Why Do We Sneeze When We Look at the Sun?

A recent Scientific American on-line article discusses recent speculation on the photic sneeze reflex (PSR) - the reflex many people have to sneezing when staring at a bright light.

The article itself describes theories about the mechanics of this reflex, e.g., interfering nerve pathways leading to the brain, but there is no thought given to what evolutionary benefit, if any, there may be behind PSR. Several commentators observe that babies especially seem prone to this effect. I certainly noticed this myself: whenever I opened the shades in my children’s room in the morning they would almost invariably let out a sneeze - especially if they had a cold.

Here’s my theory: I assume that this reflex evolved as a way for young children to clear their nasal passages in the morning at the first light of day. In a time of no artificial lighting, the bright morning sun would be a good trigger for a young baby to clear mucus that had gathered throughout the night - like clearing the sand out of its eyes. That the PSR persists through adulthood is just a side effect of this; it certainly isn’t harmful and probably has some minor benefit.

Or course proving this is another matter entirely: is there any actual benefit to be had? I’ve always felt that this sort of evolutionary speculation is the last bastion of the arm-chair natural philosopher. If it can be shown that young children (those less able to clear their nasal passages themselves) actually have a higher incidence of this reflex, that would provide at least some clue that this is correct.

» Posted: Sunday, January 27, 2008 | Comments (9) | Permanent Link


alas, none of us has this trait at our house… does it mean we’re more evolved?

» Posted by bethany on February 7, 2008 10:12 PM

That’s too bad; I think it comes in pretty handy sometimes.

You may be right - this trait could be some sort of a throw-back: I had extra wisdom teeth which is probably some other simian anachronism.

Maybe though people with Nordic genes are less prone to this because of the wider range in seasonal daylight in the homeland. Or it could just be a simple cross-wiring like the SciAm article hinted at. A book I recently read described how tangled up the cranial nerves have become in the evolution from the simple layout in fish to our knobby human heads.

» Posted by winter on February 12, 2008 08:28 PM

I always thought it was to prevent us from burning our retina by making us look elsewhere when you stare at the sun.

» Posted by Anonymous on March 12, 2008 01:51 PM

wow cant beleive this my brother actually has this, he said he was allergic to the sun and i just called him a loser lol I was wrong

» Posted by nas on July 10, 2009 06:13 AM

» Posted by David S. on November 13, 2009 08:47 AM

I have notice that this happends to me only if I look up with my neck stretch.

» Posted by Anonymous on February 17, 2010 05:03 PM

Why do we use the Sun as ammunition so as to make us sneeze?

» Posted by Anonymous on May 16, 2010 04:22 PM

This happens to me all day, nit just in the morning

» Posted by Johny on November 21, 2010 11:07 PM

This is handy most of the times for me. I’m trying to sneeze but I can’t. I look at the sun then it’s done. All my family benefit from it

» Posted by Anonymous on September 13, 2011 04:40 AM