Have you ever felt the sudden urge to sneeze when stepping into bright sunlight or looking at a lamp? This reaction is called the photic sneeze reflex. Although harmless, scientists have long studied its genetic, neurological, and physiological aspects.
Photic sneezing is not dangerous and does not need medication. Its scientific name is ACHOO syndrome (Autosomal Dominant Compelling Helio-Ophthalmic Outburst). Despite seeming odd, it affects many people and is a benign reflex.
The reflex happens when bright light stimulates the trigeminal nerve, which controls facial sensations and motor functions, including sneezing. This nerve has three branches: ophthalmic, maxillary, and mandibular. In the photic sneeze reflex, the ophthalmic branch, which carries signals from the eyes and forehead, may be activated by the optic nerve when it reacts to sudden light. This cross-activation triggers an involuntary sneeze.
Photic sneeze reflex is largely genetic, inherited in an autosomal dominant pattern. Only one copy of the gene is needed to express it. Studies estimate that 18%–35% of people show this reflex. It often runs in families, though scientists have not yet identified the exact gene.
Sneezing is a complex process. When the trigeminal nerve receives a signal, it sends instructions to the brainstem’s sneeze center. The center coordinates actions like closing the eyes, taking a deep breath, and forcefully expelling air through the nose and mouth. In people with photic sneeze reflex, bright light can overstimulate the optic nerve, which lies near the trigeminal pathways, activating the reflex unexpectedly.
Humans have observed this reflex for centuries. Ancient Greek philosopher Aristotle noted that looking at the sun could induce sneezing. Over time, science replaced mystical explanations with studies of nerve stimulation and neurological pathways.
Modern research offers two main explanations. First, the reflex may result from parasympathetic overactivation, causing exaggerated sneezing when light hits the eyes. Second, it may be a vestigial reflex from early humans. Sneezing when moving from dark caves into sunlight could have helped clear dust and allergens.
For most people, the photic sneeze reflex is harmless. However, sneezing while driving or performing other tasks may cause minor risks. Wearing sunglasses or a wide-brimmed hat can reduce light exposure and the chance of sneezing. Awareness of this reflex also helps people prepare for sudden sneezes in bright environments.
The photic sneeze reflex shows how our sensory systems and reflexes interact. While scientists do not fully understand all mechanisms, it highlights the complexity of human biology and how genetics and neurological pathways influence everyday experiences.
