I have allergies, and whenever they flare up, I sneeze a lot. Why do people sneeze?

Q: I have allergies, and whenever they flare up, I sneeze a lot. Why do people sneeze?

A: A sneeze is an audible, forceful burst of air from the lungs that exits through the nose and often the mouth, as well. Sneezing is an involuntary reflex by the body, although you can voluntarily fake a sneeze.

Sneezes are powerful. More than 40,000 particles can be expelled during a sneeze (yuck) - no wonder it may help spread illness. These particles shoot out very fast; estimates are that they travel 100 miles per hour or more. In fact, one source I found noted that a sneeze can blow out at three quarters the speed of sound: more than 600 miles per hour! That is nothing to sneeze at (I couldn't resist).

Most sneezes are caused by irritation of the nose. Particles get trapped by the hairs in the nose or just get stuck to the moist lining (mucosa) of the nose (filtering these particles is part of the function of the nose). These particles can cause histamine and/or other substances to be released. These, in turn, can stimulate nerves to send a signal to the brain which, in turn, stimulates signals via other nerves to activate muscles of the chest, abdomen, throat and mouth to violently expel air while at the same time causing the vocal cords to relax. The result is a sneeze.

The most common irritants that initiate this cascade of events are allergens (for those with allergies), infections (such as colds) or other irritants (for example, pepper). This would seem to imply that the sneeze reflex is intended to blow these irritants out of the nose and airway, and indeed this may be true (no one really knows for sure).

However, there are other causes of sneezes. About one in every three people has an inherited condition that may cause them to sneeze when they are suddenly exposed to bright light (usually sunlight). There is also an inherited predisposition in some people to sneeze when they have a very full stomach. The theory that sneezes "blow out" irritants from the nose and/or airways would not seem to explain these causes of sneezing.

There are many facts, myths and folklore associated with sneezing. For fun I will list a few of those here:

- Although most people reflexively close their eyes when they sneeze, some people do have their eyes open, and no, their eyes do not pop out.

- Your heart does not stop during a sneeze.

- Generally speaking, people do not sneeze while they are asleep, although the irritation that initiates the sneeze reflex can awaken someone from sleep.

- Sneezes have been used to commit crimes; so called sneeze-lurkers throw some irritant at the victim and then rob them while they are incapacitated by a bout of sneezes.

- Sneezing has been known to be a symptom of disease and has been suspected as a culprit of spreading illness for centuries. Sayings like "to your health" in response to a sneeze may have come from these observations.

- There are ways to stop a sneeze from occurring, although these do not always work. One way is to scrunch your nose, minimizing the initiating aspect of the sneeze. Another way is to take a slow deep breath, interrupting the reflex action needed to initiate a sneeze. Yet another way may be to use a finger to press the area below the nose and over the top lip (the philtrum).

- Some cultures believed sneezes were a sign from the gods. These may have been interpreted in many ways, and there are stories of how sneezes have influenced history in profound ways (although I cannot speak to the truth of any of these).

- Some cultures believed that sneezes expelled the "breath of life," and so a person's soul would leave their body after a sneeze, possibly allowing the devil to take over. This may be one possible origin of saying "bless you" when someone sneezes.

With the winter upon us, it is important to remember to listen to your grandmother and cover your mouth and nose when you sneeze. Let's stop those 40,000 particles from spreading illnesses.

Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at DrHersh@juno.com.