MadSci Network: Neuroscience
Query:

Re: How big does a particle have to be to make me sneeze

Date: Mon Jan 3 08:19:49 2005
Posted By: Art Anderson, Senior Scientist in Immunology and Pathology at USAMRIID
Area of science: Neuroscience
ID: 1104596951.Ns
Message:

Dear No Name, No School, etc.,

You ask about how big a particle need be to stimulate a sneeze when it 
gets onto the mucus membranes of your nose.

This is an interesting question. First because it presumes that the nose 
is a transducer of mechanical stimuli and second because it presumes that 
there must be threshold to trigger a response.

Actually, neither of these are probably correct. The mucus membranes of 
the nose trap fairly large particles without triggering a sneeze....at 
least before the specific properties of the particle begin to stimulate an 
inflammatory or irritant reaction.

It is the irritation and inflammation induced by the particle that 
stimulates the sneeze, not the particle itself.

Pollens, house dust, and other particles are usually harmless, but when 
they irritate the nose the body responds by expelling them from the nasal 
passages. We breath in pollen grains all the time without sneezing. 
However, if the pollen you breathed in the past stimulated an allergic 
immune response; and, you have IgE antibodies against the pollen or dust 
antigens, then the next time that species of pollen touches your nasal 
mucus membranes it will trigger a cascade of immune reactions culminating 
in activating mast cell secretion. The cytokines (drug like hormones) and 
histamine released by these mast cells will cause quick swelling and 
increased mucus secretion in your nose and Hacchhoooo you will sneeze. 
But, the sneeze will have been caused by this reaction to the pollen, not 
by the size or weight of the pollen grain.

The nose mistakes strong odors, sudden chills, and even bright lights (see 
photic sneeze reflex) for parasites, and it tries to defend itself with a 
sneeze. None of these stimuli are particles yet they too stimulate 
sneezing either because the chemicals in strong odors or sudden chills 
directly irritate, or the bright lights stimulate a neurological reflex 
that results in a sneeze. It always amazes me that the speed of air coming 
out of the nose or mouth during a sneeze is over 100 miles per hour and 
the force is usually sufficient to expel pretty big bits of mucus, help 
drain plugged paranasal sinuses, and shoot out a parasitic worm if it 
happens to have crawled into your nose. Johnny Carson used to talk of the 
bird of paradise flying up a nose but he was just being silly....I think.

Here are some other answers about what triggers a sneeze.
 http:
//www.madsci.org/posts/archives/sep99/938695934.Gb.r.html
 http://www.people.
virginia.edu/~rjh9u/sneeze.html



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