A 21-year-old man wore a light sensor on a necklace for a month and logged every sneeze. Over 30 days, he recorded 82 sneezing episodes, about 2.7 a day. In most of them, the light around him had just jumped sharply.
The man is Lucien Bickerstaff, first author of the study in F1000Research and its only participant. He has the photic sneeze reflex, and he and colleagues at the Technical University of Munich and the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, set out to measure it in daily life instead of relying on what people remember. The paper first appeared in October 2025, and a revised, peer-reviewed version followed in March 2026. The data were collected in the summer of 2022.
The reflex is often nicknamed ACHOO syndrome. The authors write that it reportedly affects up to around 20% to 30% of people. Yet in a 2025 review, the same group noted that no study had examined how specific light conditions relate to the sneeze.
A Tenfold Jump in Brightness Came Before the Sneezes
From July 12 to Aug. 10, 2022, Bickerstaff wore a light logger that took a reading every 30 seconds. He recorded each sneeze in a phone app, noting the time and the number of sneezes. Each episode had between one and six.
The researchers compared the light a few minutes before each episode with the light at the moment it happened. On average, it rose from about 527 lux, roughly the brightness of a well-lit office, to about 5,349 lux, closer to outdoor daylight on an overcast day. The median rise was about tenfold, and the difference was statistically significant.
When he sneezed, light levels almost always stayed above 500 lux. During 100 randomly chosen stretches with no sneezing, they mostly stayed below that level. The authors wrote that «sneezing often took place during transitions in environment, i.e., walking from home to the bus station, or from the bus station to the workplace.»
Not every sneeze fit the pattern. Before seven of the 82 episodes, the light actually dropped, a reminder that other, uncontrolled factors in the environment can set off a sneeze too.
The Lab Couldn’t Make Him Sneeze Even Once
Next the team brought him into the lab. He sat through more than 150 controlled bursts of light, some as bright as 17,600 lux, while an eye tracker measured his pupils.
His pupils shrank more as the light got brighter, as expected. He also felt a tickle in his nose that grew stronger with brightness, and at the highest levels some tickles were rated 10 out of 10.
He did not sneeze once.
The authors point to differences between the lab and the outdoors. The lab light contained no ultraviolet component, and temperatures differed from real-world conditions. They concluded that the experimental approach «is promising with further refinement.» For now, everyday life provoked the reflex better than the lab did.
The mismatch also feeds an old puzzle. Sneezing normally runs through the trigeminal nerve, which senses irritation in the nose, while light travels a separate visual pathway. Manuel Spitschan, the study’s senior author, told The Scientist that «light information is not something that the trigeminal nerve, which usually underlies sneezing…is interested in.»
A Quirk for Most People, a Hazard on the Road
Earlier research offers clues to the mechanism. A 2010 University of Zurich EEG study in PLoS One found heightened excitability in the visual cortex of photic sneezers. The same year, 23andMe researchers reported in PLoS Genetics that the trait was associated with a genetic variant near a gene called ZEB2. A National Library of Medicine summary of ACHOO syndrome, last updated in 2015, says the trait is inherited in an autosomal dominant manner but that its genetic basis is «not yet known.»
«Most people who have it see it as a quirk…rather than something that is debilitating,» Spitschan told The Scientist.
That is usually true, but not always. The NLM summary warns that drivers exiting a road tunnel on a bright day, as well as airline pilots, may be at risk. A case report in the April 2026 issue of the American Journal of Emergency Medicine described a 26-year-old delivery rider in India who had bursts of 10 to 15 sneezes, set off by sunlight and by tooth brushing. As he rode out of a covered parking area into midday sun, a sneezing fit hit, and his face struck a concrete pillar. It was his third crash in three months, all linked to moving from shade into bright light. He fractured the orbital floor, the thin bone under the eye, and needed surgery. Allergy tests were negative, and doctors diagnosed photic sneeze reflex.
The sudden jumps in brightness captured in the new study describe the same kind of moment.
One Sneezer Is Not a Population
The biggest limitation is the sample: one person, who was also the lead author, with no comparison participants. The sensor hung on his torso rather than at eye level, and the authors acknowledge that «it is very easy for the participant to block the light logger with a jacket, arm, or bag.» Temperature was not measured, sneeze times were self-reported, and he was never examined by an eye, nerve, or ear, nose, and throat specialist.
The tenfold figure is therefore a starting point for research, not a rule for everyone who sneezes in the sun. Spitschan told The Scientist that «cataloging the [natural] conditions under which the sneeze occurs…is a good start.»
There is no drug treatment for the reflex. The NLM summary mentions shielding the eyes with a hat or sunglasses. Anyone whose sneezing fits come on while driving, cycling or operating machinery should talk with a clinician.
Key Questions Answered
What is the photic sneeze reflex?
It is an inherited reflex in which sudden exposure to bright light, such as stepping into sunlight, sets off one or more sneezes. It is also called ACHOO syndrome.
How common is it?
Estimates vary. The study’s authors say it reportedly affects around 20% to 30% of people.
What did the new study find?
In one photic sneezer tracked for 30 days, light levels rose by a median of about tenfold between the minutes before a sneezing episode and the moment it happened. Light almost always stayed above 500 lux when he sneezed.
Why couldn’t researchers trigger sneezes in the lab?
Bright lab light caused strong nose tickles but no sneezes. The authors note that the lab light lacked ultraviolet light and that temperatures differed from real-world conditions.
Is the reflex dangerous?
For most people, it is a harmless quirk. But sneezing fits can be risky while driving or flying, and a 2026 case report linked repeated photic sneezing to a delivery rider’s crash.
Do the findings apply to everyone with the reflex?
Not yet. The study involved a single participant with no comparison group, so larger studies are needed.
Published by Medicaldaily.com
