Who Should Avoid Eating Fish? A Guide to Mercury, Allergies, and More

November 14, 2025 •

3 min read

According to the U.S. FDA and EPA, pregnant women, nursing mothers, and young children are advised to avoid high-mercury fish due to developmental risks. This guide explains who should avoid eating fish and why, covering allergies, compromised immunity, and specific health conditions.

Quick Summary

Examines key groups who must restrict or avoid fish consumption, including those at risk from high mercury, food allergies, foodborne pathogens, or conditions like gout. Provides guidance on seafood choices for vulnerable individuals and recommendations for safer alternatives.

Key Points

Pregnant and Breastfeeding Women: Must avoid high-mercury fish like shark and swordfish, choosing low-mercury options for fetal and infant development.
Young Children: Are particularly vulnerable to mercury's effects on the nervous system and should only eat low-mercury fish in appropriate portion sizes.
People with Fish Allergies: Must strictly avoid finned fish to prevent allergic reactions, which can range from mild to life-threatening.
Individuals with Compromised Immunity: Should not eat raw or undercooked seafood to minimize the risk of serious foodborne illnesses.
People with Gout: Must limit or avoid fish high in purines, such as anchovies and mackerel, to manage uric acid levels and prevent flare-ups.
Individuals on Certain Medications: Those taking blood thinners should consult a doctor, as high omega-3 intake from fish can increase bleeding risk.

While fish is a highly nutritious food, rich in protein and omega-3 fatty acids, it's not a safe dietary choice for everyone. Certain individuals must either limit their intake or completely abstain due to various health risks, including mercury contamination, allergic reactions, bacterial exposure, and high purine content. Making informed decisions about seafood consumption is critical for protecting the health of at-risk populations.

Vulnerable Populations and Mercury Contamination

Methylmercury is a neurotoxin that can accumulate in fish, particularly larger, predatory species. Exposure is especially dangerous for certain groups, as the mercury can harm the nervous system. The body can clear mercury over time, but regular consumption of high-mercury fish can lead to accumulation.

Pregnant and Breastfeeding Women

Risk: Mercury can cross the placenta and affect the fetal brain and nervous system development. It can also pass to infants through breast milk.
Recommendation: Avoid fish on the "Choices to Avoid" list, such as king mackerel, marlin, orange roughy, shark, swordfish, and bigeye tuna. Stick to low-mercury options like salmon, shrimp, and canned light tuna.

Young Children

Risk: Children's developing nervous systems are highly sensitive to the effects of mercury, which can impair cognitive development and motor skills.
Recommendation: Children under 11 should not eat high-mercury fish like shark, swordfish, or marlin. Appropriate portion sizes and low-mercury choices are recommended.

Fish and Shellfish Allergies

For those with seafood allergies, any consumption can be life-threatening. A specific protein called parvalbumin is often the cause of allergic reactions to finned fish.

Symptoms of a Fish Allergy

Hives or skin rash
Nausea, cramping, vomiting, or diarrhea
Stuffy or runny nose and/or sneezing
Anaphylaxis, a severe, potentially fatal reaction

Other Allergic-like Reactions

Scombroid Poisoning: Caused by high levels of histamine in improperly refrigerated fish like tuna or mackerel. Symptoms mimic an allergic reaction.
Anisakis Allergy: An allergy to a parasite (nematode worm) sometimes found in fish. The heat-stable allergens can trigger reactions even when the fish is well-cooked.

Compromised Immune Systems and Raw Seafood

Individuals with weakened immune systems are more susceptible to infections from foodborne pathogens, including bacteria, parasites, or viruses found in raw or undercooked seafood.

Examples of At-Risk Groups

Organ Transplant Patients: Taking immunosuppressant medication increases the risk of foodborne illness.
People with Cancer, Diabetes, or Liver Disease: These conditions can weaken the body's defenses against food pathogens.

Gout and High-Purine Fish

Purines are chemical compounds found in many foods that break down into uric acid in the body. High levels of uric acid can cause painful gout flare-ups.

High-Purine Seafood to Avoid or Limit

Anchovies
Sardines
Mackerel
Herring
Shellfish like mussels and scallops

Low-Purine Fish Options (in moderation)

Cod
Flounder
Tilapia
Tuna

Comparison of Seafood Choices for At-Risk Individuals


Risk Factor	High-Risk Seafood (Avoid)	Lower-Risk Seafood (Moderate/Safe)	Who Should Avoid/Limit?
Mercury	Shark, Swordfish, King Mackerel, Bigeye Tuna, Marlin, Orange Roughy	Salmon, Sardines, Canned Light Tuna, Shrimp, Catfish	Pregnant/Breastfeeding Women, Young Children
Allergies	Finned Fish (parvalbumin), Shellfish, Tuna/Mackerel (histamine)	Omega-3 supplements (distilled fish oil), Plant-based alternatives	Individuals with diagnosed fish or shellfish allergies
Pathogens	Raw or Undercooked Fish, Raw Shellfish	Cooked fish (internal temp 145°F), Canned or frozen fish	Individuals with compromised immunity
Gout	Anchovies, Sardines, Mackerel, Shellfish	Cod, Flounder, Tilapia, Low-fat dairy, Vegetable proteins	People with gout

Conclusion

While fish offers significant nutritional benefits, certain groups must be careful with their consumption. The potential harms of mercury accumulation, severe allergic reactions, foodborne illness from raw fish, and purine-induced gout flare-ups make it a risky food for some. Always consult with a healthcare provider for personalized dietary advice, especially if you fall into any of the vulnerable categories mentioned. Being informed and choosing seafood wisely is the best way to enjoy its benefits while staying safe.

For more information on safe seafood consumption for vulnerable populations, consult the U.S. FDA website.

How to Choose Fish Safely

Understand Risk Groups: Know if you or a family member falls into a high-risk group due to pregnancy, age, allergies, or a compromised immune system.
Prioritize Low-Mercury Options: Stick to fish from the "Best Choices" list to minimize mercury intake, especially for sensitive populations.
Avoid Raw Seafood if Immune-Compromised: Ensure all seafood is cooked thoroughly to 145°F to kill bacteria and parasites if you have a weakened immune system.
Limit High-Purine Fish for Gout: People with gout should limit or avoid high-purine fish like anchovies and mackerel to prevent flare-ups.
Check Local Advisories: For locally caught fish, check state and local advisories for potential contaminants in your area.

Frequently Asked Questions

Fish with the highest mercury levels include shark, swordfish, king mackerel, marlin, bigeye tuna, and orange roughy.

No, if you have a finned fish allergy, you should strictly avoid all types of fish. Even the steam from cooking fish can trigger a reaction in some sensitive individuals.

Raw fish can contain harmful bacteria, parasites, and viruses that can cause serious foodborne illness. Individuals with compromised immune systems are less able to fight off these pathogens and are at a higher risk of severe infection.

For most people, canned light or skipjack tuna is safe in moderation. However, due to varying mercury content, pregnant women, nursing mothers, and children should follow specific guidelines and limit intake.

People with gout should limit or avoid high-purine fish like anchovies, sardines, and herring. Lower-purine fish such as cod, flounder, and tilapia can often be included in moderation.

Fish poisoning, such as scombroid poisoning, can cause symptoms like flushing, headache, diarrhea, and vomiting, often starting within minutes to hours after consumption.

Plant-based sources of omega-3s include flaxseeds, chia seeds, and walnuts. For those with fish allergies, distilled fish oil supplements are often an option, but consult a doctor first.