Sneezes have taken on many meanings throughout human history. Early Christians considered them divine signs or devilish tricks, while the ancient Greeks interpreted them as omens, both good and bad.

But modern science has replaced all those superstitions with a physiological explanation: Sneezing is an integral part of the immune system, responsible for kicking out any material that tries to enter the body via the nasal passage. It’s essentially a defense mechanism, guarding against germs and irritants that could cause us harm.

“Just like skin is protective for us, part of the nose’s job is to be protective for us,” says Cecelia Damask, an Ear, Nose, and Throat (ENT) at Orlando ENT and Allergy.

What Happens When we Sneeze?

Unwelcome objects — like pollen, pet dander, dust motes, and viral particles — enter our sinuses all the time. Sneezing, also known as sternutation, is the body’s way of removing them.

As those invaders land inside the nose, they brush across the mucous membrane. The membrane releases chemicals that activate the trigeminal nerve (a large nerve responsible for sensation in the face), which then sends an electric signal to a part of the brainstem called the medulla oblongata. The brain, in turn, sets in motion a physical reflex to address the potential threat.

Almost instantly, the eyes close and the tongue shoots to the roof of the mouth. The diaphragm contracts, as do muscles in the chest and abdomen, and the vocal cords close to build pressure in the lungs. Then they reopen, propelling a powerful burst of air upward toward the mouth and nose — achoo!

“All of this happens within seconds,” Damask says. “That will expel any foreign substance.”

Those substances (along with a healthy dose of mucus) can travel as far as 27 feet, at a rate of 100 feet per second.

Read More: 4 Crazy Facts to Know About Your Nose

Why do we Sneeze More Than Once?

You’d think that one such explosion would be enough. But as we all know, it sometimes takes two or three (or a million) sneezes to fully evict the offending matter. The reason for this is unclear, but, as Damask half-jokingly put it, “some people may be more efficient sneezers than others.”

Interestingly, people’s sneezes differ in other ways besides efficiency. No two are quite alike — each one is the product of a unique lung capacity, as well as throat, nose, and mouth shape. Your sneeze, just like your voice, is yours and yours alone.

Read More: 6 Respiratory Illnesses That Could Mean Trouble for Your Lungs

Unusual Reasons for Sneezing

Though the original purpose of sneezing is to rid the body of contaminants, it also has more bizarre triggers. Due to some unexplained (but likely genetic) crossing of physiological wires, 20 to 35 percent of the population sneezes when looking at the sun, a phenomenon known as photic sneezing. For other people it happens after a big meal, a strange mix of sneeze and satiation dubbed snatiation. A few even feel compelled to clear their sinuses after orgasm, or when simply thinking about sex.

The sneeze still retains some of its mystery. But Damask notes that the provocative old wives’ tale isn’t true: Your heart does not stop when you sneeze. And, she adds, “it’s not a sign of some ominous hidden cancer or something awful like that.”

Sneezing won’t kill you, but for some people it can make life unpleasant. Allergies — and the incessant stuffiness that goes along with them — are the result of an overreaction by the immune system to substances that are usually harmless, like pollen.

Fortunately, antihistamines (or, in the most stubborn cases, a course of allergy shots) can be used to treat severe allergies. Though a single sneeze may feel good, it’s no fun living with them full-time.

Read More: Everything to Know About Allergies

Article Sources

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Cody Cottier is a contributing writer at Discover who loves exploring big questions about the universe and our home planet, the nature of consciousness, the ethical implications of science and more. He holds a bachelor’s degree in journalism and media production from Washington State University.