Why do people sneeze?

God bless you! Gesundheit! Cover your face!

When you sneeze, you are likely to hear one of these responses, ranging in inspiration from the medieval to the hygienic. Different cultures throughout history have interpreted a sneeze as either an auspicious sign or a bad omen, but it may be said that both are right: Sneezing is the good that gets the ill out.

“Sneezing is basically ‘nature’s broom,’” says Dr. James Banks, an allergist and immunologist in private practice in Arnold, Md. “It is a way our bodies purge foreign matter that has invaded our noses.”

Particulates are the usual suspects, including dust and common allergens like pollen or animal dander. Sneezing also expels unwelcome germs when we are sick, which has given rise to the sanitary concerns about honking away in public places. And for good reason: a single sneeze can produce some 40,000 aerosolized droplets containing a hefty amount of infectious organisms, according to a 1998 article in the American Journal of Infection Control.

It’s not just allergies and illnesses that can produce that familiar tickling in the nose. Banks explains: “People sneeze for a lot of reasons other than just getting something up their noses. Clinically speaking, we consider sneezing a non-specific reaction, because there are a lot of sources that irritate.”

For example, some people experience a round of sneezing after a large meal, which has led to the coining of the term snatiation, a combination of sneeze and satiation. There is also a phenomenon with a known genetic basis called the photic sneeze reflex, which causes about one-third of people to sneeze from looking at a bright light source, such as the sun. Sigmund Freud has even speculated on the kinky psychological origins of an otherwise innocuous sneeze.

“Overall, it is not a clear-cut reflex,” says Dr. David Kaufman, an associate professor in the department of otolaryngology at New York University Medical Center (an otolaryngologist is most often referred to as an ear, nose and throat specialist).

Like blinking or breathing, sneezing is a semi-autonomous reflex, meaning we exercise some conscious control over its mechanism – we can try to restrain ourselves or submit and start reaching for a tissue.

The act of sneezing itself, technically called sternutation, usually begins as an electrical signal that is triggered by a trespassing particle’s contact with nerve endings in the mucous membranes of our sinuses. This neural message then travels to the brain stem, which is located in the lower rear of our head where the spine connects to the brain and controls rudimentary bodily functions such as respiration and swallowing.

Once the command for a sneeze has reached the brain stem, an “all points bulletin” is sent throughout the body’s musculature and a powerful, coordinated contraction takes place. Our eyes are forced closed, and other facial, chest and abdominal muscle groups are recruited as well. Some muscles actually anchor and brace us while in the throes of a nasal outburst to avoid unintended bodily injury.

“They keep us from jet-action, throwing ourselves across the room,” says Banks.

A typical sneeze has a velocity of about 100 miles per hour (160 kilometers per hour), an impressive hurricane squall, while a regular breath idles along at just 5 mph. That 20-fold increase usually serves to eject whatever it is that is causing the offense, but some people have to blast out several sneezes, oftentimes hilariously, before finally getting a well-deserved break.

Scientists have yet to come up with a good explanation for why most people sneeze the predictable two or three times, while others are wracked by staccato attacks. But the answer seems to lie in an individual’s unique immunological and neurological constitution.

“Multiple sneezes are more common in allergenic individuals, especially those with an ongoing chronic stimulus of some sort,” says Banks.

What if you hold in a sneeze? There is the often-repeated fear that an internal backfiring can burst capillaries in the sinuses or eyes, injure the delicate inner ears or even cause a stroke.

Dr. Clark Kaufman, a pediatric allergist in private practice in Lancaster, Pa., thinks this is unlikely. “It’s not dangerous,” he says. “Most people do it all the time and get away with it.” But he cautions that as your body may be trying to dislodge something, it’s probably not a good idea to hold back on a routine basis.

So chances are you won’t do any permanent damage if you quash that sneeze during a job interview or a date. To help suppress the urge, try placing your index finger under your nose.

“This sends sense signals to your brain using the same neural pathways that a sneeze does,” advises Banks. By doing this, you can “overload your neural circuitry” and prevent the sneeze from occurring.

In lieu of putting a finger to the face in a gesture that unintentionally mimics a mustache, Banks also recommends breathing through one’s mouth, as this will decrease turbulence in the nose and may help thwart the impending “atchoo.”

On the other hand, if you have a sneeze that refuses to come out or go away, and you’re grimacing awkwardly in public, close your mouth and inhale through your nose to further excite the nerve endings. This will assist in getting you across the threshold so the sneeze reflex kicks in, and then you can just let ‘er rip.

After all, if Freud is to believed, sneezing is actually sort of sexy – though don’t expect to hear “hubba hubba” the next time you do.