What is the photic sneeze reflex (ACHOO syndrome)?
Sneezing is like coughing — it happens when your body is trying to get rid of something irritating or infectious. Sometimes, something else can trigger the sneeze reflex. When you sneeze from looking at the sun or another light, it’s called the photic sneeze reflex.
There are several other names for the photic sneeze reflex, including:
- Sun sneezing
- Photosneezia
- Autosomal dominant compelling helio-ophthalmic outburst (ACHOO) syndrome
Both natural light (from the sun) and artificial light (from electricity) can cause sneezing.
Causes of photic sneeze reflex
What causes the photic sneeze reflex isn’t known for sure. The condition itself is a genetic disorder, meaning it’s inherited. But the pathophysiology, or how your body responds to a disease and how it progresses, is unclear. The processes that lead to sneezing in response to bright light are complex.
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Genetic factors
ACHOO syndrome is autosomal dominant. This means you only have to inherit the gene from one parent to get ACHOO syndrome. If a parent does have it, you have a 50% chance of inheriting it.
The specific genetic variation that leads to ACHOO syndrome isn’t known, but it’s possible that it involves more than one change or gene. It’s relatively common, with around 18% to 35% of people estimated to have it. The sex distribution is not fully established — some studies have reported a higher prevalence in females, while others have found a slightly higher male prevalence. Photic sneeze has been suggested to be more common in people who smoke and people with a deviated septum. People with photic sneeze may be more likely to suffer from migraine than those without it.
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Neurological pathways
The sneeze reflex is normal but complex. It involves several different regions of the brain, different nerves and other parts of the central nervous system. How photic sneezing happens isn’t clear for sure, but it’s thought to involve optic-trigeminal summation. This refers to communication between the optic nerve and trigeminal nerve.
The optic nerve, located in the back of the eye, carries signals from your eye to your brain. It’s one of a few cranial nerves that are connected to your brain as part of the central nervous system.
Your trigeminal nerve is another cranial nerve. It has three branches that spread across the face. It sends signals from the brain to the face, including the eyes and nose.
Stimulating the trigeminal nerve can cause sneezing. So, with optic-trigeminal summation, it’s theorized that stimulating the optic nerve (like sensing light) can also stimulate the trigeminal nerve. These signals then lead to sneezing. Basically, this means that the response to bright light happens in your nose, as well as your eyes.
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Risks and implications
Sneezing isn’t dangerous on its own, but it can be if it happens under certain circumstances. This is especially true for people who work in professions where they may be suddenly exposed to a bright light (like pilots or miners). Other situations could include:
- Driving (especially going from dark to light, like when leaving a tunnel)
- Operating heavy machinery
- During exams that involve bright lights (like a dental or eye exam)
Undergoing surgery might also be problematic for people with photic sneeze reflex. Aside from the lights, having your eye injected with an anesthetic — for example a periocular injection before eye surgery — could trigger a sneeze since the injection stimulates your trigeminal nerve. This is a recognized concern for surgeons performing procedures on people with ACHOO syndrome.
Management and treatment
While there isn’t a treatment for photic sneeze reflex, there are tricks you can use to manage its frequency and severity.
Lifestyle adjustments
Making exposure to sunlight less sudden and dramatic can help your body’s response to it. Sunglasses and hats are an easy way to do this. If you have a condition that causes frequent sneezing, like hay fever or allergies, staying on top of treating it can help the symptoms of photic sneezing.
A way to control sneezing is to place your finger between your nose and lips (like you’re pretending to have a mustache). Applying pressure in this area is called the transverse philtral pressure technique, and it can help stop sneezing.
Medical interventions
There is no medical treatment for the photic sneeze reflex. One study looked at the use of propofol, an anesthetic used for general sedation, to suppress the reflex during cataract surgery. Further research is needed.
Living with the photic sneeze reflex
The exact causes of photic sneezing aren’t known for sure. But it’s thought to happen because of complex brain processes, where the optic nerve sees light and accidentally stimulates the trigeminal nerve. These mixed signals then cause the sneeze reflex.
Like regular sneezing, the photic sneeze reflex is largely harmless. However, there are certain situations where sneezing may be dangerous. Trying to limit very sudden exposures to bright light can help. If you’re going in for a medical procedure, even just a routine dental or eye exam, let your doctor know you have ACHOO syndrome.
With appropriate lifestyle adjustments, ACHOO syndrome shouldn’t bother you any more than regular sneezing.
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