Eating raw tuna is generally safe when the fish has been handled, frozen, and stored properly. Millions of people eat it in sushi and sashimi every week without incident. But raw tuna does carry real risks, including parasites, bacteria, histamine poisoning, and mercury exposure, and how dangerous those risks are depends largely on the quality of the fish and how it was treated before it reached your plate.
What “Sushi-Grade” Actually Means
There is no FDA-regulated definition of “sushi-grade” or “sashimi-grade” tuna. These are marketing terms, not legal standards. What the FDA does require is that fish intended for raw consumption be frozen to kill parasites. The specific guidelines call for one of three protocols: freezing and storing at -4°F (-20°C) or below for 7 days, freezing at -31°F (-35°C) or below until solid and holding at that temperature for 15 hours, or freezing at -31°F (-35°C) until solid and then storing at -4°F (-20°C) for 24 hours.
Reputable sushi restaurants and fish suppliers follow these freezing protocols as standard practice. The tuna you eat at a sushi bar has almost certainly been flash-frozen at sea or at a processing facility, which is why it’s safe to eat raw. A home freezer, which typically runs around 0°F, is not cold enough to reliably kill parasites within the FDA’s recommended timeframes. So buying a random tuna steak from the grocery store and eating it raw is riskier than ordering from a restaurant with a proper supply chain.
Parasites in Raw Tuna
Tuna can harbor parasitic roundworms from the Anisakis family. These larvae live in the flesh of many ocean fish species, and their prevalence varies by geographic fishing ground and season. If you swallow a live Anisakis larva, it can burrow into the lining of your stomach or intestines, causing sharp abdominal pain, nausea, and vomiting, sometimes within hours of eating. The condition, called anisakiasis, usually resolves when the worm is removed (often during an endoscopy), but it’s unpleasant.
Proper freezing kills these parasites completely. That’s the entire reason the FDA’s freezing guidelines exist. If your raw tuna was frozen according to commercial standards before serving, the parasite risk is essentially eliminated. The risk comes from eating fresh, never-frozen wild tuna that hasn’t been inspected.
Bacterial Contamination
Bacteria are a more common threat than parasites. Raw tuna has been linked to outbreaks of Salmonella, most notably a 2019 multistate outbreak of Salmonella Newport traced to frozen ground tuna imported from Vietnam. In that outbreak, every person who provided details about what they ate had consumed raw tuna or spicy tuna rolls at restaurants.
Bacterial contamination typically happens during processing, grinding, or handling rather than in the fish itself. Ground tuna products (like the spicy tuna mix used in many sushi rolls) carry higher risk because grinding exposes more surface area to bacteria and mixes any contamination throughout the product. Whole cuts of raw tuna are somewhat safer in this regard.
Bacteria grow rapidly between 40°F and 140°F. Raw tuna left at room temperature for more than 2 hours should be discarded. In the refrigerator, raw tuna lasts only 1 to 2 days before it should be used or frozen.
Histamine Poisoning: The Hidden Risk
Tuna is especially prone to a type of food poisoning that has nothing to do with bacteria you’d normally worry about. When tuna isn’t kept cold enough, certain bacteria convert an amino acid in the fish’s flesh into histamine. Once histamine builds up, no amount of cooking or freezing will destroy it. Eating the fish triggers symptoms that look like a severe allergic reaction: facial flushing, headache, rapid heartbeat, abdominal cramps, and sometimes hives or swelling.
This is called scombroid poisoning (named after the scombroid fish family that includes tuna and mackerel). Research shows that tuna stored at 86°F (30°C) can reach dangerous histamine levels in just 2 days, while even moderately cool temperatures of 64°F (18°C) allow dangerous levels to build within 4 days. Only consistent refrigeration at 40°F (4°C) or below prevents histamine formation entirely. The takeaway: the cold chain matters more than almost anything else when it comes to raw tuna safety. A fish that was left on a warm dock for too long before being iced can be dangerous even if it’s later handled perfectly.
Mercury Levels by Tuna Species
Mercury is a long-term concern rather than an immediate one. All tuna contains some mercury because it accumulates in predatory fish over their lifetimes, but the amount varies dramatically by species. FDA testing data shows mean mercury concentrations in parts per million (ppm) for common types:
- Skipjack tuna: 0.144 ppm (the lowest, used in most canned “light” tuna)
- Yellowfin (ahi) tuna: 0.354 ppm (common in sushi restaurants)
- Bigeye tuna: 0.689 ppm (often served as premium sashimi)
Bigeye tuna has nearly five times the mercury of skipjack. If you eat raw tuna regularly, choosing yellowfin or skipjack over bigeye significantly reduces your mercury exposure. For most healthy adults, eating raw tuna a few times per week is fine from a mercury standpoint. The concern increases with frequency: daily consumption of high-mercury species like bigeye can push you toward levels that affect the nervous system over time.
Pregnant or breastfeeding women and young children are more vulnerable to mercury’s effects on brain development. Federal guidelines recommend these groups eat 8 to 12 ounces of low-mercury seafood per week while avoiding the highest-mercury options. Bigeye tuna falls into the “limit” category, while skipjack is considered a good lower-mercury choice.
How to Tell if Raw Tuna Has Gone Bad
Fresh, safe raw tuna should smell like the ocean, clean and mildly briny. Spoilage follows a predictable pattern. First, the fish loses its characteristic smell and taste, becoming bland and neutral. Then off-odors develop: a “fishy” smell (caused by a compound called trimethylamine that bacteria produce), followed by sour or fruity notes, and eventually ammonia and sulfur smells. If your raw tuna smells noticeably fishy, sour, or like ammonia, it’s past the point of safe raw consumption.
Color is trickier. Fresh tuna ranges from deep red to pink depending on the species and cut. Brownish or dull coloring can indicate oxidation, but some tuna is treated with carbon monoxide gas to keep it looking bright red longer. This means color alone isn’t a reliable freshness indicator. Trust your nose over your eyes, and pay attention to the texture. Fresh raw tuna should feel firm and spring back slightly when pressed. Mushy, slimy, or sticky flesh is a sign of spoilage.
Who Should Avoid Raw Tuna
Certain groups face higher stakes from the bacteria and parasites that can come with raw fish. People with weakened immune systems, whether from HIV, chemotherapy, organ transplant medications, or other conditions, are more likely to develop severe illness from the same pathogens a healthy person might fight off easily. Young children, adults over 65, and pregnant women also fall into this higher-risk category. For these groups, the safest approach is to eat tuna cooked to an internal temperature of 145°F, which eliminates both bacterial and parasitic risks entirely.
For everyone else, the practical advice is straightforward: buy from reputable sources that follow proper freezing and cold-chain protocols, eat raw tuna within a day or two of purchase, and never eat raw tuna that’s been sitting at room temperature. The vast majority of raw tuna sold through established sushi restaurants and quality fish markets has been handled safely. The risk isn’t zero, but for healthy adults eating properly handled fish, it’s low.