Hits and myths

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it has long been thought that leftover onions are a magnet for bacteria and viruses. As far back as the 1500s, raw onions were placed in and around homes all over Europe, in the belief that they prevented diseases - including bubonic plague - by absorbing the "elements of infection". The Chinese, Ancient Greeks, and Native Americans, used onions to ward off infections and relieve respiratory congestion.

Today, because raw onions are thought to attract bacteria, it is assumed that one should never keep half an onion, not even in the fridge, because it can spread illnesses like colds and flu. Based on this belief, many people avoid eating leftover onions.

This ancient folklore might stem from the fact that raw onions contain compounds that kill or inhibit bacteria when ingested, says associate professor Lee Yuan-kun from the Department of Microbiology at the National University of Singapore. One such compound, allicin is thought to have anti-fungal properties, while quercetin, a bioflavonoid, has been found to be anti-fungal as well as anti-bacterial.

However, there is no scientific evidence that cut onions, when placed around the house, are a flu remedy. In the first place, bacteria and viruses do not "fly around" from surface to surface. They are transported by contact - that is, if you cut contaminated meat and then use the same, unwashed knife to chop vegetables, bacteria will be transferred from the meat to the vegetables.