What are the side effects of mackerel fish?

December 10, 2025 •

4 min read

While celebrated for its omega-3 fatty acids, mackerel can present several health risks if not properly selected and prepared. The potential side effects of mackerel fish range from heavy metal exposure to foodborne illnesses, making it essential for consumers to be aware of these dangers.

Quick Summary

The consumption of mackerel carries risks including mercury contamination, scombroid poisoning from histamine, allergies, high purine levels for gout, and potential parasite exposure.

Key Points

Mercury Content: King Mackerel and Spanish Mackerel can contain high mercury levels, posing risks, especially to pregnant women and children.
Scombroid Poisoning: Improper refrigeration can cause bacterial growth that produces histamine, leading to allergy-like symptoms like flushing, rash, and headaches.
True Fish Allergies: Mackerel can trigger allergic reactions ranging from mild hives to severe anaphylaxis in sensitive individuals, and cooking does not remove the allergen.
High Purine Content: High purine levels in mackerel can exacerbate gout symptoms by increasing uric acid in the blood.
Parasite Risk: Consuming raw or undercooked mackerel carries a risk of parasitic infections like Anisakiasis, which is preventable by cooking thoroughly.
Canned Mackerel Sodium: Preserved canned mackerel can contain excessive sodium, which is a concern for individuals with high blood pressure.
Safe Consumption: To minimize risks, choose low-mercury species like Atlantic mackerel, ensure proper storage, and limit consumption for certain health conditions.

Mercury Contamination

One of the most significant concerns with consuming mackerel is its potential mercury content. Mercury is a heavy metal that can accumulate in the flesh of fish, and levels vary significantly depending on the species and size.

High-Risk Species

Certain species, particularly larger, longer-living predatory fish, accumulate higher levels of mercury. King Mackerel, for instance, has a high mercury concentration and should be avoided by vulnerable populations like pregnant women, nursing mothers, and young children. Spanish Mackerel can also contain elevated levels, especially in larger specimens.

Low-Risk Species

In contrast, species like Atlantic Mackerel and Pacific Mackerel are known for having low mercury levels, making them a safer choice for more frequent consumption. The FDA provides guidance on which fish are safest to eat.

Scombroid Poisoning (Histamine Toxicity)

Scombroid poisoning is a form of food poisoning caused by consuming fish with high levels of histamine. This happens when fish from the Scombridae family (which includes mackerel, tuna, and mahi-mahi) are not properly refrigerated after being caught. Bacteria on the fish convert the naturally occurring amino acid histidine into histamine. A critical point is that cooking, smoking, or freezing does not destroy the histamine once it has formed.

Symptoms typically appear within minutes to a couple of hours and resemble an allergic reaction. These can include:

Facial flushing or rash
Sweating
Headache and dizziness
Nausea, vomiting, and abdominal cramps
Burning or tingling sensation in the mouth
Hives

While usually mild and resolving within 12 hours, severe cases may require immediate medical attention.

Allergic Reactions

A true fish allergy, distinct from histamine toxicity, is a reaction to proteins within the fish, most commonly parvalbumin. For some individuals, mackerel can trigger an allergic response. The protein is heat-stable, meaning both cooked and raw fish can cause a reaction.

Symptoms of a fish allergy can vary from mild to severe and may include:

Hives or a skin rash
Nausea, stomach cramps, and diarrhea
Stuffy or runny nose
Headaches
Anaphylaxis, a severe and life-threatening reaction that requires immediate medical intervention

Mackerel and Gout

Gout is a form of arthritis caused by high levels of uric acid in the blood. Mackerel is high in purines, which are compounds that the body breaks down into uric acid. For people prone to gout attacks, consuming high-purine foods like mackerel can trigger a flare-up. It is recommended for individuals with gout to limit their intake of mackerel and other high-purine seafood.

Other Risks: Ciguatera and Parasites

Beyond mercury and histamine, other less common but still notable risks exist. Ciguatera poisoning is a risk, particularly with Spanish Mackerel caught in warmer waters. This toxin is produced by marine algae and accumulates up the food chain. Cooking or freezing does not eliminate the toxin.

Additionally, raw or undercooked mackerel can contain parasites, such as the Anisakis simplex nematode. To prevent infection, all mackerel should be cooked to an internal temperature of 145°F (63°C).

Canned Mackerel and Sodium

While convenient, canned mackerel can contain very high levels of sodium, which is added as a preservative. Individuals with high blood pressure or those on a salt-restricted diet should check labels and opt for low-sodium varieties or rinse the fish thoroughly.

Mackerel Species Comparison


Feature	King Mackerel	Atlantic Mackerel
Mercury Level	High	Low
Recommended Intake	Avoid for vulnerable groups; limited consumption for others	Two servings per week for most people
Scombroid Risk	Yes, if mishandled	Yes, if mishandled
Ciguatera Risk	High risk, especially in warm-water areas	Very low risk
Source	Predatory fish in warm waters	Smaller fish in North Atlantic

Conclusion

While mackerel is a nutritional powerhouse rich in omega-3 fatty acids, consumers must be vigilant about its potential side effects. By choosing low-mercury species like Atlantic mackerel, ensuring proper refrigeration to prevent histamine toxicity, and cooking the fish thoroughly, most people can safely enjoy its health benefits. Individuals with pre-existing conditions like gout or a fish allergy must exercise extra caution. For those concerned about mercury levels, the U.S. Food and Drug Administration provides comprehensive guidance on safe fish consumption: https://www.fda.gov/food/consumers/advice-about-eating-fish.

Safe Consumption Guidelines

Choose the right species: Opt for low-mercury varieties like Atlantic or Pacific mackerel over high-mercury King or Spanish mackerel.
Prioritize freshness: Ensure the mackerel is properly refrigerated from the moment it is caught to prevent scombroid poisoning.
Store correctly: For long-term storage, freeze fresh mackerel. If buying canned, check the sodium content and consider rinsing.
Cook thoroughly: Always cook mackerel to an internal temperature of 145°F to eliminate parasites and bacteria.
Moderate intake: Even low-mercury mackerel should be consumed in moderation, ideally within weekly seafood guidelines.
Listen to your body: If you experience any symptoms after eating, stop consumption and consult a medical professional.

Following these steps can help mitigate the side effects and maximize the nutritional benefits of this popular fish.

Frequently Asked Questions

King Mackerel should be avoided due to high mercury content, especially by pregnant women and young children. Spanish Mackerel, particularly large ones, also have elevated levels and should be limited.

Scombroid poisoning is caused by histamine from spoiled mackerel that has been improperly refrigerated. Prevent it by ensuring mackerel is always kept cold, as cooking does not destroy the toxin once it has formed.

No, they are different. A mackerel allergy is a reaction to a specific protein in the fish, while scombroid poisoning is a reaction to histamine produced by bacteria in spoiled fish. An allergy is a true immune response, whereas scombroid poisoning is a form of toxicity.

It is generally not recommended to eat large amounts of mackerel if you have gout, as it is high in purines. Purines can increase uric acid levels and potentially trigger a gout flare-up.

Yes, canned mackerel is safe, but be mindful of its high sodium content. It's best to choose low-sodium options or rinse the fish to reduce excess salt, especially if you have high blood pressure.

The most effective way to avoid parasites like Anisakis is to cook mackerel thoroughly. The FDA recommends cooking fish to an internal temperature of 145°F (63°C).

For low-mercury species like Atlantic mackerel, two to three servings per week are generally considered safe for healthy adults. However, intake should be lower for vulnerable groups like pregnant women and young children, following specific FDA guidelines.