Mackerel Allergy: A Closer Look at Smoked Fish

Mackerel is a predator. The most common species—Atlantic mackerel—is found primarily in the waters of the North Atlantic. It can also be found in the Black Sea, the Mediterranean Sea, and the Baltic Sea. The biggest fans of mackerel are people in Europe (especially Scandinavia) and Japan [4]. In the Land of the Rising Sun, mackerel (known as saba) is a staple on sushi bar menus [4]. In Poland, we enjoy smoked mackerel. It is eaten as a meal on its own and is also often used as a base for sandwich spreads. However, regardless of how it is prepared, mackerel can be dangerous for people with fish allergies.

The main culprit is a protein called Sco s 1 [5]. It belongs to the parvalbumin family—proteins that are responsible for muscle function in fish and enable them to swim quickly [6]. In people with allergies, the immune system mistakenly identifies this protein as a threat and produces IgE antibodies. This leads to the onset of unpleasant symptoms: ranging from hives and swelling of the lips to abdominal pain, and in rare cases, even anaphylactic shock [3].
The Sco s 1 protein is a tough opponent. It is not destroyed by high temperatures during cooking, smoke from smoking, or the digestive acids in our stomach [6]. That is why mackerel in any form—whether canned or smoked—can trigger severe symptoms in a person with an allergy.

It often happens that an allergy to one type of fish leads to problems after eating another—this is known as a cross-reaction [3,6]. This is because the allergenic proteins (parvalbumins) in different fish species have a very similar structure [3,6]. The immune system of an allergic person easily confuses them.

The main allergen in mackerel is less likely to cause such “mistakes” in the body than the proteins found in cod, salmon, or herring [7]. Nevertheless, if you have a sensitivity to fish and seafood, it’s best to exercise caution with different species. The decision to expand your diet should ideally be made only after undergoing thorough testing.

Sometimes eating mackerel can lead to an unpleasant surprise, even for people who aren’t allergic to fish. The cause of these unpleasant symptoms is scombrotoxin poisoning [8]. The term “scombroid poisoning” derives directly from the Latin name for the mackerel family (Scombridae), because historically, mass poisonings were most frequently reported after meals containing these fish. Over time, however, it was realized that fish alone were not to blame, and that other histamine-rich foods (such as aged cheeses) can trigger the same reactions. For this reason, the World Health Organization (WHO) now recommends moving away from this “fish-related” name in favor of a more accurate term: histamine poisoning (or intoxication) [2].

Mackerel, being a very active fish, has a large amount of so-called dark meat, which naturally contains high concentrations of histidine [9]. If the fish is kept out of the refrigerator for too long, bacteria rapidly convert this compound into histamine.

Histamine is completely resistant to heat treatment. This means that if fresh fish has been stored improperly (even for a short time after being caught) and histamine has formed in it, no subsequent processing will destroy it. Neither high cooking temperatures, nor prolonged smoking, nor the canning process can neutralize histamine [10].

The risk of histamine poisoning is associated with the consumption of various species of fish, but mackerel is particularly “tricky.” In Poland, we most often eat it smoked. The intense smoky aroma and high salt content effectively mask the subtle, “peppery” aftertaste that may indicate the presence of the toxin [11].

After eating improperly stored fish, the body gets a “shot” of histamine. The result? The face turns red, the heart beats faster, and hives and shortness of breath appear [11]. Sound familiar? Yes, these symptoms may suggest an allergy. In this case, however, we’re dealing with food poisoning, not an immune system reaction.

Distinguishing a “false allergy” (poisoning) from a true allergy can be challenging. However, there are a few clues that can point you in the right direction.

• Number of people with symptoms:
  If everyone felt sick after a group dinner, the most likely cause was spoiled fish and the histamine it contained. A true allergy is an individual condition, so usually only one person gets sick, even if everyone ate the same thing [10].
• Amount of fish consumed:
  In the case of an allergy to mackerel protein (parvalbumin), even a trace amount of fish or licking a fork can trigger a severe reaction. In cases of histamine poisoning, symptoms depend on how spoiled the fish is and the size of the portion consumed [12].