The average healthy person sneezes four times a day.

In official doctor language, a sneeze is “a physiological response to the irritation of the respiratory epithelium lining of the nose.” The official name for sneezing is “sternutation,” from the Latin word meaning “to sneeze.”

Doctors compare a good hearty sneeze to a computer reboot. The force of it gives a tremendous shake to everything in the nasal passages, dislodging mucus and cleaning off the nasal hairs.

Sneezing is a cooperative effort between the throat, chest, diaphragm, and abdomen. It’s nearly impossible to sneeze with your eyes open, and it’s almost as difficult to refrain from leaning forward during a sneeze.

A sneeze can travel up to 100 mph (160 kph) launching 40,000 droplets that contain 100,000 germs into the air. Large droplets can travel up to 5 feet (1.5 m), but smaller droplets can go as far as 30 feet (9 m) , which is far enough to enter ventilation systems. Those germs can stay aloft for 45 minutes.

Compare that to a single cough, which can launch a mere 3,000 germy droplets.

Sneezing is triggered by many different things: pollen, dust, animal dander, pollutants, dust mites, mold spores, tobacco smoke, perfumes, and of course, viruses. A typical city dweller inhales an estimated 20 billion foreign particles every day.

About one-third of humans are able to trigger a sneeze by looking at a bright light, such as the Sun. This is called a photic sneeze reflex, from the Greek word for light. This does not mean that they constantly sneeze when they are out in the sunlight; it merely means that when they feel a sneeze coming on, they can force it out by glancing at the Sun.

Histamine is a chemical that sends signals through the body. Normally, histamine protects the body from invaders such as germs and parasites by sounding the alarm whenever an invader is present. These alarm chemicals cause the nasal passages to become engorged with mucus in order to flush the danger out. But sometimes histamine can respond to substances that are not actually dangerous, including allergens such as pollen. If someone is sneezing because of these false alarms sent out by histamine, an anti-allergen medication containing antihistamines will help calm the symptoms by suppressing the histamine response. However, if a person is sneezing because they have a cold, antihistamines won’t help at all.

Holding a sneeze in can damage the nasal passages and cause small blood vessels in the eyes and nose to rupture. There are safe methods to stifle a sneeze. Try pinching your upper lip beneath your nose, or pinching the top of your nose between the eyebrows. Some people tickle the roof of their mouth with their tongue, or press their tongue hard against the top front teeth. Others kill a sneeze by pronouncing some odd word just when they feel it coming on, such as “pumpernickel” or “pickle.”

Can you sneeze when you’re asleep? No, because when you are asleep, your nerves are also “asleep.” During REM sleep, all muscles are paralyzed. If someone doses you with sneezing powder while you’re sleeping, it will wake you up, and then you would sneeze. But if you’re snoozing, you’re not sneezing.

It’s impossible to sneeze properly without making noise. When air exits the body at 100 mph, the force of the explosion generates a sound. In the U.S., the name of that noise is “achoo.” In France they say “atchoum.” Italians say “hapsu,” Japanese say “hakashhon” and the Swedish say “atjo.”