A sneeze often starts when an irritant enters the nose, whether it's mucus, dust or an allergen, and this stimulates the trigeminal nerve. An area of the brain called the "sneezing center" senses this and triggers a reflex reaction throughout the body. You take a deep breath in from the lungs, your muscles contract, your eyes close and there's a forceful outflow of air from the nostrils and mouth -- it's all intended to expel whatever was irritating your nose.
"Sneezing is a defense mechanism to protect against a foreign body entering," Holbrook said.
Sneezing is also a subject of curiosity among ear, nose and throat physicians, as well as sinus specialists who get their fair share of questions and hear many old wives' tales about it.
For example, Holbrook says he's been asked whether sneezing with your eyes open will cause them to pop out of your head (he reassures his patients that he has never heard of this happening).
Another myth is that your heart temporarily stops while sneezing.
And then there's the photic sneeze reflex, which is one example that has a medical basis. Looking at bright light or going from dark to light (indoors to outdoors) triggers a sneeze in some people.
About 25 percent of the population has this reflex, and it appears to be hereditary.
Another response that might seem strange and also has a tendency to run in families is sneezing when you have a full stomach. O'Brien says that both her grandfather and father sneeze when they first take a few bites of chocolate, although neither man is allergic to it. Fortunately for O'Brien, she did not inherit this reaction.
Sneezes are thought to travel at a speed of 100 miles an hour with a wet spray that may spread about five feet. So for those times when you need to say "achoo," there are some things to remember to do it safely.
Many experts agree that it was best to sneeze into the bend of your elbow, not into your hand. While you may have been taught as a child to cover your mouth with your hand when you sneeze to avoid spreading germs, kids and adults alike are now being taught to sneeze (or cough) into the inside of the elbow.
Sneezing into your hand is believed to be worse at spreading infection because the hand doesn't absorb mucus very well and often goes on to touch things afterward (instead of being immediately washed).
O'Brien also recommended keeping your mouth open because the sneeze is generating so much pressure you want to let it out.
As for what not to do, it could be risky to suppress a sneeze by pinching your nostrils or closing off your mouth. This can rupture an ear drum or damage the middle ear.
If you're going to sneeze, let it come, suggested Benninger. Historically, he explained, the Greeks believed that sneezing was a gift from the gods -- a signal from above, so to speak. This might be one reason why the phrase "Bless you" came into being, which probably was a derivative of "You are blessed."
As Benninger put it, "If people sneeze, just let them know they're blessed. The gods are with them."
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