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What happens in your body when you sneeze?

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📓 The short answer

A sneeze begins when irritants in your nose trigger immune cells to release histamine, which stimulates nerve endings that send a signal to the brainstem’s “sneeze center.” In response, you take a deep breath, tense your chest and abdominal muscles with your vocal cords closed, then forcefully expel air through your nose and clear out the irritants.

📚 The long answer

Your body has an arsenal of tools to protect you from foreign invaders. One of the most powerful is the sneeze.

A sneeze is an involuntary reflex that removes irritants from your nose and throat using a forceful burst of air. If you just sneezed, bless you (and check out the bonus question for why we even say that)!

Here's what goes on inside your body when you sneeze.

Step #1: Irritants trigger immune cells to release chemicals

A sneeze starts when immune cells in your nose and throat detect an irritating foreign substance. Common triggers include pollen, dirt, dust, mold, pepper, smoke, and excessive mucus. For some people, bright light and even stress or strong emotions can trigger sneezing.

The nasal and throat lining contains immune cells called mast cells and eosinophils.

Left: "Mast cell" by Dr. Roshan Nasimudeen is licensed under CC BY-SA 3.0. Right: "Eosinophil 2" by Dr Graham Beards is licensed under CC BY-SA 3.0.

When these cells notice an irritant, they release histamine, a chemical that signals a foreign material has been identified.

Step #2: Histamines irritate nerve endings in the nose

At this point, you may feel a little tickle and snot in your nose. Histamines have begun to irritate nerve endings (causing the tickle feeling) and triggering tiny blood vessels (causing the leaking fluid). Crucially, the nerves are getting the message that a foreign substance has entered the nose.

Step #3: Irritated nerves send a signal to your brainstem

The irritated nerve endings send a message to your brain that something's off. These signals travel along the trigeminal nerve to a region of your brainstem called the "sneeze center."

Left: "Trigeminal Nerve"​ by ​BruceBlaus​ is licensed under ​CC BY-SA 4.0​. Right: "Medulla oblongata and foramen magnum animation small" by Anatomography is licensed under CC BY-SA 2.1 JP.

Once the "sneeze center" gets enough of these "there's a foreign invader in the nose" signals, it triggers the reflex that commands all muscles involved in the sneeze.

Step #4: Sneeze reflex triggers a sudden inhalation and pressure buildup

A sneeze is most effective when a large volume of air is expelled forcefully. First, the reflex causes a sudden, deep breath. Then pressure builds to achieve a high velocity of airflow.

Your glottis (a term to describe your vocal cords and the muscles around them) closes so that air can't escape from your lungs. Your chest and abdominal muscles also tense to increase the pressure, and your eyes squeeze shut.

Step #5: A forceful exhalation clears irritants from the nose

When pressure peaks, your brain signals the vocal cords to part, allowing all the high-pressure air built up in your lungs to rapidly travel up through your windpipe, throat, and out through your nose (and mouth, to a degree).

Part of the mouth even adjusts automatically so most air exits through your nose. Specifically, the soft palate and uvula in the back of your mouth tilt and your tongue presses against the roof of your mouth.

The forceful release of air through your nose lasts about 0.15 seconds and can reach speeds up to 100 mph (160 km/h). If the sneeze doesn't clear out the irritants, you may need to sneeze a couple more times.

Step #6: Post-sneeze effects

After the sneeze, there's still a lot going on in your body.

Tense muscles relax, and breathing returns to normal. You may still feel sniffly because the histamines that caused blood vessels to leak fluid may still be hanging around.

Your nose is also still working to make sure the nasal lining is in tip top shape. A 2012 study found that your cilia — microscopic, shag-carpet-like structures in your nasal lining that continuously push mucus to the out of your airways — become hyperactive after a sneeze. For a few minutes, your cilia work extra hard to clear out any extra mucus or lingering irritants, giving your nose its best chance of returning to a non-irritated state.

The researchers theorize that people who suffer from chronic rhinosinusitis (long-lasting nasal inflammation) may have underperforming cilia. As a result, excess mucus and irritants stick around, leading to inflammation symptoms like a runny nose and sneezing.

Finally, you may notice that you feel good after a sneeze. That's thanks to the release of endorphins post-sneeze. These sneeze-triggered endorphins help reduce stress, relieve pain, and generally just make you feel good. Call it an achoo-ahhhhh 😌.

🧠 Bonus brain points

Why do we say "bless you" when someone sneezes?

No one knows for sure, but there are a few theories why English speakers say "bless you" after someone sneezes (other languages also offer similar blessings and wishes of good health):

Theory #1: Protect the sneezer from death

Some believe that the refrain came from Pope Gregory I in 6th century Rome when the bubonic plague was raging in Europe. The idea was that blessing the sneezer with this mini prayer could help them avoid death, since sneezing was a symptom of the plague.

Theory #2: Protect the sneezer from losing their soul

It's also possible that "bless you" was said out of superstition. Some thought that the soul resided in the head, and since air came out through the nose, a sneeze might accidentally be releasing the soul.

Theory #3: Protect the sneezer and those around them from evil spirits

A sneeze has also thought to be a form of evil spirits leaving the body. So a quick "bless you" could help the sneezer (and those around them) from these evil entities.

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

🌐 Wikipedia article of the week

​Dancing plague of 1518​

"The dancing plague of 1518 ... was a case of dancing mania that occurred in Strasbourg, Alsace (modern-day France), in the Holy Roman Empire from July 1518 to September 1518. Somewhere between 50 and 400 people took to dancing for weeks. There are many theories behind the phenomenon, the most popular being stress-induced mass hysteria.... Other theories include ergot poisoning. There is controversy concerning the number of deaths."

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👀 Catch up on other curious questions

• ​Why does bright light cause some people to sneeze?​​
• ​Why do we say "brand" new?​​
• ​How are cosmetic expiration dates determined?​​

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