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A Straight Dope Classic from Cecil's storehouse of human knowledge
06-Sep-1985
Dear Cecil:
Ever since I was a tiny infant, I have sneezed when going out into the bright sun. My
momma confirms this fact, but can't give me a more satisfactory cause than the empirical
statement that I've always done it.
Three decades later, I still produce the obligatory two or three sneezes seconds after
walking into bright sunlight. (It doesn't happen on a cloudy day or at night.)
I remember several years ago reading in the paper that some percentage of people
experienced sun-induced sneezing fits, but they didn't say why. What's the deal? --Alan
C., Dallas
Cecil replies:
You are thinking this is a matter of idle curiosity, Alan? Au contraire--it's a threat to
our national security.
Listen to this frightening headline: "The photic sneeze reflex as a risk factor to
combat pilots," Military Medicine, Breitenbach et al, 1993.
"Photic sneeze reflex" is the medical term for what you've got. Researchers fear
they'll get a guy like you in a screaming dogfight, you break through the clouds into
bright sunlight, you sneeze, your eyes snap shut, and the next thing you know they're
picking you up off the landscape with a rake.
Photic sneeze reflex occurs in something like one-sixth to one-quarter of the population.
It occurs more often in Caucasians than Afro-Americans or Orientals.
According to a Johns Hopkins medic named Stephen Peroutka, the trait is passed along
genetically, with a 50 percent chance of inheritance.
Researchers in Sweden found that out of 460 subjects, 24 percent sneezed in bright light,
and 40 percent had at least one sneezing parent.
Sixty-four percent of children with one sneezing parent were themselves sneezers, but two
nonsneezers never produced a sneezer. (Isn't it amazing how I can make these things so
easy to understand?)
Nobody's exactly sure what causes photic sneeze reflex. I see here in one of the journals
we have an impressive discussion of the role of the trigeminal nerve nucleus.
Basically what this is saying is that you've got a lot of nerves crammed together in the
front of your head, and maybe there can can be leakage of sorts from one nerve pathway to
another. So perhaps the reflex is just a case of congenitally crossed signals.
At this point nobody's prepared to go in there with a pliers and fix it. So your best bet
is to wear sunglasses and stay out of fighter jets.
FROM THE TEEMING MILLIONS
Dear Cecil:
Re "photic sneeze reflex": When we cry, we need to blow our noses. Therefore,
there is a passage from the tear ducts to the nose.
Photic sneeze reflex is caused by tears (our eyes water to protect the unadjusted irises
from bright lights) moving into the nasal passages, tickling the hairs within. The result:
kerchoo! --Peter R., Decatur, Georgia
Dear Peter:
As a matter of fact, there IS a passage connecting the tear ducts to the nose called the
nasolacrimal duct. It enables tears to drain out of the eye.
Some researchers agree that tears leaking into the nose are a possible cause of photic
sneeze reflex.
However, an ear-nose-and-throat specialist I spoke to, who experiences PSR, says sneezing
occurs immediately upon emerging into the light, too quickly for tears to work their way
down the duct.
Once I get all the world's other problems squared away, such as what Steve Miller was
talking about when he sang "I speak of the pompatus of love," I'll get to the
bottom of PSR. (The
Straight Dope: What is the "pompatus of love?" October 25, 1996)
But for right now all I can say is I dunno.
--CECIL ADAMS
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