Sneezes: Here’s Exactly What Happens When You Sneeze—and Why

Updated: Nov. 23, 2020

Why do people sneeze? We asked experts to tell us how and why we sneeze, common irritants, and how to avoid spreading germs.

Whether you’re a dainty, blowhorn, or keep-it-to-yourself sneezer, there’s one thing we all have in common⁠—just about everybody sneezes. From babies to the elderly, our bodies are programmed to produce these involuntary reactions when our nostrils detect an irritant. That’s the simple explanation of why we sneeze.

But what actually happens in our bodies that produces these blasts of air, sometimes with little to no warning? There are a lot of factors that come into play, so we asked the experts to break down the anatomy of a sneeze. Also, check out these 12 weird facts you never knew about sneezing.

The causes and triggers of sneezing

“Sneezing is one of our body’s most common reactions, but we don’t often take the time to stop and think about how and why it happens,” says Tim Mynes, DO, an emergency medicine physician at MedExpress Urgent Care, in Lynchburg, Virginia. “Sneezing is simply an involuntary release of air that helps the body to get rid of irritants in our nose and throat, like allergens, dirt, and dust.”

Our sneezing activity may see an uptick when we experience allergies or a cold, but Dr. Mynes points out that we can also experience a good old gesundheit for lesser-known reasons.

“These other triggers can range from dirt, debris, and even nasal sprays, to sudden exposure to bright light, nose trauma, or breathing cold air,” he explains. “We may sneeze when we breathe cold air because our nasal mucus dries up and can crack, which triggers the same response in the nerves in our nose as common irritants like dust.”

In a 2019 study published in Scientific Reports, researchers found that a type of sneezing that can be induced by bright light, also known as phoetic sneeze reflex, is an inherited, genetic trait. They looked at more than 3,400 people in China and found an association between the phoetic sneeze reflex and specific genes. This reflex, which is also called autosomal dominant compulsive helio-ophthalmic outbursts (ACHOO) syndrome, causes uncontrollable reflexive sneezing when there is exposure to bright light, and occurs in one out of every four people. (In the study, it was seen in 30% of men and 21% of women.)

The sneeze reflex

Our bodies are complex machines, so while sneezing just feels like something we do, our bodies are performing many steps to make that reaction happen.

“The sneeze reflex starts with the irritation of the nasal lining as sensed by the cilia on these cells,” says Dilraj Kalsi, MD, a lifestyle doctor specializing in functional medicine and founder of Hippocrates Lounge, a lifestyle clinic targeting chronic illness in London. (Cilia are hair-like structures found on the surface of cells that can detect irritants.) “These receptors send signals via sensory trigeminal nerves to the sneezing center in the lateral medulla of the spinal cord.”

Next up in the process is the triggering of two different nerve signals. Dr. Kalsi says one is dispatched via motor nerves to pharyngeal, laryngeal, and respiratory muscles causing us to sneeze. The other is transmitted via parasympathetic nerves increasing nasal and tear secretion. (Check out the really weird things that can make you sneeze.)

Before the sneeze

“Just before you sneeze, pressure builds up in your chest as your chest muscles compress your lungs, and your vocal cords close,” says Dr. Mynes. “When your vocal cords suddenly open again, air is driven up your respiratory tract and through your nose at a high speed. Your eyes shut and your diaphragm moves upward as your chest muscles contract, releasing air from your lungs.”

That air allows thousands of droplets to project from your nose and mouth as a way to get rid of the allergen or irritant. Dr. Mynes says that while sneezing helps get rid of unwanted particles from the body, it also can spread sickness through those thousands of particles.

Dr. Mynes always reminds patients to cover sneezes by sneezing into their upper arm, elbow, or into a tissue, rather than hands. (More on sneezing etiquette below.)

Different types of sneezes

As mentioned earlier, there are many different types of sneezes. We hear them everyday. Some people have grandiose sneezes, while others sneeze as quiet as a mouse. You may have a friend or colleague who even looks to suppress their sneezes, almost keeping them internal. (This is how bad it is to hold in a sneeze.)

“Many patients wonder why they may sometimes sneeze more than once⁠—or why their sneezes may be louder than others,” says Dr. Mynes. “This is often because your body responds differently to allergens depending on the type and amount.”

(Are sneezes, burps, and other bodily functions on your mind? These are 10 things you’ve always wanted to know.)

Other reasons for sneeze variations

Individuals can vary in their sensitivity to irritants and allergens. According to Kalsi, people can also respond to different stimuli altogether. Differences in the sounds of sneezes come from the variance in their nasal anatomy and respiratory muscle strength.

“If you sneeze multiple times in a row, it probably means that your body didn’t get rid of the irritant after the first sneeze and is still working to remove it,” says Dr. Mynes. “The volume of the sneeze typically depends on the amount of air you inhale before sneezing, as well as your lung capacity; the more air you take in, the more air that comes out, which can produce a bigger sneeze.” (If you feel like you can’t stop sneezing, this is probably why.)

Sneezing etiquette: How to sneeze properly

As the Centers for Disease Control and Prevention (CDC) points out, sneezing is one way that illness and diseases are spread. The CDC recommends covering your mouth and nose with a tissue when sneezing and then disposing of it immediately. Your next step is to wash your hands.

No tissue? Don’t panic. In that case, it’s better to cough or sneeze into your upper sleeve rather than your hands. Any way you handle a sneeze, make sure you wash your hands right after to avoid exposing others to germs.