Eating undercooked scallops can cause food poisoning from bacteria, viruses, or natural toxins that accumulate in shellfish. Most cases result in gastrointestinal symptoms like vomiting, diarrhea, and stomach cramps that resolve on their own within a few days. In rare cases, contaminated scallops can cause serious neurological problems or life-threatening infections, especially for people with weakened immune systems or liver disease.
Bacterial Infections
The most common bacterial threat in undercooked scallops is Vibrio, a group of bacteria that naturally live in coastal waters. Vibrio parahaemolyticus is one of the most frequently encountered pathogens in bivalve mollusks like scallops, clams, and oysters. Infection typically causes watery diarrhea, stomach cramps, nausea, vomiting, fever, and chills. These symptoms usually appear within 12 to 24 hours of eating the contaminated scallop and last one to three days in otherwise healthy people.
A more dangerous species, Vibrio vulnificus, can cause severe bloodstream infections with symptoms including dangerously low blood pressure, blistering skin lesions, and fever. About 1 in 5 people with a Vibrio vulnificus infection die, sometimes within a day or two of becoming ill. Some infections lead to necrotizing fasciitis, a condition where tissue around a wound dies rapidly, and limb amputation is sometimes necessary. This level of severity is rare in healthy individuals but a real danger for people with compromised immune systems, chronic liver disease, or conditions that lower stomach acid.
Norovirus From Scallops
All bivalve shellfish, scallops included, can transmit norovirus. These filter-feeding animals pull large volumes of water through their bodies, concentrating any virus present in the surrounding ocean. Cooking kills norovirus, but eating scallops that are still partially raw leaves that risk intact.
Norovirus symptoms usually appear 24 to 48 hours after exposure, though they can start as early as 12 hours. The hallmarks are projectile vomiting, severe diarrhea, and stomach pain, sometimes accompanied by fever, headache, and body aches. Most people recover within one to three days, but the intense fluid loss can be dangerous for young children, older adults, and anyone already dehydrated. Shellfish-related norovirus cases are most common from November through March, when the virus persists longer in colder marine water.
Shellfish Toxins That Cooking Won’t Destroy
Beyond bacteria and viruses, scallops can contain natural biotoxins produced by microscopic algae. These toxins are different from infections because heat does not break them down. A fully cooked scallop can still make you sick if it was harvested from waters with a toxic algal bloom. That said, undercooked scallops are riskier overall because you’re exposed to both the toxins and any live pathogens.
Paralytic Shellfish Poisoning
Paralytic Shellfish Poisoning (PSP) is caused by a neurotoxin that attacks the nervous system and paralyzes muscles. Early symptoms include tingling of the lips and tongue, which can begin within minutes of eating the scallop or take up to two hours. From there, the tingling may spread to the fingers and toes, followed by loss of muscle control in the arms and legs. In severe cases, the muscles used for breathing become paralyzed, and suffocation can occur. Death from PSP has happened in less than 30 minutes in extreme cases.
Amnesic Shellfish Poisoning
Amnesic Shellfish Poisoning (ASP) comes from domoic acid, a toxin produced by a type of algae called Pseudo-nitzschia. Milder cases cause vomiting, nausea, diarrhea, and abdominal cramps within 24 hours. More severe cases progress to neurological symptoms within 48 hours: headache, dizziness, confusion, disorientation, seizures, and short-term memory loss. The name “amnesic” is literal. Severe cases can result in permanent short-term memory loss, and in the worst outcomes, coma or death.
How to Tell if a Scallop Is Undercooked
A properly cooked scallop turns completely opaque white throughout. If you cut into one and see translucent or glassy flesh in the center, it hasn’t reached a safe temperature. The texture should have a slight bounce when pressed. FoodSafety.gov recommends cooking scallops until the flesh is “pearly or white, and opaque” rather than specifying an internal temperature the way it does for meat or poultry.
Seared scallops are popular in restaurants, and a good sear with a slightly translucent center is considered a desirable texture by many chefs. This is a conscious choice that carries some risk, similar to ordering a rare steak. The difference is that shellfish harbors a wider range of pathogens than beef, and the consequences of contamination tend to be more severe. If you’re going to eat scallops on the less-cooked side, sourcing matters. Scallops from reputable suppliers that follow shellfish safety monitoring programs are significantly less likely to carry harmful levels of bacteria or toxins.
Who Faces the Highest Risk
For a healthy adult, a bout of food poisoning from an undercooked scallop is usually unpleasant but not dangerous. The people who face genuinely serious outcomes include those with liver disease (especially from alcohol use or hepatitis), anyone on immune-suppressing medications (such as after an organ transplant or during chemotherapy), people with HIV/AIDS, pregnant women, and older adults with chronic health conditions. For these groups, a Vibrio vulnificus infection can escalate from mild symptoms to sepsis and organ failure within hours.
When Symptoms Are Serious
Most cases of scallop-related food poisoning pass within a few days with rest and fluids. But certain symptoms signal something more dangerous. The CDC considers the following signs severe enough to require medical attention: bloody diarrhea, diarrhea lasting more than three days, a fever above 102°F, vomiting so frequent you cannot keep liquids down, and signs of dehydration like not urinating much, dry mouth and throat, or dizziness when standing up. Any tingling or numbness in the lips, tongue, or extremities after eating shellfish warrants immediate attention, as these are the early signs of paralytic shellfish poisoning, which can progress to respiratory failure rapidly.