Sneezing happens when a strong blast of air is suddenly expelled from the nose and sometimes the mouth (if it remains open). The fancy medical term for sneezing is sternutation. It is a normal, natural in-born response just like scratching, coughing, and yawning. Sneezing is a semi-autonomous reflex. This means that the act of sneezing is somewhat involuntary (we have no or little control over it), instantaneous, and is a response to a stimulus in the environment.
Although some folks sneeze more often than others, sneezing is usually a common occurrence for most people. Even tiny babies sneeze. So do many types of animals. The function of a sneeze is to rid the body of foreign particles or irritants that may be trapped inside the nasal passageway. This happens when an irritant (such as pollen, dust, or pepper) tickles the nasal lining and sends a signal to the brain. The brain responds by coordinating a complicated reaction that involves the body’s eyelids closing, lungs filling up with air, abdomen tightening, and contracting of the diaphragm (the large muscle below the lungs that is necessary for breathing). It’s impossible to sneeze while you’re sleeping, or to sneeze with your eyes open.
There are a variety of factors and situations that can cause a person to sneeze. Some involve illness. Others involve the surrounding environment. Here are some of the most common causes:
Allergies. People who are allergic to dust, mold, mildew, pollen, perfumes, or pet dander (such as from a dog or cat) may experience irritation of the nasal passages which can result in sneezing. Hay fever is an allergy-related cause of sneezing that affects thousands of people worldwide.
Irritants. Excessive amounts of dust, smoke, chemicals, or particulates in the air can trigger sneezing as a protective mechanism in order to clear the nasal passageways and avoid airway obstruction.
Bright light. Some people sneeze after looking at the sun or at a bright light. Although the scientific term for this is the photic sneeze reflex, it is more commonly known as “sun sneezing.”
Cold air. Exposure to cold air can trigger the sneeze reflex.
Plucking eyebrows. When you pluck your eyebrow hairs you may inadvertently stimulate the Trigeminal nerve which has branches that extend to the eyebrows and also into the nose. This in turn can trigger a sneeze response. For this reason, you can sometimes avoid sneezing by immediately applying pressure to your eyebrow.
Illness. Respiratory infections can cause sneezing from inflammation of the nasal passages. The act of sneezing can project mucous and germs at speeds of up to 100 miles per hour, that can travel a distance of over 10 feet, spreading up to 40,000 tiny germ-filled droplets. For this reason, it is exceedingly polite and health-conscious to cover your sneeze by sneezing into the crook of your elbow. Those around you will be grateful.