What happens if you eat raw tuna? A comprehensive guide to risks and safety

November 14, 2025 •

4 min read

A study found that up to 89% of tuna from certain waters can be infected with parasites. So, what happens if you eat raw tuna without taking proper precautions? While it can be a healthy food, consuming it raw poses several health risks, including parasitic infections, bacterial illness, and mercury contamination.

Quick Summary

Eating raw tuna carries risks like parasites, bacteria, and mercury. Safety hinges on proper freezing and sourcing from reputable suppliers, with certain groups advised to exercise greater caution.

Key Points

Parasitic Risk: Raw tuna, especially wild-caught, can contain parasites like Anisakis, causing gastrointestinal illness unless properly frozen.
Bacterial Contamination: Raw fish can harbor bacteria such as Salmonella and Vibrio, leading to food poisoning if not handled hygienically.
Mercury Exposure: Larger tuna species like bigeye and albacore contain high levels of mercury, a neurotoxin that accumulates with frequent consumption.
Scombroid Poisoning: Improper chilling of tuna can lead to a build-up of histamine, causing an allergic-type reaction that is not eliminated by cooking.
FDA Freezing Standards: Reputable suppliers follow FDA guidelines for freezing fish intended for raw consumption, a critical step for killing parasites.
Vulnerable Groups: Pregnant women, young children, older adults, and immune-compromised individuals should avoid raw tuna due to increased health risks.
Moderation is Key: Enjoying raw tuna in moderation and sourcing from trustworthy vendors are the best ways to mitigate health risks.

The Potential Dangers of Eating Raw Tuna

While consuming raw tuna in the form of sushi or sashimi is a global culinary tradition, it is not without risks. The ocean environment, the food chain, and handling procedures all play a role in determining the safety of raw fish. There are three primary health concerns associated with eating raw tuna: parasitic infections, bacterial contamination, and exposure to heavy metals like mercury. Understanding these risks is the first step toward enjoying raw seafood responsibly.

Parasitic Infections

Raw tuna, particularly wild-caught varieties, can harbor parasites that can cause foodborne illness in humans. The most common parasitic infection from raw fish is Anisakiasis, caused by nematode larvae (roundworms) of the Anisakis genus. When ingested, these parasites can embed themselves in the walls of the esophagus, stomach, or intestines, leading to symptoms such as abdominal pain, nausea, and vomiting. Though the worms cannot survive long-term in a human host, their presence can cause significant discomfort and, in rare cases, severe allergic reactions.

Anisakiasis: Symptoms include severe abdominal pain, nausea, vomiting, and a mild fever. In some instances, a tingling sensation in the mouth or throat may occur as the worm attempts to embed itself.
Kudoa Parasites: Certain species of Kudoa have been linked to food poisoning in humans, causing diarrhea and other gastrointestinal distress.

Proper freezing methods, as recommended by the U.S. Food and Drug Administration (FDA), are effective at killing these parasites. The term "sushi-grade" often implies the fish has undergone this freezing process, though it is an unregulated industry term and relies on the supplier's reputation.

Bacterial Contamination

Even with modern handling, raw fish can be a vehicle for harmful bacteria. While cooking destroys most bacteria, raw preparation leaves an opening for infection. Common culprits include Salmonella, Vibrio, and Clostridium.

Salmonella: Can cause food poisoning with symptoms like diarrhea, fever, and abdominal cramps.
Vibrio: Found in coastal waters, this bacterium can lead to symptoms such as watery diarrhea, abdominal cramping, nausea, vomiting, and fever. It is particularly dangerous for individuals with weakened immune systems.

Thorough cooking is the most reliable way to eliminate these bacteria, but strict hygiene practices are crucial for preventing cross-contamination during raw preparation.

Mercury Exposure

Mercury is a heavy metal that accumulates in ocean waters and is absorbed by marine life. Tuna, being a large predatory fish at the top of the food chain, can contain high levels of methylmercury. Larger species, including albacore, yellowfin, bluefin, and bigeye, tend to have higher concentrations than smaller ones. Regular or excessive consumption of mercury can lead to neurotoxicity, causing symptoms like memory loss, tremors, and numbness.

Scombroid Fish Poisoning

Another specific type of foodborne illness linked to tuna is scombroid poisoning. This occurs when histidine-rich fish, such as tuna, are not properly chilled after being caught. Bacteria can then convert a natural substance in the fish into high levels of histamine. This toxin is heat-resistant, meaning it is not destroyed by cooking. Symptoms, which resemble an allergic reaction, can appear within an hour and include flushing, headache, itching, and heart palpitations.

Raw Tuna vs. Cooked Tuna: Risks and Benefits


Factor	Raw Tuna	Cooked Tuna
Risks	Higher risk of parasites, bacteria (if not handled properly), and scombroid poisoning.	Lower risk of parasites and bacteria due to heat treatment. Retains mercury levels.
Mercury Content	Varies by species and size; high in large predatory species.	Cooking does not reduce mercury content.
Nutritional Value	Higher concentration of omega-3 fatty acids, vitamins, and minerals.	May have slightly reduced omega-3s depending on cooking method.
Flavor & Texture	Preferred for its delicate, buttery flavor and smooth texture in dishes like sushi and sashimi.	Flavor and texture change dramatically; can become dry and firm if overcooked.
Safety Precautions	Requires proper freezing and handling to kill parasites and minimize bacterial growth.	Cooking to an internal temperature of 145°F kills most pathogens.

How to Safely Enjoy Raw Tuna

If you choose to enjoy raw tuna, following these guidelines can help minimize the risks involved:

Source from Reputable Suppliers: Only purchase tuna from trusted fishmongers or restaurants known for their strict adherence to food safety protocols. Ask about their handling and freezing procedures.
Verify "Sushi-Grade" Status: While not a regulated term, a reputable supplier will be knowledgeable about the sourcing and handling of their fish. For home preparation, ensure the fish was properly flash-frozen to kill parasites.
Maintain Cold Temperatures: Keep raw tuna properly refrigerated on ice or in the coldest part of your fridge. Never leave it at room temperature for an extended period.
Practice Strict Hygiene: Use separate cutting boards and utensils for raw fish to prevent cross-contamination. Wash hands thoroughly before and after handling.
Limit Consumption: Due to mercury levels, especially in larger species like bigeye and bluefin, moderate your intake. The FDA offers guidelines on safe consumption levels.
Know Your Risks: Vulnerable groups, including pregnant women, young children, older adults, and those with compromised immune systems, should avoid raw tuna completely.

Conclusion

Eating raw tuna is a delectable experience enjoyed worldwide, but it is not without genuine health risks. From parasitic infections and bacterial contamination to the long-term effects of mercury exposure, the dangers are real but largely manageable. The key to safe consumption lies in three main principles: moderation, sourcing from reputable and knowledgeable suppliers who follow proper freezing protocols, and diligent handling practices at home. Understanding these aspects allows you to make informed decisions and appreciate this food safely. For more detailed food safety information, consult official resources like the FDA. FDA Guidelines for Seafood

Frequently Asked Questions

No, 'sushi-grade' is a marketing term used by the seafood industry and is not regulated by the FDA. It generally implies the fish has been handled and frozen in a way considered safe for raw consumption, but it relies on the reputation of the seller.

Symptoms can vary depending on the pathogen but may include abdominal pain, nausea, vomiting, fever, and diarrhea. For parasites, symptoms may involve a tingling throat or intense stomach discomfort.

No, cooking does not remove or reduce the mercury content in tuna. The mercury has already been absorbed into the fish's tissues. The best way to limit mercury exposure is to consume high-mercury species in moderation.

Fresh, high-quality tuna should have a mild, clean ocean smell, not a strong fishy or sour odor. The flesh should be firm, vibrant, and translucent, not dull, discolored, or mushy.

Individuals with weakened immune systems, pregnant or breastfeeding women, older adults, and young children are at a higher risk of foodborne illnesses and mercury exposure, and should therefore avoid raw tuna.

Canned tuna is cooked during processing, which eliminates the risk of parasites and bacteria. Canned light tuna from smaller species also generally contains lower mercury levels than raw albacore or bigeye tuna.

A standard home freezer may not reach the temperatures required to kill all parasites. The FDA recommends freezing at -4°F for 7 days or at -31°F until solid for 15 hours. It is safer to purchase properly handled, pre-frozen tuna from a reputable source.