Photic sneeze reflex is a dominant genetic trait which causes sneezing when one is suddenly exposed to bright light. It is also referred to as photic sneeze response, sun sneezing, photogenic sneezing, the photosternutatory reflex, and Autosomal Dominant Compelling Helio Ophthalmic Outburst syndrome (ACHOO). The first mention of the phenomenon is in later work attributed to Aristotle.
Experiments to determine exactly how the photic sneeze operates are difficult to perform. Theories go back at least to Francis Bacon’s 1635 musings on moisture leaking from the brain, but the modern consensus is that the mechanism is neurological.
The eyeball, tear glands, sinuses and facial skin all are sensorally linked by the ophthalmic nerve. It runs up the sinuses and into the ophthalmic ganglion, a wad of nerve cells in the back of the eye very near the optic nerve.
When the optic nerve is stimulated by bright light, we feel discomfort or even pain. In photic sneezers, some of this stimulation somehow jumps to the ophthalmic ganglion and down the ophthalmic nerve, which experiences the stimulation as phantom irritation of the nose. It responds as it always does to nasal irritation by setting off the sneeze reflex.
Another theory suggests that tears leaking into the nose through the nasolacrimal duct are a cause of the photic sneeze reflex. The speed of the reflex seems to favor the first theory, as it happens much too quickly for tears to be generated and drain into the nose. In addition this sneeze reflex can be brought on by a sudden inhaling of cold air or a strong flavor such as a strong mint gum. This implies an overstimulation of any nerve close to the trigeminal nerve causing the sneeze reflex.
About 20 percent of the population are photic sneezers of varying sensitivity. They will sneeze when they see any bright light, typically when moving from a dark area into a brightly lit one. Leaving a movie theater on a summer day is a classic set up. Some photic sneezers say sneezing while driving out of a tunnel or from shadow into sunlight, is a hazard.
The number of sneezes varies from person to person, but for any given person remains about the same. The sneezing can be repeated ad infinitum by repeated exposure to bright light. Some photic sneezers have learned they can help along a regular, dust induced sneeze by looking at an electric lamp.
In tests, some photic sneezers could consciously restrain the sneezing, especially when they knew bright light was coming. No particular wavelength of light was more inductive, and sunglasses eliminated the effect. An Ohio State University Medical Center doctor has noted that after he removed a patient’s eye, she could touch a spot in the socket and induce sneezing at will.
Photic sneezing has been documented in three successive generations of a single family and may be genetically determined. It appears to occur more frequently in Caucasians. The same phenomenon may affect horses, which are sometimes afflicted with headshaking, a syndrome of snorting, sneezing, bucking and shaking that can render them unrideable.
In a study of 138 patients treated for different types of allergic rhinitis (runny nose) 15 of these also had solar sneeze reflex. Antihistamine, decongestant and other therapy improved the condition, and seven of the 15 also reported improvement in their solar sneezes.
Some have suggested that solar sneezes may be a particular problem for baseball outfielders, airplane pilots, bus drivers and high wire acrobats, for whom a solar sneeze may be more than just a light matter.