If the social media rumors are true, your leftover rice may be trying to kill you. Experts on the matter, however, tell a somewhat different story.
It’s true that cooked rice left at room temperature too long can become a happy home to intruders, notably Bacillus cereus, a common type of bacteria that lives in soil and, therefore, in much of the food we eat. “B. cereus loves to grow in the warm and moist environment provided by cooked rice,” said Si Ming Man, a professor in the division of immunology and infectious diseases at the Australian National University.
What has made B. cereus more TikTok-famous than other food-borne bugs is that its spores are hardy enough to survive the cooking process, and then — when food isn’t kept cool in the refrigerator — can grow and produce toxins that even vigorous reheating won’t destroy, Dr. Man said. And yes, while the illness is sometimes referred to as “reheated rice syndrome,” since leftover rice is a common pathway, other foods (steak, pasta salad, milkshakes) have prompted B. cereus outbreaks. (The case that recently went viral on TikTok was caused by spaghetti left at room temperature for five days in 2008 — definitely don’t do that.)
So what about the countless batches of leftovers you’ve zapped (or even eaten cold) over the years, without a trip to the hospital? Martin Wiedmann, a food safety professor at Cornell University, said the reason we hear relatively little about those cases was because “the disease is typically very mild, unlike other food-borne diseases.” Symptoms show up in one of two unpleasant ways — primarily vomiting or diarrhea — but both usually resolve on their own within 24 hours.
“The illness is likely to be over by the time you are inspired to do something about it,” said Linda J. Harris, a professor at the University of California, Davis, who researches microbial food safety. “The exception,” she added, “is for those people who might have weakened immune systems” — children younger than 5, adults 65 and older, and pregnant and other immunocompromised people. But experts agree that even healthy people have good reason to follow the simple, common-sense guidelines below.