Does looking at bright lights suddenly — like staring at the sun — induce a bout of sneezing for you? If so, you may have a photic sneeze reflex (PSR), or photosneezia, as it is more colloquially known.

Also called the Autosomal Dominant Compelling Helio-ophthalmic Outburst, or the ACHOO syndrome, this reflex is different from regular sneezing, which is often triggered by allergies, irritants, or simply a cold. PSR affects 17-35% of the world’s population — so, potentially, one in three people could end up experiencing it, according to a BBC report. Moreover, out of those who experience it, 67% of them are females.

While PSR may seem like a harmless, albeit bizarre, phenomenon, it renders people vulnerable to considerable risks. For instance, reflexive sneezing can be dangerous to an automobile driver emerging from a tunnel; since a series of sneezes can force one to shut their eyes involuntarily, it could potentially lead to traffic accidents.

“…you have other safety-critical professions in which sneezing in response to bright light isn’t helpful, like fighter pilots or truck drivers, anywhere you can’t really lose control of something,” Manuel Spitschan, an experimental psychologist at the University of Oxford, told The Guardian.

The cause of PSR remains unknown, and researchers have been unable to find any evolutionary function it could potentially be serving, either. What we do know, however, is that PSR may be genetically inherited from one’s biological parents — having one parent with PSR, puts one at a 50% chance of inheriting it; and having two parents with PSR ups the likelihood to about 75-100%.

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Researchers have hypothesized that the phenomenon could be a result of ‘crossed wires‘ in the trigeminal nerve in the brain, which receives sensory stimuli from both our eyes and nose. “The thought is that this really active stimulation of the optic nerve may cross over… causing that little tickle which gets you to sneeze,” Derek Muller, a YouTuber with a degree in physics, explained. Basically, stimulation of the optic nerve due to light exposure can result in a tickling sensation in the nose, inducing a sneeze, biology seems to show.

Scientists have also found significant correlations between these inexplicable barrages of light-induced sneezing and living with a deviated nasal septum. In addition, a 2010 study on human genotypes also indicated a biological link between PSR and light-induced epileptic seizures.

Since October 2020, the Department of Experimental Psychology at the Oxford University is trying to uncover the more layered ‘why’ behind PSR. “We know it’s only bright light that triggers it, but wavelength [of the light] might also be a factor… Once we know that, we can start to unpick the retinal mechanism, so is it going through the rods or cones [photoreceptors in the human eye] or something else?,” Spitschan, who was involved in the study, said.

However, it may be some time before these questions are answered. Curiously, the earliest record of people trying to understand the reflex dates back to ancient Greek philosopher Aristotle’s times; he wisely wonders in his third-longest work, the Book of Problems: “Why does the heat of the sun provoke sneezing?”