Eating undercooked salmon can expose you to parasites, bacteria, and in some cases histamine toxins that cause reactions ranging from mild food poisoning to serious infections. Most healthy adults recover within a few days to a week, but the experience can be genuinely miserable, and certain groups face much higher stakes.
Parasites You Can Get From Undercooked Salmon
Two parasites are the standout concerns with salmon that hasn’t been fully cooked: roundworms and tapeworms.
Anisakis roundworms are the more common threat. When you eat a live larva in undercooked fish, it can burrow into the lining of your stomach or intestines. Symptoms include abdominal pain, nausea, vomiting, diarrhea, and sometimes blood or mucus in your stool. Some people also develop allergic reactions like rashes and itching, and in rare cases, a severe allergic reaction called anaphylaxis. One distinctive sign: you may feel a tingling sensation in your mouth or throat while eating, which is actually the worm moving. If that happens, you can sometimes cough up or manually remove the larva before it reaches your stomach.
Fish tapeworms are the largest tapeworms that infect humans and can grow up to 30 feet long inside your intestines. Salmon is a known carrier. Many people with a tapeworm infection have no symptoms at all for weeks or months, while others experience abdominal discomfort, diarrhea, fatigue, or vitamin B12 deficiency from the worm absorbing nutrients. The infection is treatable with medication, but it can persist for years if you don’t realize you have it.
Bacterial Food Poisoning
Undercooked salmon can also harbor harmful bacteria, with Salmonella and Listeria being the most relevant to fish.
Salmonella infection typically shows up 6 hours to 6 days after eating contaminated food. You’ll experience diarrhea, fever, and abdominal cramps that generally last a few days to a week. Diarrhea can linger for up to 10 days, and it may take several months before your bowel habits fully return to normal. Most people recover without medical treatment, but severe dehydration from prolonged diarrhea can land you in a hospital.
Listeria is less common but more dangerous. It’s specifically associated with refrigerated smoked seafood, like cold-smoked salmon or lox. In healthy people, it causes fever and diarrhea. But in vulnerable individuals, the bacteria can spread beyond the gut, causing stiff neck, confusion, loss of balance, and convulsions. Listeria has a longer incubation period than most foodborne bacteria, sometimes taking weeks to cause symptoms, which makes it harder to trace back to a specific meal.
Histamine Poisoning From Improperly Stored Salmon
This one catches people off guard because it’s not really about cooking temperature. When salmon sits at temperatures above 40°F (4°C) for too long, bacteria on the fish convert a naturally occurring amino acid into histamine. Properly stored fish contains negligible histamine, but contaminated fish can have levels 200 to 500 times higher. The result mimics a severe allergic reaction: flushing, headache, stomach cramps, diarrhea, and sometimes hives or a rapid heartbeat.
The tricky part is that cooking doesn’t destroy histamine. Once it’s built up in the fish, no amount of heat will make it safe. Symptoms usually appear within minutes to a couple of hours and resolve on their own or with antihistamines. The best prevention is keeping salmon properly refrigerated from the moment it’s caught to the moment it’s cooked.
Why Pregnant People Face Higher Risks
For most healthy adults, undercooked salmon means a rough few days. For pregnant people, the consequences can be far more serious. Foodborne infections during pregnancy carry an increased chance of pregnancy loss, preterm delivery (birth before 37 weeks), or direct infection of the newborn. High fever from any food poisoning also raises risks to the developing baby.
Listeria is the biggest concern. Newborns with Listeria infection can develop sepsis or meningitis, a swelling around the brain and spinal cord that can lead to long-term developmental problems if not treated quickly. People with weakened immune systems face similar risks of severe, invasive infection from bacteria that healthy adults typically fight off without difficulty.
How to Tell if Your Salmon Is Undercooked
Properly cooked salmon reaches an internal temperature of 145°F (62.8°C). If you don’t have a thermometer, there are reliable visual cues. Raw salmon is bright orange and translucent. As it cooks, the color shifts to a lighter, opaque pink, and white streaks of protein begin appearing on the surface of the flesh. The most dependable test is the fork test: press a fork into the thickest part of the fillet and twist gently. If the fish flakes apart easily with little resistance, it’s done. Undercooked salmon will feel dense and resist separating.
If white protein is visibly seeping from the sides of the fillet, the interior is cooked through. On the other hand, if that protein has dried out and the fat is pooling on the surface, you’ve overcooked it.
What About Sushi-Grade Salmon?
Salmon served raw in sushi restaurants isn’t free of parasites by nature. It’s made safe through freezing. The FDA recommends that fish intended for raw consumption be frozen at -4°F (-20°C) for at least 7 days, or flash-frozen at -31°F (-35°C) until solid and then stored for at least 15 hours. These temperatures kill parasites that cooking would otherwise destroy. Your home freezer may not reach these temperatures consistently, so freezing salmon at home isn’t a guaranteed substitute for proper commercial processing.
Farmed salmon is sometimes perceived as lower risk for parasites than wild-caught, since farmed fish eat controlled feed rather than smaller infected prey. However, farmed fish can still carry parasites and bacteria, and the distinction isn’t reliable enough to treat farmed salmon as inherently safe to eat raw without proper freezing.
What to Do if You Already Ate It
If you’ve eaten salmon that you suspect was undercooked, don’t panic. The majority of cases result in either no symptoms or mild food poisoning that resolves on its own. Watch for nausea, vomiting, diarrhea, abdominal pain, or fever over the next several hours to days. Stay hydrated, especially if diarrhea develops, since dehydration is the most common complication of foodborne illness.
Seek medical attention if you experience a high fever, bloody stool, signs of an allergic reaction (widespread rash, difficulty breathing, swelling), or symptoms that last more than a few days without improving. If you’re pregnant, immunocompromised, or notice neurological symptoms like confusion or blurred vision, get evaluated promptly. Parasitic infections like tapeworms may not produce obvious symptoms right away but are easily treated once diagnosed, so mention the exposure to your doctor if unusual digestive symptoms develop weeks later.