Onions in reasonable quantities are not considered harmful – apart from the foul breath you get from eating them – but health experts warn that such videos promote a blind belief in simple home remedies that could compromise public health.

“Onions aren’t going to hurt anybody, but if somebody is sick, they should seek actual medical attention,” says Katrine Wallace, an epidemiologist and assistant professor at the University of Illinois Chicago.

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“I am afraid that people will just drink onions and not seek medical care [and] they could spread Covid or the flu in the community.”

The pseudoscience has found many takers, with comments under the videos filled with declarations like “this worked for me!”

That, Wallace said, suggested the so-called “placebo effect”, with the dubious onion treatment getting the credit after the virus naturally ran its course.

In one of the most popular TikTok videos, which garnered over 2.5 million views, one woman – whose profile did not mention her qualifications and described her only as a “child of mother nature” – zealously promoted onion water.

For greater healing effects, she implored her viewers to ferment the concoction for hours to make it more “potent”.

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“We love a miracle cure and, for some reason, we seem to think that the more painful a remedy is to consume, the more magic it will work,” says Abbie Richards, a disinformation researcher.

“Simple solutions for complex problems frequently perform well in engagement-driven algorithms like TikTok’s, particularly when those solutions are cheap and accessible in areas where evidence-based healthcare is not.”

A TikTok spokesman said the platform removes content that qualifies as medical misinformation that is “likely to cause significant harm”.

The onion water videos, he added, did not cross that threshold of “significant harm” and were therefore left untouched.

That approach, many experts say, underscores the challenge facing social media platforms of finding ways to eliminate misinformation without giving users the impression that they were trampling on free speech.

Richards cautioned that “excessive moderation” in the case of onion water videos could backfire and “encourage narratives that the truth of affordable medicine is being intentionally hidden”.

A more effective approach, she said, would be for TikTok to ensure accurate health information is “available, accessible and engaging”.

“Whether TikTok should take down videos about benign but useless remedies, that’s not for me to say,” says Valerie Pavilonis, an analyst at the misinformation watchdog NewsGuard.

“Still, even if a supposed remedy like drinking onion water to solve sinus problems doesn’t directly hurt you, it could make you wrongly think that you are treating the problem”.

The popularity of the videos reflected what Richards called “systemic failures” in healthcare.

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In a country with expensive medical care, data from the US Centres for Disease Control and Prevention shows roughly 30 million Americans, or nine per cent of the population, have no health insurance.

Millions of other Americans are “underinsured”, with their coverage not providing them affordable healthcare, according to the non-profit organisation Commonwealth Fund.

“It’s very easy for us to say: ‘Remember to talk to your doctor about medical treatments’,” Richards said. “But I would expect that a society with limited access to healthcare, an overburdened healthcare system, and a generally confused approach to the newest wave in illness might start drinking onion water or putting garlic in their ears.”