13 mars 2023
A sudden passage from shadow to light, and it is the sneeze: this is the photo-sneeze reflex, which is also called heliotropic sneeze or photic sneeze reflex. This physiological phenomenon affects one in four people.
In English, the photo-sneeze reflex is known by the acronym ACHOO (for Autosomal dominant Compelling Helio-Ophthalmic Outburst). It therefore results in one or more sneezes as soon as you move from shade to light, most often from the sun. But a simple bright light can also trigger serial “atchoum” in a significant part of the population.
To definitively pierce the mystery of this curious reflex that has intrigued since Aristotle (“Why do we sneeze more when we look at the sun? »he wonders in one of the texts of his Problems), British researchers even launched a survey in October 2020, The Oxford Photic Sneeze Survey.
Nearly 2,000 people answered questions online regarding the color of their iris, the time spent outdoors, their sensitivity to light, their chronotype (early riser? night owl?), their possible allergies, the lighting conditions that cause a sneeze… With their answers, the researchers will design “a laboratory stimulus to examine the aspects of wavelength and intensity that cause photic sneezing in order to refine the underlying retinal mechanisms”.
trigeminal nerve
These experiments will perhaps make it possible to validate one of the most widespread hypotheses, according to which, in certain individuals, an anomaly of the trigeminal nerve is responsible for the photo-sneeze reflex. The trigeminal nerve is in fact on the path of the optic nerve, which transmits to the brain the electrical signal resulting from the conversion of light by the retina.
In people with the photo-sneeze reflex, the nerve fibers of the optic and trigeminal nerves would indeed be closer than average: the stimulation of the optic nerve in contact with a brutal and sudden light, as when going from shadow in the light, would thus cause a kind of interference with the trigeminal nerve… which would trigger the sneeze reflex.
Genetic
This trait is inherited in an autosomal dominant fashion, says the US Center for Biotechnology Information (NCBI). In other words, “If a parent is affected, their child has a 50% chance of inheriting the syndrome”. If it is not dangerous as such, it can on the other hand have unfortunate consequences, such as “the possibility for drivers to have an accident caused by sneezing caused, for example, by exiting a road tunnel on a sunny day”.
To protect yourself once morest this, it is therefore recommended to wear a hat and sunglasses to protect your eyes from direct sunlight, whenever possible.
