Sneezing... is an involuntary reflex, controlled by an unconscious part 
of the brain. It's purpose- to clear irritants and allergy-producing substances 
such as viruses and bacteria out of the nose. Allergist Tom Adler- 

ADLER: when you sneeze there's a sudden expulsion of air through the nose and mouth. 
A variety of nerves are stimulated and involuntarily you build up pressure in your 
diaphragm and chest and then open up the soft palate to allow the air out suddenly 
though the nose and mouth. The sneeze reflex does include watering of the eyes, the 
eyes close. The nasal passageway becomes congested with blood and narrows down so 
your breathing through your nose gets a little more labored and you feel congested 
and stuffy. 

    Explaining away sneezing as a reflex has unglamorized sneezing quite a bit. 
Ancient folk believed in the benefits of sneezing, induced through different 
tobacco based preparations- later called snuff. 

ADLER: Indians and Indian cultures have felt that sneezing was a good thing, a source 
of enjoyment actually, and if a person couldn't sneeze that was an unhappy event for 
them. And ancient Greek philosophers thought sneezing to be a divine sign of great importance. 
They thought that sneezing came from the head and that's where the soul
resides- it must represent something divine. Hippocrates built on the beliefs of 
ancient Jews in noting that sneezing could be dangerous- particularly in association 
with lung and respiratory ailments- bear in mind this was before anti-biotic 
and infections were a major cause of death. 

    The practice of saying "bless you" when someone sneezes may have originated in 
600 AD, when the first plague epidemic hit Rome.

ADLER: There's a form of plague that takes your life within hours and one of the popes
died sneezing. And we still have that form of plague around today actually, though very
rare. After this particular pope died, then Gregory the Seventh ordained that people 
must say "god bless you" to summon divine intervention over the dreaded affliction that
might follow.

    Other than physical provokers- those entering the passageways- some are caused to
 sneeze from bright light or from pressure on the jaw or forehead. The repetitive sneeze 
is usually associated with allergies, causing a constant irritation, and thus, the 
reflex. There are isolated reports of those unable to stop sneezing. The Guinness Book 
of World Records credits one woman with the longest sneezing spree of 979 consecutive days.

ADLER: One can try to attack the cause- separate yourself from irritants- and try to not
to get in close proximity to the sources of the allergies, like animal dander, dust,
molds and mildew or pollen. But there isn't anything much that we can offer for sneezing
from infection. Primarily because most of the infections are viral infections.
And you don't know your own strength, because when squelching a sneeze you're holding 
up a blast that can reach well over 100 miles per hour. 

ADLER: There are case reports of bad things happening to people during the act of 
sneezing related to the great increase of pressure in the chest. There's a handful 
of cases of strokes and various kinds of vascular phenomenon where people blow out a 
blood vessel in their brain or chest or somewhere as a result of sneezing.

    Adler admits exactly what causes sneezing remains a medical mystery.

ADLER: There's a whole population of people that sneeze and have nasal complaints but
don't have allergies. They sneeze with cold air, they become congested and their nose 
runs inappropriate times and their prone to sinus infections and other sinus complaints.
There's an appreciation that nerve endings themselves are little store houses of chemical
information. And I think we're getting to learn more about all the chemical messengers
that come out of these nerve endings that can produce a lot of symptoms that we'd
ordinarily explain because the person is not having a cold and their not having
allergies. 

    Allergist, Tom Adler. Bill Flynn, WXXI-1370.