It turns out that your eating habits could really harm your health—sometimes without you realizing it until it’s too late.
While experts agree on the benefits of fresh, whole foods, there’s a cautionary note from a food policy professor. The grocery store’s produce section may hide some dangers.
Not every fruit and vegetable is the same, and those convenient pre-packaged meals can carry hidden risks of contamination.
“Pre-washed bagged greens are among the most dangerous products found in grocery stores,” says Darrin Detwiler, a food policy professor at Northeastern University and author of “Food Safety: Past, Present, and Forecast.”
He points out that bagged salads have been tied to numerous foodborne illness outbreaks, which can lead to serious consequences—hospital stays, kidney failure, or worse.
These pre-packaged salads may contain harmful pathogens such as Listeria, Salmonella, and E. coli, all of which raise their contamination risk considerably, marking them as some of the worst offenders in food safety.
The Centers for Disease Control and Prevention list symptoms from food poisoning—like nausea, vomiting, fever, abdominal pain, and diarrhea—often resulting from bacteria like Listeria and E. coli.
According to a 2024 report from the Journal of Foodborne Infections, leafy greens contribute to about 9.2% of foodborne diseases caused by known pathogens in the United States, leading to over 2.3 million illnesses annually.
What makes these leafy vegetables particularly vulnerable is that they’re typically eaten raw, which means heat (that could kill bacteria) doesn’t come into play before they reach consumers.
Contamination can happen at various stages of production. Pathogens can be introduced during harvesting from contaminated water, soil, or air, or due to contact with animals. For example, lettuce might be grown near livestock operations, increasing the risk of E. coli or Salmonella contamination through tainted irrigation water.
Detwiler highlights that large pits and fertilizer lagoons can also be major contamination sources. “Pathogens from these lagoons can seep into irrigation systems, spreading deadly bacteria like E. coli into fields,” he notes.
Once harvested, lettuce can still be compromised through handling, dirty equipment, or the water used to clean it. The processing of greens from various farms in centralized facilities means that just one infected leaf could compromise thousands of bags across several states.
“When greens are mixed, washed, and packaged together, the risk extends widely,” Detwiler explains.
This industrial washing process can inadvertently spread bacteria as well. Greens must be kept cold to inhibit pathogen growth—if not maintained at proper temperatures throughout the supply chain, bacteria can flourish and infect food before it reaches supermarket shelves.
Importantly, freezing doesn’t kill these bacteria; it only slows down their growth. Washing greens might not be effective in eliminating pathogens, and, in fact, could introduce more contamination from tools and surfaces that are themselves not clean.
When it comes to leafy greens, it’s wise to choose carefully.
Detwiler recommends steering clear of bagged options altogether, opting instead for whole heads of lettuce or loose bundles, as these have less surface area for contamination. Just be sure to rinse them under cold running water.
For those who do choose bags, he suggests inspecting for wet, slimy, or discolored greens and avoiding those that come in damp packaging—these could be signs of improper storage.
Moreover, try to keep greens from experiencing significant temperature fluctuations. Keeping them in hot conditions or at room temperature can create a breeding ground for bacteria.
Lastly, buy only the amount you plan to use in the next couple of days, and always check for recalls and expiry dates.
