Suddenly sneezing uncontrollably when stepping outside from a dark space (like a movie theater or enclosed room) shouldn’t be a cause for alarm. This phenomenon affects about 25-30% of the global population, and scientists have named it: photic sneeze reflex.
Why does looking directly at the sun make some people sneeze?
Although this strange phenomenon has been observed for a long time, experts only recently discovered the mechanism behind the photic sneeze reflex.
Initial Hypotheses
The great Greek philosopher Aristotle posed a question in the first chapter of his work, The Book of Problems, around 350 BC: “Why does the heat of the sun cause sneezing?” This is considered the first evidence of the phenomenon known as “photic sneeze reflex.” At that time, Aristotle hypothesized that the heat of the sun created moisture and sweat inside the nose and mouth, leading to increased secretion. To relieve this moisture, the body compels us to sneeze.
It wasn’t until the 17th century that philosopher and scientist Francis Bacon began exploring the mysteries surrounding the human sneeze reflex. He disproved Aristotle’s theory by looking at the sun with his eyes tightly shut. As a result, he experienced no sneezes at all. Therefore, he suggested that looking at the sun causes tears to flow, which then trickle into the nose and trigger sneezing.
However, scientists later disagreed with this view, simply because sneezing occurs too quickly after exposure to light, and producing tears takes a certain amount of time.
The Mystery Unfolds
In 1964, a new study yielded promising results, demonstrating that the photic sneeze reflex is actually a genetic trait. If one parent experiences this condition, there’s a 50% chance their children will also exhibit signs of the photic sneeze reflex.
In 1978, Dr. Roberta Pagon and her colleagues made further strides in their quest to understand this unique phenomenon.
During a conference on congenital defects, the issue of the photic sneeze reflex was raised. After a quick survey, 4 out of 10 doctors in the discussion reported that they and their families were very prone to sneezing when directly exposed to sunlight. Moreover, the occurrence of multiple consecutive sneezes was consistent among family members but varied across different families. Dr. Pagon described this, stating: “One person said most of their family sneezes continuously 5 times, whereas my family does it 3 times, and another person only 1 time.”
This provided an important clue leading to a final conclusion. After collaborative research, scientists were able to accurately name this puzzling phenomenon: ACHOO Syndrome.
ACHOO Syndrome
So, what happens in the body that leads to this strange symptom? In 2010, a study conducted by Professor Nicholas Langer of the University of Zurich (Switzerland) attempted to decode ACHOO by examining the brain responses of those who sneeze due to sunlight and those who do not have this syndrome.
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The trigeminal nerve sends signals to the brain when the nose is stimulated.
Using an electroencephalogram (EEG), Dr. Langer found surprising results: “The photic sneeze reflex is completely different from typical reflexes, which occur only at the brainstem or spinal cord. It seems to involve other cortical areas as well.” Based on observations from the EEG, he proposed two hypotheses on why sneezing occurs due to sunlight.
The first hypothesis suggests that the visual system in the brains of those with ACHOO syndrome is much more sensitive than in average individuals. Excessive light causes other parts of the brain, including the somatosensory system known to control sneezing, to become chaotic. Additionally, another hypothesis he proposed is somewhat more complex but aligns closely with Aristotle and Bacon’s concepts.
According to Dr. Langer, a sneeze due to light also forms when our nose is stimulated by some cause. The trigeminal nerve (cranial nerve V) is responsible for managing the body in response to this stimulus. When exposed to sunlight, the trigeminal nerve (located next to the optic nerve) sends visual information from the retina to the brain.
Therefore, if sunlight suddenly shines directly into our eyes, the retina is unexpectedly exposed to a high amount of light, and the optic nerve will send signals to the brain to instruct the pupil to constrict. Theoretically, this signal can be perceived by the trigeminal nerve, leading the brain to mistakenly interpret it as stimulation to the nose, resulting in one (or multiple) sneezes. Currently, these two perspectives proposed by Nicholas Langer are the most widely accepted in the scientific community.
This syndrome typically occurs after exposure to bright light, such as sunlight, and most often happens when moving from darkness to light, such as when turning on a light in a dark room. Dr. David Lang, Chair of the Allergy and Clinical Immunology Department at the Respiratory Institute at Cleveland Clinic, told Live Science: “It is not triggered by a specific wavelength of light but rather by a change in light intensity.”
“The severity of the sneeze reflex can vary from person to person. For some, the photic sneeze occurs only occasionally. For others, bright lights can trigger uncontrollable sneezing in rapid succession,” noted the Cleveland Clinic.
The severity of the sneeze reflex can vary from person to person.
In a 2010 study, researchers at the genetic testing company 23andMe in California discovered two mutations related to light-induced sneezing. Additionally, a 1995 study in Alabama found that light-induced sneezing could also be associated with a deviated septum. Meanwhile, a 2019 study in Japan identified a potential link between this reflex and migraines.
Dr. William Howland, medical director of Clinical Research Orion in Austin, stated: “Although it may increase the risk of accidents on highways or if you’re performing acrobatics or in suburban areas, it is generally completely harmless. The primary way to manage this reflex is to wear sunglasses when outdoors. Antihistamines, which typically affect allergies, do not affect this reflex,” he added.
Howland mentioned: “Another potential way to prevent sneezing when exposed to sunlight is to apply pressure to the philtrum, the groove under the nose, with your finger horizontally. “It’s like giving yourself a mustache with your finger.” A 2019 study in Australia showed that this pressure could alleviate the stimulation that the trigeminal nerve might encounter from bright light or hinder neural signals that could activate light-induced sneezing.
