When a person steps out of a dark building into the bright sunlight, they may suddenly feel the urge to sneeze, a common occurrence that affects up to 1 in 3 people. But what causes this phenomenon? This reflex, known as the photic sneeze reflex, has been noted since at least the 4th century BC, when the ancient Greek philosopher and scientist Aristotle posed the question: "Why is a person more likely to sneeze after looking at the sun?"
According to the Cleveland Clinic, the condition known as "photic sneeze reflex" is a dominant genetic trait. This means that a person has a 50% chance of inheriting this light-induced reaction if one of their biological parents has it, as reported by Live Science. Dr. David Lang, head of the Allergy and Clinical Immunology Department at the Cleveland Clinic's Respiratory Institute, explained that photic sneezing usually occurs after exposure to bright light, like sunlight, and often when transitioning from darkness to light, such as when turning on lights in a dark room. He emphasized that this reflex is "not due to a specific wavelength of light, but rather a result of changes in light intensity."
The intensity of the photic sneeze reflex can vary from person to person. For some, photic sneezing occurs only occasionally and is not a constant reaction, while for others, bright lights can lead to uncontrollable sneezing several times in succession. The Cleveland Clinic indicated that scientists are still uncertain about what exactly causes photic sneezing. However, some suggest that one possibility is that bright light may stimulate the trigeminal nerve, whose branches spread across the face. Professor Lang noted that light stimulating the branch that leads to the eye may also end up stimulating the branch that leads to the nose.
In a study conducted in 2010, researchers at a genetic testing foundation in California identified two mutations linked to photic sneezing. A study in Alabama in 1995 found that photic sneezing may also be associated with a deviated septum. At the same time, a study conducted in Japan in 2019 discovered a potential link between this reflex and migraines.
Photic sneezing is generally benign, though it may increase the risk of accidents on highways, especially if a person is suddenly exposed to changes in light intensity. Dr. William Howland, the medical director of the Orion Clinical Research Center in Austin, stated that "the main way to deal with photic sneezing is to wear sunglasses when going outside," noting that taking antihistamines, typically used for allergies, does not affect this reflex. Furthermore, Professor Lang suggested another possible method to prevent photic sneezing: pressing on the philtrum, the groove located below the center of the nose, with one finger horizontally, as if one were drawing a mustache with their finger.
A study conducted in Australia in 2019 indicated that applying pressure in this way might either overcome the irritation that the trigeminal nerve experiences from bright light or interfere with the neural signals that trigger photic sneezing.
