SNEEZING AT THE SUN - THE PHOTIC SNEEZE REFLEX EXPLAINED

Sneezing as the result of being exposed to the sun or bright lights is a genetic quirk that is still unexplained by science, even though it has intrigued some of history's greatest minds such as Aristotle and Francis Bacon.

On the face of it, uncontrollable sneezing  in response to numerous stimuli, such as looking at bright lights or the sun —known as the photic sneeze reflex— appears to be an unusual affliction. Unusual often translates as rare. However, I discovered on Sunday that it actually affects up to one third of the population! Even at the lower end of the scale for numbers affected, 10% may be affected due to the trait being autosomal-dominant according to one study in the 1960s. This means that the gene is neither on the X nor Y chromosome and only one copy of the gene has to be present for the trait to be expressed.

Listening to the radio at the weekend, I was reminded of this condition that I had come across in the past, but not really understood. The standard scientific website of wikipedia demonstrated there existed an almost comedic acronym, namely ACHOO (Autosomal Dominant Compelling Helioophthalmic Outburst Syndrome ) yet I then found a scientific journal paper by Swiss researchers Langer, Beeli & Jancke in 2010 describing their electroencephalographic studies-and this also remarkably noted this acronym!

Ultimately they proposed in the conclusion that that the photic sneeze phenomenon might be the consequence of higher sensitivity to visual stimuli in the visual cortex and of co-activation of somatosensory areas. So effectively, there are crossed wires in the brain are probably responsible for the photic sneeze reflex. A sneeze is usually triggered by an irritation in the nose, which is sensed by the trigeminal nerve, a cranial nerve responsible for facial sensation and motor control. This nerve is in close proximity to the optic nerve, which senses, for example, a sudden flood of light entering the retina. As the optic nerve fires to signal the brain to constrict the pupils, the theory goes, some of the electrical signal is sensed by the trigeminal nerve and mistaken by the brain as an irritant in the nose. Hence, a sneeze!

READ their paper:  Photic Sneezing Study Langer et al 2010