If you weren’t surprised by this title, chances are you’ve received a chain email touting the dangers of onions. If you haven’t received this email here’s the gist: the email title is typically something alarming like “LEFTOVER ONIONS ARE POISONOUS!” and contains claims like:

  • Onions are dangerous and probably cause more cases of food borne illness than the foods we typically think of as high risk, like mayonnaise
  • Onions are bacteria “magnets”, as soon as you cut an onion it starts attracting large amounts of bacteria
  • Because of the onions’ magnetic powers, once an onion has been cut it must be thrown out if it is not used, not saved
  • Onions, when cut, can help ward off viruses, like the flu


This email has been going around for a few years, I thought perhaps it was now out of circulation but the other week I was asked by a client if the onion email was true. Nothing annoys the Nutrition Detectives more than misinformation and so I had to blog about this myth.

So, are onions a high risk food with respect to food safety and food borne illnesses? Nope.

High risk foods typically contain protein, have a high moisture content and a relatively neutral pH or slightly acidic (6.6-7.5 on the pH scale) environment. Onions do have relatively high moisture content but are not a good source of protein. They also contain sulphuric acid, the compound that makes your eyes water, which makes it highly acidic (5.3-5.8 on the pH scale) and slows the growth of bacteria. Onions actually fall in the low risk category for food borne illnesses (for a list of high and low risk foods click here).

What can make onions dangerous is how you handle them, but this is true of all foods. Cutting an onion on a cutting board you recently used to cut raw meat will cause the onion to be contaminated with harmful bacteria. But, this isn’t because the onion is high risk, it’s because of unsafe food handling practices causing cross contamination from a high risk food (raw meat) to a low risk food (onion).  There’s also no scientific basis for onions absorbing viruses or germs – that’s an old wives tale (discussed further on myth busting site, Snopes).

The onion myth? Busted. Onions are safe as long as they are handled properly.