Can you blow out a candle with your mask on?
That question became … a thing … this month when Bill Nye (aka “The Science Guy”) made a TikTok.
In it, he dons various types of masks that people are using during the pandemic, as he puts it, to “prevent particles from my respiratory system from getting into the air and then into your respiratory system” — in other words, a way of limiting transmission of viral particles. Nye attempts to blow out a candle about a foot away — a simulation for everyday respiratory exchanges and interactions such as coughs and conversations.
Most of his masks do the job (except for a knitted scarf), though in other versions of this experiment and in tests conducted by NPR mask wearers, a bandanna over the mouth usually allowed the wearer to extinguish the flame.
Basically, you want the flame to stay lit, says Amy Price, a senior research scientist at Stanford University’s Anesthesia Informatics and Media Laboratory. Otherwise, it can be a sign that the mask isn’t acting as a strong enough barrier. If you can blow out the flame easily while wearing a mask, she says, there’s too much air exchange between you and the outside world.
Still, she cautions that the test isn’t foolproof. Outside variables, such as the type of candle and your personal lung strength can affect the outcome. So take your results with a big, big grain of salt, Price says.
Abraar Karan, a physician at Harvard Medical School, notes: “Being able to blow a candle out may be some measure of how well particles can exit your mask, [but it’s] unclear to me how reliable that is as a proxy for small aerosols exiting with normal speaking or coughing.”
Nonetheless, Price says she believes the candle test can be a good way to suss out the masks that are clearly not doing their job — the dead giveaway cases.
“It’s an OK rule of thumb,” she says. “It isn’t scientific, but it’s a pretty good estimate, especially when you combine it with other [tactics] and recommendations” regarding mask quality.