If you have an allergy to fish or shellfish, you shouldn't have an allergy to fish oil. That is, unless your fish oil is contaminated with fish or shellfish.
The Way Fish and Shellfish Cause Allergies
Many people who are allergic to shellfish are also allergic to fish, but not as severely, and the fewer people who are allergic to fish tend also to be allergic, although not as allergic, to shellfish.
The common agent in both kinds of allergies is the amino acid histidine, which is especially abundant in the flesh of fish and shellfish. The human body uses histidine to make histamine, which triggers allergy symptoms.
The flesh of fish and shellfish releases large amounts of histidine when it is held for long times without refrigeration. Fish and shellfish that tossed into the hold of a boat or held without refrigeration on a processing plant floor are far more likely to cause allergies than fish that consumed fresh. But what would this have to do with allergies to fish oil?
Not All Fish Oil Products Are Really 100% Fish Oil
If you are experiencing allergies to fish oil, it's probably because the product is contaminated with "fish juice," which may be euphemistically labeled "marine liquids." Omega-3 enriched fish oil actually relieves allergies, but fish byproducts from poor manufacturing processes can cause them.
There are two ways you can tell whether your fish oil contains byproducts that can cause allergies:
If a 1,000 mg capsule contains less than 360 mg of DHA + EPA, then the rest of the contents of the capsule are likely to be fish byproducts that can cause allergies.
If the label on the side of the package lists "marine liquids" as an ingredient, especially as a first-named ingredient, then the product is more likely to cause allergies.
If your fish oil product contains more than a total of 360 mg of DHA + EPA in each 1,000-mg capsule, then there simply is not enough room to contain the impurities that can cause allergies.
One Other Way to Avoid Allergies to Fish Oil
There is one other way to avoid allergies to fish oil that will also help you avoid allergies fish and shellfish. That is to make sure your fish oil product is free of preservatives.
The preservatives BHA and BHT interact with some of the same site receptors that are activated by proteins in decaying fish and shellfish. Sometimes there might not be enough BHA and BHT preservatives to cause an allergic reaction, and there might not be enough marine liquids to cause an allergic reaction, but the combination of all three ingredients will trigger sneezing, wheezing, itching, hives, or shortness of breath.
The best way to make sure you don't suffer an allergy to fish oil is to buy a product that is all-natural fish oil, without the byproducts, and without preservatives.