast media allergy is made only after symptoms own occurred. Otherwise, it is only possible to determine that a person is at increased risk of a reaction to contrast media based on the risk factors outlined below.6

Risk Factors

As mentioned above, people who own seafood allergy are not at risk if they need to use contrast media. In addition, people with an allergy to topical iodine cleaners or iodides are also not at increased risk for reactions to contrast media.

Patients who are at higher risk include those with past reactions to contrast media (up to 44%); those with asthma; those who own a history of heart and kidney and thyroid (both hypo- and hyperthyroidism)diseases; those taking beta-blockers or metformin; and females and the elderly (appear to be at higher risk for severe reactions).8,11

Note: Timely follow-up of serum creatinine levels in patients with diabetes who are receiving metformin therapy is highly significant, and monitoring is required by pharmacists. Almost 4% of patients with diabetes mellitus and normal renal function may develop contrast material–associated neuropathy with nonionic contrast media.

Roughly 8% of patients with diabetes receiving metformin, whose baseline serum creatinine levels are under 1.5 mg/dL, develop an increased risk of lactic acidosis requiring metformin therapy to be withheld for at least 48 hours after istration of IV contrast material. The FDA currently recommends metformin monitoring in patients who are undergoing radiologic procedures involving istration of IV contrast media.11


1. American College of Radiology (ACR) Manual on Contrast Media. 2010. Version 7.
2. Meth MJ, Maibach HI. Current understanding of contrast media reactions and implications for clinical management.

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3. Thomson K, Varma D. Safe use of radiographic contrast media. Australian Prescriber. 2010;33:19-22. www.australianprescriber.com/magazine/33/1/19/22/.
4. Ho LM, Rendon C. Nelson RC, DeLong DM.Determining contrast medium dose and rate on basis of lean body weight: does this strategy improve patient-to-patient uniformity of hepatic enhancement during multi–detector row CT?Radiology. 2007;243,431-437.

What chemical causes seafood allergy

5. Boehm I. Seafood allergy and radiocontrast media: are physicians propagating a myth? Am J Med. 2008;121(8):e19.
6. Barrett BJ, Parfrey PS.

What chemical causes seafood allergy

Preventing nephropathy induced by contrast medium. N Engl J Med. 2006;354:379-385.
7. Tramer MR, von Elm E, Loubeyre P, Hauser C. Pharmacological prevention of serious anaphylactic reactions due to iodinated contrast media: systematic review. BMJ. 2006;333:675.
8. Canter LM. Anaphylactoid reactions to radiocontrast media. Allergy Asthma Proc. 2005;26:199-203.

Brockow K. Contrast media hypersensitivity: scope of the problem. Toxicology. 2005;209:189-192.
10. www.medscape.com/viewarticle/489319_5.
11. Keller DM,Iodinated contrast media raises risk for thyroid dysfunction.Arch Intern Med. 2012;172:153-159.

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Anaphylaxis is a severe, sudden, and potentially fatal allergic reaction to a foreign substance or antigen that affects multiple systems of the body.