Why do your eyes slam shut every time you sneeze? It's not to save your eyeballs

It happens quicker than thought. A tickle climbs the back of your nose, your breath snatches inward, your face crumples, and in the half-second before the aaa-CHOO, your eyes clamp shut entirely on their own. You might be mid-sentence, mid-road, mid-anything. It makes no difference. For one brief, blind moment, the world goes dark, and then it is over, your eyes flick open, and you carry on as though nothing strange has happened at all.But something strange has. You have just been briefly blinded by your own body, dozens of times a year, without ever once agreeing to it. So why do our eyes insist on closing every single time we sneeze?WHY DO WE CLOSE OUR EYES WHEN WE SNEEZE? Because you are not the one giving the order. Shutting your eyes during a sneeze is a reflex, an automatic action your body carries out without waiting for your permission, in the same family as your leg kicking out when a doctor taps your knee.To see why, follow a sneeze from its beginning. A sneeze, known to doctors by the splendid name sternutation, is your nose's way of blasting out something that should not be there: a fleck of dust, a grain of pollen, a lungful of pepper, or a cold virus. When the delicate lining of your nose is irritated, it fires a warning along the trigeminal nerve, the main nerve that carries sensation from your face and nose, up to a small cluster of cells low in the brain, in the region called the brainstem, that acts as the sneeze's command centre. A sneeze travels from the nose along the facial nerves to the brain, which fires the eyelids shut too. (Photo: Getty) From there, the order goes out, and it is not a single tidy instruction. It is a whole coordinated storm. You draw a deep breath, your chest and belly muscles brace, the back of your throat closes, pressure builds, and then everything releases in one violent rush of air. Swept up in that same burst of signals, almost as an afterthought, are the small muscles that ring your eyes and pull the lids down. The sneeze command simply spills over onto them. Your eyes close, in other words, because they happen to be wired into the same circuit that is busy firing everything else.WILL YOUR EYES REALLY POP OUT IF YOU SNEEZE WITH THEM OPEN? Almost certainly you were told, as a child, the delicious warning: keep your eyes open when you sneeze, and they will shoot clean out of your head. It is a wonderful story. It is also completely untrue. Each of your eyes is held firmly in its socket by six muscles, and the socket has no open passage connecting it to your nose, so the force of a sneeze has no route by which to push an eyeball out from behind. The pressure that does build during a sneeze gathers in your airways, and a little in your blood vessels, not behind your eyes. Shutting the eyes may shield them from the spray of germs and irritants a sneeze flings out. (Photo: Getty) Doctors are clear that a sneeze cannot launch your eyes from their sockets, whether they are open or shut. You can, with enough effort, sneeze with your eyes wide open, and the only thing that pops is the myth. The tale seems to have grown from a single 19th-century anecdote about a burst eyeball, hardened over generations of schoolyards into a supposed law of nature.SO WHY DID OUR EYES LEARN TO SHUT AT ALL? Here the science turns satisfyingly uncertain. If the eyelids are not holding your eyeballs in, what exactly are they doing?The most popular answer is protection. A sneeze is a dirty business, flinging a fine spray of mucus, irritants and germs out of the nose and mouth at considerable speed, and drawing the lids shut may be the body's way of closing the curtains before the mess flies, keeping that cloud of expelled particles from landing straight back in your eyes.Not everyone is convinced it is so purposeful. Because it is possible, with effort, to sneeze with the eyes open. Some doctors argue the closing is not strictly necessary and may be little more than an accidental side effect of so many neighbouring muscles firing at once, a reflex that rides along for free. What is certain is that it is deeply built in, not a habit we pick up. Even newborn babies scrunch their eyes shut when they sneeze, long before they could have learnt it by watching anyone at all.WHY DO SOME PEOPLE SNEEZE WHEN THEY STEP INTO SUNLIGHT?If you want proof of how easily the body's wires cross, consider this. Roughly a quarter of all people sneeze when they walk from shade into bright sunshine, a quirk scientists have given the gleeful name the ACHOO syndrome, short for Autosomal Dominant Compelling Helio-Ophthalmic Outburst. It runs in families, handed down from parent to child.The likeliest explanation is a crossed signal. The sudden flood of light sets off the nerve that shrinks your pupils, and because that nerve runs so close to the trigeminal nerve, the one that sparks a sneeze, the message appears to spill from one into the other, and the brain, briefly muddled, calls up a sneeze. It is the same principle as eye-closing itself, one reflex bleeding into another, the nervous system's signals brushing shoulders in a crowded corridor.So, the next time a sneeze seizes you and the world blinks out for half a second, do not fight it. There is no danger in it, and there is no need to prise your eyes open against the tide. It is only your body doing what it has always done, firing off an ancient, tangled reflex so fast and so completely that it sweeps your eyes shut along with it, and hands them back a heartbeat later, blinking, as if to ask where you were.- Ends