People’s sneezing tendencies can be almost as individual as their fingerprints. Some produce earth-shattering blasts. Others emit delicate “ahchoos!” But why do we sneeze in the first place? No matter where you fall on the sneezing spectrum, the answer is more interesting than you might expect and will leave you pretty impressed with your body.
Sneezing helps to clear unwelcome stuff from your nose.
As one entrance to your complex respiratory system, your nose has the important job of humidifying, warming, and filtering the air you breathe, according to the Merck Manual. That makes your nose one of the first lines of defense for keeping potentially harmful particles out of your lungs, Erich Voigt, M.D., clinical associate professor and chief of general/sleep otolaryngology at NYU Langone Health, tells SELF. Your nose is lined with mucous membranes that constantly trap pathogens and debris. Cilia, microscopic hairlike protrusions lining your nose, can channel this dirty mucus to the front of the organ (or down your throat).
But sometimes something triggers your nose intensely enough that your body wants to expel it forcefully and immediately, so this ordinary cleansing process gets an instant boost in the form of a sneeze. “The sneeze serves as a mechanism to clean the nose” and stimulate the cilia to keep things moving along, Michael Benninger, M.D., chairman of the Cleveland Clinic Head & Neck Institute, tells SELF. “It’s basically rebooting the nose,” he says.
The sneeze reflex is usually activated when your nose’s mucous membranes are irritated.
Sometimes it can happen if your throat is irritated, too. Either way, sneezing is “a well-coordinated action involving a lot of muscles and nerves beginning with a trigger,” Dr. Voigt explains.
The most common triggers are pathogens (like the common cold and flu viruses), allergens (like pollen or cat dander), and irritants, which can be chemical (like perfume) or physical (like dust), Dr. Voigt says.
In some cases, as with allergens and viruses, the trigger is not just the matter itself but the nose’s inflammatory response to it, Dr. Benninger says. Both allergic and nonallergic rhinitis (inflammation of the mucosal lining of the nose) can result in membrane swelling and excess mucus, potentially triggering sneezing. In the case of allergies, chemicals like histamine, which your immune system produces in response to an allergen, can also induce sneezing.
Here’s how the actual sneezing process goes down.
First, a foreign particle stimulates the trigeminal nerve, the largest nerve connecting to the brain. This sensory nerve provides feeling to numerous areas on the face and head, including the mucosal lining of the nose, mouth, and sinus cavities, as well as the skin, teeth, and back of the tongue.
Once stimulated, the trigeminal nerve relays a message to the brain, which then sends out various action signals to the body, Dr. Voigt explains. If your brain receives the message that an intruder is in your nose, your diaphragm tightens and moves down so your lungs can fill with air, your throat muscles relax, your mouth opens, your eyes close, and you sneeze. “The whole point is to generate pressure from our lungs to blow out what’s in our nose,” Dr. Voigt explains.
It’s also possible that there’s more going on here than science has yet unveiled. Although the trigeminal nerve is probably the predominant mechanism involved in most sneezes, Dr. Benninger says that there are likely other mechanisms at play that we don’t entirely understand, such as the involvement of other cranial nerves.
People can also sneeze in reaction to non-nose triggers.
One of the more well-studied examples is exposure to bright lights, a phenomenon called photic sneezing. Then, of course, there’s the wild occurrence of sneezing when you apply mascara or pluck your eyebrows. People have also been reported to sneeze during or after an orgasm. Sneezing can even result from strong emotions in some people, according to the U.S. National Library of Medicine.
The mechanisms in these cases are less well understood, Dr. Voigt says. It’s believed that, in general, this has to do with aberrations in people’s neural pathways—crossed wires in the brain, essentially.
Photic sneezing, for instance, is theorized to possibly result from some kind of cross-communication between the trigeminal and optic nerves. The thinking is that the message for the pupillary reflex, which shrinks the pupils when exposed to bright light, somehow crosses with the sneeze reflex, Dr. Benninger says. As SELF previously reported, actions like applying mascara or plucking your eyebrows trigger the ophthalmic branch of the trigeminal nerve, which might also prompt a sneeze depending on how your body interprets that messaging.
If you feel the urge to sneeze, you should. But cover it up.
Holding in a sneeze is not a good idea, Dr. Voigt says. This reflex can generate so much force that you could cause internal discomfort and even damage, including ear or sinus pressure or pain. And, while it’s very rare, people have been known to rupture their throats while holding back a sneeze.
It’s just as important to keep your sneeze to yourself, though. When you have an infectious disease like the cold or flu, sneezing can spray a fine, pathogen-containing mist all over the place, potentially infecting the people around you. “That’s how the virus travels into other people’s eyes, noses, and mouths,” Dr. Voigt says. Scientists believe these particles can travel six feet through the air—or more.
That’s why it’s best to sneeze either into a tissue or the crook of your arm, according to the CDC. “Just not your hand,” Dr. Voigt says. Your hand isn’t great at containing the spray. You’ll also have to sanitize or wash your hands immediately to prevent spreading germs, and that’s not always possible.
Even if your sneeze is due to something like an allergy or irritant exposure, it’s still gross to spritz your neighbors with mucus. Please be polite and spare them from that fate.