The tickle at the back of your nose lets you know that within seconds you’ll be sneezing. A sneeze is also called a sternutation. This explosive release of fluid and air from your lungs, mouth and nose is involuntary and many times your body’s response to irritants in your nasal cavity.

During a sneeze your soft palate comes down and the back of your tongue rises to close off your mouth, routing most of the air from your lungs through your nose. But, since you can only partially close of your mouth with the soft palate and tongue, a considerable amount of air and fluid will also exit through your mouth.

Scientists do not believe that you can sneeze during your sleep as your body experiences a nearly complete inhibition of motor neurons, and thus movement during rapid eye movement (REM) sleep.1 This lack of movement is called REM atonia. A complete REM cycle takes approximately 100 minutes,2 but you may awaken long enough to sneeze during an REM cycle or between them.

The volume of your sneeze may change over time. In some, the sneeze is loud and voluminous while others give a small toot. However loud or large, your body uses a sneeze to rid your nose of an irritant, germ or mucous and to clear the passage for better airflow.3 Pet dander, dust, pollen and germs are all common reasons to sneeze, but your body responds with a sneeze to other triggers as well.

Why Do You Sneeze?

If you suffer from seasonal allergies, you’ll likely have experienced the irritating and burning sensation in your nose that immediately precedes a sneeze. Those protein-based allergens are irritating and frustrating. Sneezing protects your body by clearing your nasal cavity of viruses and bacteria.4 Scientists know that more than allergens and germs trigger this sensation. 

Dr. Neil Kao, allergy and asthma specialist from Greenville, South Carolina, explains that sneezing starts in your nervous system when signals passing along your nerves may take different paths to and from the brain.5 This can result in different ways in which people experience sneezing. For instance, you may have experienced a sneeze when plucking your eyebrows that triggered a nerve supplying your nasal passages, and thus you sneeze.

Exercise and sex are two surprising triggers for sneezing. Kao believes that during hyperventilation the mucous membranes in your mouth and nose begin to dry up. In response, your nose may begin to drip and trigger a sneeze.6 Sex stimulates the parasympathetic nervous system that may trigger signals during orgasm, resulting in sneezing.

It is not uncommon to sneeze more than once, or several times in succession. Dr. Marjorie Slankard, director of the allergy clinic at Columbia-New York Presbyterian Medical Center, believes the reason you may sneeze multiple times is related to the reason you started sneezing in the first place.7 In other words, sometimes it takes two, three or even four sneezes to rid your nasal cavity of what irritates it.

Researchers have found evidence that sneezing may be a natural way your nose and brain “reboot” in much the same way your computer reboots after Microsoft Windows’ infamous blue screen of death.8 Biochemical signals regulate the beating of microscopic ciliary hairs that line your nasal cavity triggering a sneeze and literally resetting the environment within your nasal cavity to near normal conditions.9

Data suggests that those who suffer chronic sinusitis may have limited ability to clear their nasal cavity despite the outward appearance of a “normal” sneeze. Researcher Dr. Noam Cohen, from the department of otorhinolaryngology head and neck surgery at the University of Pennsylvania, was involved in the study and commented on how a better understanding of effective sneezing may improve quality of life, saying:10

“While sinusitis rarely leads to death, it has a tremendous impact on quality of life, with the majority of symptoms coming from poor clearance of mucus. By understanding the process by which patients with sinusitis do not clear mucus from their nose and sinuses, we can try to develop new strategies to compensate for their poor mucus clearance and improve their quality of life.”

Superstitions Are Something to Sneeze Over

There are many superstitions surrounding sneezing that have developed over years and many cultures. For instance, it is not true that your heart stops during a sneeze.11 Instead, your chest contracts and your blood flow may be constricted, changing the rhythm of your heartbeat, but the heart definitely doesn’t stop.

During a sneeze your eyes involuntarily close, giving rise to the superstition that your eyes will pop out of your head if your lids are not closed tightly during a sneeze.12 Despite the discomfort closing your eyes may elicit while driving, there is nothing you can do to keep your eyes open while sneezing, much like the involuntary reflex you have when the doctor taps the tendon under your knee cap. 

Kao points out that while blood pressure in the eye may increase slightly during a sneeze, it is not nearly enough to cause the orb to pop out of your head.13 Other myths about sneezing include if your cat sneezes it’s going to rain, or when you sneeze either people are coming to visit your home or someone is thinking about you.14 Decades ago British nurses believed that babies were under a fairy spell until their first sneeze, and in Tonga, when a child sneezes it means bad fortune for the family.