Why Does Sunlight Make Some People Sneeze ?

  

Gesundheit! You step out into bright sunshine after spending a couple of hours in a dark movie theater and immediately experience a sneezing fit. Does this happen to you often? Does it happen to your children? The Sun induces sneezing in 10 percent of the U.S. population, says Louis J. Ptácek, a neurologist at the Howard Hughes Medical Institute in Maryland and a professor at the University of California at San Francisco. Just how and why this happens, though, has remained a mystery ever since Aristotle raised the question some 2,300 years ago.

      Research suggests that the photi wec sneeze reflex, or PSR, is inherited, but scientists have yet to pinpoint the gene or genes responsible. “There’s precious little known about PSR, and part of that is because it’s not a disease,” Ptácek says. “No one dies from it.”

    One theory is that the gene involved— whatever it is—crosses wires in the brains of those with PSR. For these people, light entering their eyes activates their brain’s visual cortex but also stimulates the motor region that causes the diaphragm to quickly contract, forcing a sharp burst of air out through the nose. NAlthough Sun-triggered sneezing is more of a quirk than a serious condition, Ptácek says, understanding the science behind it could shed light on the underlying biology of other reflex phenomena, such as certain types of epilepsy.