When something tickles your nose, the natural reaction is to sneeze. It seems like a simple thing, but you might be surprised at what can cause some people to sneeze.
Anatomy of a Sneeze
During normal breathing, air moves in and out of the lungs through the nose. The nose helps adjust the temperature of the air, adds humidity to the air, and filters out things that don’t belong inside the body, like allergens and dust particles. When something irritates the mucus membrane lining the nose, nerve endings send a message to the brain to signal itching or tickling.
When the brain gets the signal from the nose, it sends impulses to the nerves that control the muscles in the head and neck to close the vocal cords and allow air pressure to build up in the lungs. When the cords suddenly open, the air bursts out through the nose and mouth, pushing the irritants out with it in what we know as a sneeze. At the same time the sneeze takes place, you may also notice that your eyes close. While the old wives tale isn’t true that your eyes would pop out of your head when you sneeze if they didn’t close, it is true that the brain automatically signals the eyes to close at the split second the sneeze takes place.
Sneeze Triggers
A variety of things can trigger a sneeze. Most people react to dust, pollens, chemicals, and infections by sneezing. Some people have more unusual sneeze triggers, including when they feel chilled or when they pluck their eyebrows.
One of the most frequently recognized genetic traits that can be passed from a parent to a child is the photic sneeze reflex. People with this syndrome react to sudden exposure to bright light after being in a darker environment. Most often, the reflex is triggered when someone walks out of a darker building into bright sunlight. Some people with the condition sneeze rapidly 2 or 3 times, while others have been heard to sneeze up to 40 times in a row. Studies show that between 20 and 30 percent of people have the photic sneeze reflex.
Courteous Sneezing
Since people sneeze for a variety of reasons, you can’t always assume that someone who sneezes is necessarily sick. But any sneeze will spread thousands of droplets from the nose at a speed of approximately 100 mph (150 km per hour) over a range of several feet. In the case of someone with a cold or other illness, one sneeze can spread the infection over a wide area. So any time you feel like you are about to sneeze, remember to be polite to those around you and cover your nose and mouth.
Resources:
Scientific American: Why Do We Sneeze?
Scientific American: Photic Sneeze Reflex
Science In Action blog