Wednesday 25 August 2010

Ep 135: Why do I sneeze at the Sun?

Do you sneeze at the Sun?

I do. My brother does. Both my parents do. In fact, we are a family of Photic Sneeze sufferers.

The Photic Sneeze Reflex (PSR), also known rather ridiculously as Autosomal Dominant Compelling Helioophthalmic Outburst (ACHOO) Syndrome (how long do you think it took researchers to figure out that acronym....) is a dominant genetic condition affecting around 10% of the population. When a sufferer moves from a region of darkness to a region of bright light - for instance, walking outside and looking at the Sun - multiple sneezes occur. Research into the disorder has yet to explain either its mechanism or an evolutionary reason for why it occurs. One theory is that there is a "short circuit" in the brain, with the stimulated optic nerve somehow triggering the sneeze reflex.

Professor Louis Ptáček runs the Laboratories of Neurogenetics at the University of California, San Francisco. The aim of the lab is to study familial disorders with strong genetic contributions, and thus localise and identify genes that cause human disease. Other conditions in which he is interested include migraine and epilepsy, and an intriguing condition whereby certain sounds cause seizures. He considers PSR to generally be a midly annoying condition, unless you are a combat pilot, where sneezing at the Sun could indeed be life threatening.

I had a really interesting chat to Louis about PSR, and I've left the recording a little longer than usual, as we were really able to explore some fascinating ideas involved with PSR - it was a great chat. Listen in to this show here (or press play below):

Other interesting write-ups of PSR include neurotopia and Scientific American.

This topic came in as part of my call for questions for Science Week, so thanks @lisushi for the question! I'll be putting up more blogs and podcasts to answer the other questions that came in over the next few weeks.

Breitenbach RA, Swisher PK, Kim MK, & Patel BS (1993). The photic sneeze reflex as a risk factor to combat pilots. Military medicine, 158 (12), 806-9 PMID: 8108024 

Langer N, Beeli G, & Jäncke L (2010). When the sun prickles your nose: an EEG study identifying neural bases of photic sneezing. PloS one, 5 (2) PMID: 20169159 

MADIGAN, J., KORTZ, G., MURPHY, C., & RODGER, L. (1995). Photic headshaking in the horse: 7 cases Equine Veterinary Journal, 27 (4), 306-311 DOI: 10.1111/j.2042-3306.1995.tb03082.x

Songs samples in the podcast:
The Steve Wilson Band 
"Stare At The Sun"
from "Sideshows And Fairytales"
Buy at iTunes
DJ Smiths vs Markanera
 "Watching the Sun Goes Down"
from "Watching the Sun Goes Down"
Buy at iTunes
Alexis Cuadrado 
"Bright Light"
from "Puzzles"
Buy at iTunes


  1. MartinhaegenheimMay 01, 2011 8:56 pm

    Hi Marc

    As a photic sneezer from a family of photic sneezers I was very interested to hear your interview with Louis Ptacek, which certainly dispells many of the myths concerning this admittedly marginal physical quirk, in particular about its prevalence. Usually percentages of 20% to 30% are quoted, which, in my experience, are wide of the mark. Even 10% sounds a bit generous to me.

    One point you raised didn't seem to inspire him, but it did ring a bell with me. You asked if it was more common to have multiple sneezes when you have PSR than if not. It's a question I've often wondered about too, as the photic sneezers in my family tend to sneeze several times at a go, whereas the non photics just once. In my case the number of sneezes depends partly on the stimulus. So light coming from both above and below (for example sun reflected on snow or a wet roadway) will generally result in half a dozen sneezes. On the other hand, if I demonstrate the reflex by going out and looking up (just at the sky, not at the sun), I'll usually only sneeze twice. The other PSR members of the family have similar reactions.

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