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Known as Photic Sneeze Reflex, the Act of Sneezing When Looking at the Sun Is Not an Allergy, but a Genetic Condition Affecting Up to 35% of the Population and Intriguing Scientists Since Ancient Greece.
Stepping out of a dark environment and, when looking at the sun, feeling an uncontrollable urge to sneeze. This situation, common for many people, is known as the Photic Sneeze Reflex. Far from being a sign of illness or allergy, it is a hereditary neurological peculiarity, a kind of “short circuit” in the brain that science has been uncovering.
According to an article published in the scientific journal PLOS Genetics, the basis for this reaction lies in our genes. The story to understand why a light stimulus can provoke a sneeze is fascinating and dates back over two thousand years, with observations from the philosopher Aristotle.
What Is the Photic Sneeze Reflex? A Condition More Common Than You Think
The Photic Sneeze Reflex is a condition that affects a significant portion of the world’s population, with estimates ranging from 18% to 35%. It is characterized by a series of sneezes, usually two or three, that occur in succession after sudden exposure to intense light, such as sunlight or a camera flash.
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The technical name for the condition is Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome, which forms the witty acronym ACHOO in English.
The Scientific Explanation: A “Short Circuit” in the Brain
The most accepted hypothesis to explain the Photic Sneeze is that of a “cross-wiring” in the brain. The process would involve two very important cranial nerves:
- The Optical Nerve: Responsible for carrying light information entering our eyes to the brain.
- The Trigeminal Nerve: Responsible for facial sensations, including those of the nasal mucosa. It is the nerve that triggers the sneeze reflex when there is irritation in the nose.
The theory is that, in some people, these two nerves are very close together. When a strong and sudden light intensely activates the optical nerve, the electrical signal “leaks” and stimulates the trigeminal nerve. The brain then interprets this stimulus as if it were a physical irritation in the nose, like dust, and triggers the sneeze as a defense mechanism to expel a “invader” that does not exist.
An Hereditary Characteristic: The Genetics Behind the Sneeze
Science has already confirmed that the Photic Sneeze Reflex is an autosomal dominant genetic characteristic. This means that it only takes inheriting a single copy of the gene from one parent to manifest the characteristic. If one of your parents sneezes in the light, you have a 50% chance of inheriting this peculiarity.
A genome-wide association study published in 2010 by Nicholas Eriksson and other researchers was a milestone. The research identified a strong link between the reflex and a specific marker, rs10427255, located near the ZEB2 gene on chromosome 2.
An Ancient Curiosity: The First Observations from Aristotle to Francis Bacon
The phenomenon has intrigued humanity for centuries. The first known record comes from the Greek philosopher Aristotle in the 4th century BC. In his work Problemata, he questioned why looking at the sun caused a sneeze. His theory was that the heat of the sun warmed the nose, causing a reaction.
Centuries later, in the 17th century, the English scientist Francis Bacon also investigated the reflex. Unlike Aristotle, Bacon noticed that if he looked at the sun with his eyes closed, the sneeze did not occur. He correctly concluded that the cause lay in the eyes, not in the warming of the nose.
The Modern Discovery: How Science Understood the Reflex
The modern scientific study of the Photic Sneeze Reflex gained momentum in the 1950s when French researcher Jean Sedan noticed that some of his patients would sneeze when exposed to the light of an ophthalmoscope during retinal examinations.
It was in 1978 that Dr. W.R. Collie and his team created the acronym ACHOO, highlighting the hereditary nature of the condition. The popularization of the term and the deepening of studies, such as that of Dr. Stephen J. Peroutka in 1984, helped consolidate the understanding we have today of this fascinating and harmless peculiarity of the human body.
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