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When I was a kid, the word on the playground was that holding in a sneeze would make your eyeballs pop out of your head.

It’s the kind of scare tactic that ranks somewhere between “when you swallow gum it stays in your stomach for 10 years” and “if you hit the ground in a falling dream, you die in real life.” Even at age seven, I didn’t believe it, and I still have both my eyeballs to prove it.

I’ve been a sneeze-holder my entire adult life, and I’ve always kind of thought I was doing the considerate thing by protecting those nearby from my nasal expulsions. When I can’t hold a sneeze back, I usually try to achoo into my elbow. But it’s always felt like some kind of yoga pose I’m doing wrong: Is it elbow up, face down? Am I covering my mouth, or just gesturing vaguely at my own bicep? But it turns out, although I’m unlikely to lose my eyeballs doing it, holding in a sneeze is not exactly the safe bet I once thought it was.

“The same physical principles that make sneezing an effective airway defense mechanism can, under unusual circumstances, contribute to injury when the reflex is forcibly interrupted,” Dr. Qin Liu, a researcher at Washington University in St. Louis, tells Popular Science. So just how dangerous is it to hold in a sneeze?

A sneeze is meant to go somewhere, not back into you

As chaotic and unpredictable as sneezing might seem, it’s far from random. According to Liu, sneezing evolved as a defense mechanism: a fast, forceful way to clear irritants, allergens, and pathogens out of your upper airway before they can do any damage. The force behind it is powerful, for good reason. So how does your body actually generate the force of a sneeze?

Liu offers a vivid (if somewhat terrifying) metaphor for what’s actually happening in the body during a sneeze. The diaphragm and intercostal muscles (located between the ribs) are doing the main work. “Diaphragm and intercostal muscles function as a gun, while air pressure serves as a bullet,” says Liu.

In a normal sneeze, all that built-up energy fires out through your nose and mouth, and disperses into the air. But when you block both exits by pinching your nose and clamping your mouth shut, that pressure has nowhere left to go.

“A sneeze is designed as an open pressure-release system,” Liu says. “Problems arise when that release pathway is suddenly blocked.” Instead of firing out into open air, that same force gets pushed back into your own body, into tissues and structures that are not meant to absorb it. If the pressure is strong enough, something gives.

That trapped pressure, Liu explains, can travel into your nasopharynx, your sinuses, your Eustachian tubes, even your middle ear. In rare cases, it pushes even further, into the deeper tissues of your neck or chest.

Dr. Qin Liu, a researcher at Washington University in St. Louis, compares sneezing to a gun going off. Video: What Is Sneezing? / Cleveland Clinic

None of these structures are built to absorb that kind of force. They just happen to be in the path when the pressure has nowhere else to go.

“If those forces exceed the mechanical limits of a particular structure, tissue injury may occur,” says Liu.

The result, according to Liu, can include ruptured eardrums and middle-ear barotrauma, basically, your ear bearing the brunt of pressures it was not meant to handle.

It can also cause pharyngeal injury, damage to the tissue lining your throat. In rarer cases, the consequences get more serious: cervical emphysema, where air gets trapped under the skin of your neck, sometimes causing visible swelling, and pneumomediastinum, where air leaks into the space in the chest between your lungs.

For most people, occasionally holding in a sneeze won’t land them in the emergency room. But the fact that any of this is even possible, that something as ordinary as a sneeze can, under the wrong circumstances, injure your ears, your throat, even tissues in your chest, says something about just how much force your body is generating.

When in doubt, let it out

So, holding in a sneeze isn’t really doing you any favors. But what is the best way to manage an imminent sneeze without turning it into a far-flung microbial spray-down?

According to Liu, the safest option is straightforward: let the sneeze happen, and contain it with a tissue or by sneezing into your elbow.

If letting the sneeze out fully is not an option, say, you’re mid-sentence in a job interview, or giving a eulogy, Liu recommends against blocking both exits completely. Allowing at least some airflow through your mouth can relieve some of that pressure buildup.

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Liu says there’s also a brief opportunity to prevent a sneeze before the reflex fully kicks in.

“Some people can occasionally interrupt a sneeze during its earliest stages by removing the triggering stimulus, altering their breathing pattern, pressing the tongue against the roof of the mouth, or applying mild sensory stimulation around the nose or upper lip,” she says. “These approaches may interfere with sensory processing before the reflex reaches full activation.”

But that window is small. “Once the sneeze motor program has been fully engaged, voluntary control becomes quite limited,” Liu says. In other words, once a sneeze is fully underway, your body is basically on autopilot.

“Allowing the sneeze to occur in a controlled and hygienic manner remains the safest recommendation,” she says.

So, there you have it. From now on, I’ll let my sneezes happen. My elbow and I have some practicing to do.

In Ask Us Anything, Popular Science answers your most outlandish, mind-burning questions, from the everyday things you’ve always wondered to the bizarre things you never thought to ask. Have something you’ve always wanted to know? Ask us.

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