Do you sneeze when you see light? Solving the mystery of the 'photic sneeze reflex'

◇ Origin: Where does the connection between light and sneezing come from?

Have you ever experienced this? You step out of a dark room, look at the sunlight, and immediately sneeze—"Achoo!" Whenever I feel like I'm about to sneeze but can't, I look for a light source and stare at it. As it turns out, this is a phenomenon known as the "photic sneeze reflex." It is called the "photic sneeze reflex" in English, and about one in four Japanese people have this trait. Since when has this strange reaction been known? In fact, the ancient Greek philosopher Aristotle recorded around 350 BC that "some people sneeze when they look at the sun." He seemed to think that "the heat of the light might be irritating the nose." However, modern science has discovered a different reason. It is an interesting relationship between the nerves that connect the eyes and the nose.

Data: A survey by Kagoshima University (1992) found that out of 749 people, about 25% answered that they sneeze due to light. Source: Satoshi Kuchiiwa Research, Kagoshima University

◇ Transition: The mechanism revealed by science

So, why do we sneeze when we see light? The key lies in the nerves within the brain. When light enters the eye, the "pupillary light reflex" is triggered, causing the pupils (the black part of the eye) to constrict. The nerve that sends this signal is called the "oculomotor nerve." However, this signal can sometimes accidentally jump to the "trigeminal nerve," which controls sensation in the nose. It's like a telephone line getting tangled and connecting to someone else. In science, this is called "neural crosstalk," and it is thought to be caused by signals getting crossed in the hypothalamus or brainstem. The nose mistakenly thinks "something got in!" and tries to expel it with a sneeze. However, this crosstalk doesn't happen to everyone. Research suggests it is only seen in 25% of Japanese people and 18-35% of people worldwide.

Data: A 2019 study by the National Center of Neurology and Psychiatry found that neural hypersensitivity is involved. Source: genequest.jp

◇ Modern Times: The hidden impact on daily life

This photic sneeze reflex actually has surprising effects even today. For example, you might sneeze the moment you exit a highway tunnel, which could make driving dangerous. In the United States, there is even research recommending sunglasses for pilots to prevent them from sneezing due to sunlight. On X, the topic "Does anyone else sneeze from light?" has come up, with voices of empathy spreading, such as "My whole family is like that!" or "I'm not the only one!" Looking at posts from March 2025, there was even a survey where about 30% of people answered "Yes." Small daily realizations are connecting everyone's curiosity.

Data: Report from American Aerospace Medicine (FAA). Source: FAA

◇ Reflection: What if this reflex didn't exist?

The photic sneeze reflex might not just be an interesting phenomenon. Long ago, when humans lived outdoors, it might have been a "defensive reaction" to expel dust or insects from the nose by sneezing in response to light. It may not be very useful in modern times, but it could be a remnant of evolution. What if this reflex didn't exist? For example, people working in factories during the Industrial Revolution might have suffered more from nasal congestion. It is surprising that a daily "Achoo!" is actually connected to history and science.