Ever stepped out into bright sunshine and immediately felt a sneeze coming on? You’re not alone. Many people experience this peculiar reaction, often wondering, “Why Do I Sneeze When I Look At The Sun?”. This isn’t an allergy to sunlight, but rather a fascinating and harmless condition known as the photic sneeze reflex.
This seemingly strange phenomenon, where bright light triggers a sneeze, has been observed for centuries. Even the ancient Greek philosopher Aristotle pondered this very question. However, it wasn’t until 1954 that scientists formally documented it in medical literature. Today, researchers sometimes playfully refer to it with the acronym ACHOO: Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome.
“It’s not a disease,” clarifies Louis Ptáček, a neurologist and human geneticist at the University of California, San Francisco. “Some people find it annoying, but some people like it to some extent. They’ll say, ‘It helps me get a sneeze out.’” Indeed, for most, it’s just a quirky, involuntary response to bright light, not a cause for concern.
The photic sneeze reflex is characterized by sudden sneezing, sometimes a single burst and sometimes multiple sneezes in a row, when a person adapted to dim light is abruptly exposed to intense light. Sunlight is the most common trigger, but even artificial light sources like light bulbs or camera flashes can induce a sneeze. Interestingly, there’s a “refractory period” – a yet undefined duration of time spent in darkness required before the reflex can be triggered again by light.
It turns out that you are in good company if you’re a sun sneezer. It’s estimated that a significant portion of the population, between 10 to 35 percent, experiences the photic sneeze reflex. The prevalence is higher in families with a history of the condition, suggesting a genetic component. Scientists believe it’s likely an autosomal dominant trait, meaning only one parent needs to carry the gene for it to be passed on.
Ask your parents about ACHOO – you might be surprised to find it runs in the family!
A person experiencing the photic sneeze reflex, sneezing due to bright sunlight exposure. Understanding this reflex helps explain why some people sneeze when they look at the sun.
To understand why bright light triggers sneezing, it’s helpful to first understand the mechanics of a regular sneeze. A typical sneeze is a powerful reflex action designed to expel irritants and protect our respiratory system. When irritants like dust or pepper enter the nasal passages, they stimulate the nasal mucosa, triggering a sneeze to forcefully eject these foreign particles. It’s a remarkably effective defense mechanism, expelling up to 40,000 microscopic particles at speeds reaching 85% of the speed of sound!
“When we sneeze, there is a huge contraction of the diaphragm all at once,” Ptáček explains. This forceful expulsion is our body’s way of clearing the airways of unwanted substances.
But the question remains: why does bright light initiate this same powerful reflex in some individuals? Is it some evolutionary quirk, perhaps a signal to protect sensitive skin from the sun? While the exact reason isn’t definitively known, the leading theory points to a neurological “cross-wiring” between the trigeminal nerve and the optic nerve.
The trigeminal nerve is responsible for facial sensations, including that itchy feeling in your nose that precedes a sneeze. The optic nerve, on the other hand, is responsible for vision and causes the pupils to constrict in response to bright light. The theory suggests that in people with photic sneeze reflex, the signals from the optic nerve, triggered by sudden bright light, mistakenly activate the nearby trigeminal nerve, leading to a sneeze.
While this “crossed-signals” theory is the most widely accepted, definitive large-scale studies are still lacking. Much of the research on photic sneeze reflex is based on smaller studies, often focusing on single families or small groups of individuals who experience sun sneezing.
For instance, a 2010 study conducted in Switzerland using only ten photic sneezers revealed heightened activity in the primary and secondary visual cortex – brain regions processing visual information – when exposed to various wavelengths of light. This supports the idea that the visual pathway is indeed involved. Conversely, Spanish researchers in 2016, studying thirteen individuals from the same family with the reflex, discovered thicker corneal nerves. These nerves connect to the trigeminal nerve, offering another piece of the puzzle.
Individuals shielding their eyes from the sun. Understanding the photic sneeze reflex is crucial, especially in professions where sudden sneezing due to sunlight could pose a risk.
Despite being a widespread phenomenon, research into photic sneeze reflex remains limited, primarily due to funding constraints. As Ptáček notes, “It’s hard to get funding because reviewers don’t think of it as a problem.” Funding is often directed toward more conventionally perceived “problems” like Parkinson’s and multiple sclerosis.
For most people, sun-induced sneezes are harmless and merely a momentary quirk. However, the combination of temporary vision impairment from bright light, the involuntary sneeze itself, and the subsequent eye closure could present risks in specific situations. Case studies suggest potential hazards for professions like high-wire acrobats, baseball outfielders, and combat pilots. Even in everyday life, a sneeze triggered by sunlight when driving out of a dark tunnel can be momentarily disorienting.
Despite its seemingly trivial nature, studying the photic sneeze reflex could offer valuable insights into broader neurological mechanisms and reflex disorders like epilepsy. Ptáček believes that identifying the genes responsible for photic sneeze reflex could unlock fundamental understandings of reflex disorders in general. Sometimes, the most significant breakthroughs in medicine come from unexpected avenues of inquiry.
Grow your mind and keep exploring the fascinating mysteries of the human body!
