A viral article circulating since 2009 claims that placing raw, sliced onions around the home will protect the household from influenza and other diseases by "collecting" or "absorbing" any germs or viruses present. Science and common sense suggest otherwise.

An Old Wives' Tale

The National Onion Association says the idea that onions can prevent the flu is nothing more than a superstition—albeit a persistent one. It remains an established part of folk medicine, bolstered by anecdotes such as the following, which appeared in a viral email in 2009:

"FW: ONIONS FOR COLLECTING THE FLU VIRUS

In 1919, when the flu killed 40 million people, there was this Doctor that visited the many farmers to see if he could help them combat the flu. Many of the farmers and their family had contracted it and many died.

The doctor came upon this one farmer and to his surprise, everyone was very healthy. When the doctor asked what the farmer was doing that was different the wife replied that she had placed an unpeeled onion in a dish in the rooms of the home (probably only two rooms back then). The doctor couldn't believe it and asked if he could have one of the onions and placed it under the microscope. She gave him one and when he did this, he did find the flu virus in the onion. It obviously absorbed the virus, therefore keeping the family healthy."

Analysis

There's no scientific basis for this old wives' tale, which dates at least as far back as the 1500s when it was believed that distributing raw onions around a residence would protect inhabitants from the bubonic plague. This was long before germs were discovered, and the prevalent theory of the time held that contagious diseases were spread by miasma or noxious air. The (false) assumption was that onions, whose absorbent qualities had been well known since ancient times, cleansed the air by trapping harmful odors.

Lee Pearson, in "Elizabethans at Home," describes how the onions would be prepared:

"When a home was visited by the plague, slices of onion were laid on plates throughout the house and not removed till 10 days after the last case had died or recovered. Since onions, sliced, were supposed to absorb elements of infection, they were also used in poultices to draw out infection."

In the following centuries the technique remained a staple of folk medicine, and was used not only to prevent the plague but also to ward off all kinds of epidemic diseases, including smallpox, influenza, and other "infectious fevers." The notion that onions were effective for this purpose even outlasted the concept of miasma, which gave way to the germ theory of infectious disease by the late 1800s.

That transition is illustrated by passages from two different 19th-century texts, one of which claims that sliced onions are capable of cleansing a "poisonous atmosphere." The other says that onions can absorb "all the germs" in a sickroom.

Duret's "Practical Household Cookery," published in 1891, endorsed the miasma theory:

"Whenever and wherever a person is suffering from any infectious fever, let a peeled onion be kept on a plate in the room of the patient. No one will ever catch the disease, provided the said onion be replaced every day by one freshly peeled, as then it will have absorbed the whole of the poisonous atmosphere of the room, and become black."

Meanwhile, an article published in the Western Dental Journal in 1887 endorsed the germ theory:

"It has been repeatedly observed that an onion patch in the immediate vicinity of a house acts as a shield against the pestilence. Sliced onions in a sick room absorb all the germs and prevent contagion."

There is, of course, no more scientific basis for the belief that onions absorb all the germs in a room than there is for the belief that onions rid the air of "infectious poisons." Viruses and bacteria can become airborne via droplets of saliva or mucus when people cough or sneeze, but they don't, generally speaking, hover in the atmosphere like gases and odors. By what physical process—other than magic—is this "absorption" supposed to take place? The myth of the cleansing onion has been thoroughly debunked.