The photic sneeze reflex, also known as the backronym ACHOO syndrome (Autosomal Dominant Compelling Helio-Ophthalmic Outburst), is a phenomenon where exposure to bright light, typically sunlight, induces sneezing in specific individuals.
This reflex is an involuntary response and is not fully understood, but it is believed to be a genetic trait that affects some people. The exact cause of the photic sneeze reflex is not well-documented. Still, it is thought to involve a crossover of signals in the brain between the optic nerve and the trigeminal nerve, which controls facial sensations and reflexes.
A survey conducted by the School of Optometry at the University of Alabama at Birmingham found that 67% of respondents who identified as photic sneezers were female and 94% were Caucasian. The study also found that photic sneezing was significantly more common in people with a deviated nasal septum.
When a person with this reflex is exposed to bright light, it may trigger an abnormal response in the trigeminal nerve, leading to a sneeze. I know that if I’m going to sneeze, but it is starting to go away, looking directly into a light fixture at work will usually go ahead and complete the sneeze.
The photic sneeze reflex is believed to be an inherited trait, typically following an autosomal dominant inheritance pattern[1], where a single copy of the gene is sufficient to express the trait. Bright sunlight is the most common trigger, but other intense light sources, such as camera flashes or bright indoor lights, can also induce sneezing in affected individuals.
A condition called gustatory rhinitis can cause some individuals to sneeze after eating, particularly after the consumption of spicy foods. Stomach fullness is another example of a stimulus that can cause uncontrollable sneezing. Those who exhibit this symptom or disorder, called snatiation, undergo uncontrollable fits of 3–15 sneezes immediately after eating large meals that completely fill the stomach, regardless of the type of food eaten. Snatiation is not believed to be an allergic reaction of any kind.
The prevalence of the photic sneeze reflex varies among populations. It is estimated that between 18% and 35% of the population may experience this reflex. Some individuals may experience multiple consecutive sneezes when exposed to bright light, while others may only sneeze once. The exact mechanism of the photic sneeze reflex is still under investigation.
Still, it is thought to involve the miswiring or cross-activation of neural pathways in response to light stimulation. It’s important to note that the photic sneeze reflex is generally considered harmless and not a cause for concern.
When the trigeminal nerve[2] is directly stimulated, there is the possibility that increased light sensitivity in the ocular nerve could result. An example of directly stimulating would be plucking an eyebrow or pulling hair. In many people who show the photic sneeze reflex, even this direct stimulation can lead to a photic sneeze which is why we find it easier to sneeze while looking at a bright light.
However, individuals who experience excessive or uncontrollable sneezing triggered by light should consult with a medical professional for evaluation and potential management strategies.
Footnotes
- The autosomal dominant inheritance pattern is a mode of genetic inheritance where the presence of a single copy of a mutated gene on one of the autosomal chromosomes (non-sex chromosomes) is sufficient to cause the expression of a specific trait or disorder. In this pattern, an affected individual typically has one affected parent, and there is a 50% chance of passing the mutated gene to each offspring. Autosomal dominant disorders include conditions such as Huntington’s disease and Marfan syndrome. This inheritance pattern can be contrasted with autosomal recessive inheritance, where two copies of the mutated gene (one from each parent) are required for the trait or disorder to be expressed. Understanding inheritance patterns is crucial in genetics and has implications for risk assessment, genetic counseling, and the study of inherited diseases. [Back]
- The trigeminal nerve, also known as cranial nerve V, is one of the twelve cranial nerves originating from the brainstem. It is the largest of the cranial nerves and plays a critical role in sensory perception and motor function of the face. The trigeminal nerve has three main branches: the ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions, which innervate different areas of the face and head. It is responsible for transmitting sensations of touch, temperature, and pain from the face to the brain, as well as controlling the muscles used for chewing. Dysfunction of the trigeminal nerve can lead to various neurological conditions, including trigeminal neuralgia, which is characterized by severe facial pain. Proper functioning of the trigeminal nerve is essential for everyday activities such as eating, speaking, and facial expressions. [Back]
Further Reading
Sources
- “Photic sneeze reflex: another variant of the trigeminocardiac reflex?” (Oct 10, 2019) https://www.futuremedicine.com/doi/10.2217/fnl-2019-0007
- “Photic sneeze reflex” (updated July 17, 2023) https://en.wikipedia.org/wiki/Photic_sneeze_reflex
- “Why does bright light cause some people to sneeze?” (November 18, 2002) https://www.scientificamerican.com/article/why-does-bright-light-cau/
- “Guide To Photic Sneeze Reflex, ACHOO Syndrome And Sun Sneeze” https://atlasbiomed.com/blog/photic-sneeze-reflex/
