What Causes Sneezing & Coughing?

Sneezing and coughing are similar reactions that serve the same basic purpose for two different parts of the respiratory system. They're designed to keep this system as clear as possible, and to deal decisively and violently with irritations and obstructions. Nevertheless, abnormal conditions, including various diseases and even a common genetic condition that results in a strange set of "crossed wires," can trigger the usually healthy and natural sneezing or coughing reflexes.

Irritants

• When either the throat or the nasal passages become irritated by the presence of an unwanted object--a misswallowed piece of food in the throat or a particle of dust in the nose--the body responds violently to expel that object. In sneezing, the irritation is sensed by the trigeminal nerve, which manages facial sensation and motor control. The nerve sends a signal to the brain to contract the facial muscles and propel air through the nose, expelling the particle at about 100 miles per hour. In coughing, it's the laryngeal nerve that sends the signal. Both coughs and sneezes propel air very quickly through the systems they're meant to clear, and are designed to continue until the offending object has been dislodged.

Disease

• There's actually not much difference between the function of a sneeze or cough caused by disease (like a cold) and a normal, "healthy" sneeze or cough. When you have a cold, your mucous membranes secrete much more mucus into your nasal passages, which your body then attempts to clear by sneezing. Also, certain substances will cause an abnormal level of mucus production in those who are allergic, which will also lead to sneezing for the same reason. Serious diseases like tuberculosis, pneumonia and pertussis cause severe inflammation and irritation of the throat, triggering the cough reflex.

Photic Sneeze Reflex

• About a third of the population also sneezes upon sudden exposure to bright light. According to Scientific American, most experts now attribute what's called the photic sneeze reflex to the close physical proximity of the optic nerve--responsible, among other things, for the contraction of the pupils in high-light conditions--to the trigeminal nerve. When the optic nerve fires the electrical signal to contract the pupils, the trigeminal nerve absorbs some of the electrical signal and orders a sneeze. The photic sneeze reflex appears to be genetic, and is autosomal dominant, meaning that about half of the children of a person with the condition will inherit it.