Sneezing or sternutation, that quick blast of air out our noses and mouths, has numerous causes. Often we know why we’re sneezing. We may have runny noses from colds or flus, which cause the mucous membranes in our sinus passages to become irritated. They respond by attempting to clear these passages by causing us to sneeze.

At other times, allergies to pollens, dust, or molds create sneezing. The nose, which is acting as a filtration device, works to remove these allergens by expelling them in a sneeze. Since allergies entering the nose are often made up of tiny particles, it may take multiple sneezes to do the trick of removing irritants. Furthermore, provided we remain in an environment with the offending allergens, we’re likely to keep sneezing periodically.

Sometimes cures for sneezing from allergies bring on larger sneezes. Using corticosteroid nasal sprays like Flonase® for instance, can bring on a bout of sneezing. Again the nose reacts at the introduction of a foreign agent, even if it is beneficial, and attempts to get rid of it. The nasal passages will also note the presence of irritating foreign agents that get in the nose, like pepper and certain other spices. Or you may sneeze after swimming for a while.

One unusual cause of sneezing is drug withdrawal from opiates. Opiates make up many different legal pain relievers, and several illegal drugs like heroin. If you have been taking opiates for a long period of time, you can have withdrawal symptoms once you stop taking them. These can include runny nose and sneezing that may be caused by nasal congestion. Some people appear to suffer from chronic runny nose, creating greater likelihood they will sneeze frequently. This suggests that the presence of extra mucus in the sinuses is more likely to provoke the sneeze reaction.

There is one type of sneeze that has little to do with nasal irritants. The photic sneeze is an inherited reflex that affects about 20-35% of humans. What occurs during a photic sneeze is that looking at bright light stimulates the optic nerve to send a wrong signal to the trigeminal nerve, which is thought to be the nerve responsible for sending a signal to create a sneeze. Some scientists consider photic sternutation as a congenital defect, but given the high number of people who sneeze when looking at light, it may simply be a natural variant.

Scientists do know that the photic sneeze is autosomal dominant in nature. If your parents sneeze when they get sudden exposure to sunlight, chances are you will too, and you have a good chance of passing this trait onto your children. Fortunately, a sneeze is seldom dangerous unless you are pursuing an activity that requires constant vigilance. If you do find yourself having several sneezes in succession while driving, for instance, you might want to pull to the side of the road until the sneezes have ended.