We all sneeze. Big, little, juicy, funny…we all do it. Medical pros call it sternutation: the sudden, semi-autonomous, convulsive expulsion of air from the lungs through the mouth (mostly) and nose. 

What’s a sneeze for? It can be a sign of a cold…a seasonal annoyance…even an embarrassment. But it’s also a healthy part of your body’s immune defense system. 

How Your Body Generates a Sneeze 

A sneeze starts with a signal to your nerves: “Something’s in your nose, get it out!” 

Something—an infection, an allergen, a physical irritant like smoke, dust, perfume, even cold air—stimulates the tiny hairs that line the nasal cavity. Specialized cells release histamines, which stimulate the nasal nerve endings (and create that itchy sensation).

The signal travels through the trigeminal nerve network to the brain, where it’s received in the “sneeze center” (the medulla oblongata, in the lower brain stem). An irresistible reflex response is born.

The reflex activates the pharyngeal and tracheal muscles in your head and neck, closing the esophagus and preparing the airway. Air pressure builds in your lungs. Your throat and eyes shut tight. Suddenly your throat and nasal cavities open up, fluid expresses from vessels in your nose, and a powerful burst of air and bioparticles rushes from your mouth (mostly) and nose at 100 miles per hour. Achoo!

Why Sneeze? 

The tremendous release of air in a sneeze jettisons mucus from your nasal cavity, cleansing the entire nasal cavity and clearing the original offending particles from your nose. (Add a handy tissue or handkerchief, and you’re good to go.)

Sneezing is an important part of your body’s immune defenses. It’s how your body expels foreign particles and excess fluids. A 2012 University of Pennsylvania study concluded that sneezing is a “natural reset” of the entire nasal environment—which unfortunately appears not to work in people with chronic nasal issues like sinusitis. 

A sneeze can also spread viruses and bacteria in each droplet of mucus and saliva. (That’s why it’s important to cover your nose and mouth, either with a tissue or by sneezing into the crook of your arm, and then wash your hands as soon as you can.)

A recent MIT study demonstrated that a sneeze—a “freely evolving turbulent puff cloud” of droplets and vapor—can travel up to 200% farther than previously thought. While large drops will land within 3 to 6 feet of the sneezer, small droplets can carry as far as 26 feet, even into ventilation systems. Those droplets can carry bacteria and viruses, too; new research from the University of Bristol, UK, found that any sneeze (or cough) can carry 100,000 germs into the air.

Other things can cause sneezing, too: 

• Sudden bright light or sunlight (18%-35% of people have this photic sneeze reflex)
• Plucking eyebrows, which stimulates the facial nerves in the same way as a particle in the nose
• Hard exercise, when rapid breathing dries the airway and the nose secretes fluid to keep membranes moist

• Eating too much—called snatiation, it results from a rare genetic condition 

Did you know that you can’t sneeze when you’re sleeping? The state of REM atonia keeps your motor neurons from being stimulated and reflex signals from being relayed to the brain; it keeps your body from acting out your dreams…or your sneezes. 

The Best Sneeze Defense 

The critical time for guarding against another person’s sneeze is the first few minutes after, as airborne droplets to fall to the ground. Here are some other commonsense tips: 

• Try to stay away from sneezers and coughers, if you can—if you’re sick, consider staying home so you don’t expose others.
• Keep a tissue or handkerchief handy to filter nearby sneezes and cover your own.
• Wash your hands frequently with soap and water, especially during winter.
• Carry alcohol-based hand sanitizer—a 15-second rub with a 62%-70% alcohol solution can help keep your hands germ free.

Resources

The sneeze reflex is a surprisingly important part of your immune system. Learn more about it from the references we consulted for this article. 

Cathy Cassata, “Here’s How Fast and Far a Sneeze Can Carry Contagious Germs,” Healthline.com, 2/1/19. Accessed 2/8/19.

Gillian Mohney, “Achoo! See the Anatomy of a Sneeze,” ABCNews.go.com, 8/24/16. Accessed 2/8/19.

Kimberly Holland, reviewed by Alana Biggers MD, “Why Do We Sneeze?” Healthline.com, 11/2/17. Accessed 2/8/19.

Lydia Bourouiba, “A Sneeze,” Images in Clinical Medicine, New England Journal of Medicine2016(375), 8/25/16. Accessed 2/8/19.

Mara Otero Fernandez, et al., “Assessing the Airborne Survival of Bacteria in Populations of Aerosol Droplets with a Novel Technology,” Journal of the Royal Society Interface16(150), 1/2/19. Accessed 2/8/19.

Pamela Georgeson, “Why Do We Sneeze?” ScientificAmerican.com, undated. Accessed 2/8/19.

WebMD Archives, “11 Surprising Sneezing Facts,” WebMD.com, undated. Accessed 2/8/19.

Wikipedia, “Sneeze,” Wikipedia.com, 2/5/19. Accessed 2/8/19.