Myth Busted: Onions on Feet Don't Cure Illness

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Updated September 16, 2018

A viral message making the rounds on social media claims that placing sliced raw onions on the bottom of your feet and securing them with socks before going to bed will "take away illness" overnight—supposedly because the onions absorb toxins from the body. Some also say that this remedy prevents the flu.

The Truth About Onions

Strapping raw onions to your feet probably won't do you any harm as long as it isn't a substitute for proper medical care, but there's no scientific reason to believe it will cure what's ailing you, either.

The claim that onions are "toxin absorbers" is pseudo-scientific nonsense, as is the related claim that you should never save a leftover onion because "it will absorb all the toxins in the air of your refrigerator." This is a revised version of an older myth to the effect that "onions are a magnet for bacteria," and that therefore it's not even safe to store them in a zip-lock bag.

That's just plain false, says Joe Schwarcz of McGill University's Office for Science and Society. "The fact is that onions are not especially prone to bacterial contamination," he writes. "In fact, quite the opposite." According to Schwarcz, it's no more dangerous to eat cut onions stored properly in a refrigerator than it is to eat any other raw vegetable stored for an equal length of time.

This is reaffirmed by Dr. Ruth MacDonald, Professor of Food Science and Human Nutrition at Iowa State University. "No, onions do not absorb bacteria," MacDonald says.

"The idea that a vegetable would attract and suck into itself bacteria from the air is not even logical. The onion may turn black because it would eventually rot from both cell breakdown events and bacterial contamination if you left it out, not because it absorbs germs."

And not because it absorbs so-called "toxins," either. We have not found a single scientific source stating that onions absorb "toxins" of any kind, much less those specifically related to diseases.

A Bit of History

It's true that 500 years ago people believed that strewing onions around the home protected against the plague, but there are two important caveats to bear in mind: one, this belief was based on an ignorance of what actually causes infectious diseases and how they spread; and two, the theory behind it wasn't that onions absorb germs or "toxins," but rather that onions absorb noxious odors (miasmas), which were thought at the time to be the main vehicles of contagion.

The miasma theory began to lose steam as medical science progressed in the latter half of the 19th century, but we still find sources like "The People's Physician," a home medical manual published in 1860, stating that raw onions "possess the property of imbibing the morbid effluvia, or noxious exhalations from persons diseased." A few sentences later the author makes this now-familiar recommendation:

"Persons threatened with or having seated fevers, should have the half of a raw onion bound upon the sole of each foot at bedtime, being permitted to remain until morning, by which time the slices will have drawn, to a great extent, the febrile disorder from the system."

By the 1880s, references to "morbid effluvia" and "noxious exhalations" were giving way to talk of germs and bacteria, but the onion remedy still held sway in some quarters, as in this 1887 example from the "Western Dental Journal": "Sliced onions in a sick room absorb all the germs and prevent contagion."

Now, more than 125 years later, we read on Facebook that onions cure disease by absorbing "toxins," as if this is a long-established medical fact.

Regardless of whether the agent of infection is thought to be a miasma, germ, or toxin, what none of these sources provides is a scientific explanation of how the humble onion could be capable of performing such an incredible absorptive feat. So far as we've been able to discover, there isn't one.