Although some TikTokers claim that slicing an onion over their heads will kill viruses and “draw in the poison,” this is not supported by scientific evidence.

The question: “What do you do with onions?” On October 23rd, @Poshmamma,
aka the “onion woman” of TikTok, posed this question to her audience. “You
may clean the air in your home simply by cutting them up and placing them
in strategic locations about the house. They will absorb harmful gases and
particles like dust, pollen, pet dander, mold, and viruses. They are highly
effective at preventing illness in the home.”
She went on to say, “If other people are becoming sick in your house,” to
“draw in the disease and draw in the poison,” one should “go to the grocery
shop and get the red onions.”