Why does looking at bright light trigger sneezing in some people?

Why does looking at bright light trigger sneezing in some people?

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Why does looking at bright light trigger sneezing in some people?

Are there any recent studies that have found a cause for this Photic sneeze reflex? The Wikipedia article only references studies pertaining to the effect, stating that the cause is unknown. The article also states that "the condition affects 18-35% of the population", which seems to be quite a large percentage.

What could have lead to the development and persistence of such a genetic trait in humans? Are there any evolutionary advantages to this?

You are talking about the photic sneeze reflex.

The mechanisms are not entirely understood, but it affects 18-35% of the population.

According to Wikipedia (although this passage is not sourced):

The probable cause is a congenital malfunction in nerve signals in the trigeminal nerve nuclei. The fifth cranial nerve, called the trigeminal nerve, is apparently responsible for sneezes. Research suggests that some people have an association between this nerve and the nerve that transmits visual impulses to the brain. Overstimulation of the optic nerve triggers the trigeminal nerve, and this causes the photic sneeze reflex.

And, it could be advantageous:

On the other hand, some people with the trait feel that it is advantageous. In the event that nasal discomfort occurs, but to an extent that is insufficient to induce a sneeze, intentionally seeking and finding a light source facilitates the sneezing process and is in turn a mode of relief.

Also, anecdotally, as I too photosneeze, I can see an advantage: should the atmosphere become weaker in the future, and allow more light to enter than we are accustomed to, it would discourage looking directly at the sun.

In high school biology, we had to read a book called "Survival of the Sickest". In this book, the idea is presented that this reflex evolved during humankind's "caveman" days. The author presented the anthropological induction that after spending periods of time in a dark, dank cave, mold spores begin to accumulate on the human body and inside immediate and open orifices. The nose, being moist, open, and pulling air in, would then be prime nesting ground for mold. Some claim, then, that humans evolved this reflex as a way of clearing the nose of mold and other impurities upon exiting a cave and entering the brightly lit outside world.

Here's Why The Sun Makes Some People Sneeze, According to Science

While certainly not as dramatic as bursting into flames, for some people, sudden exposure to sunlight produces an unexpected reflex - they sneeze. Chances are this happens to you, or one of your friends. It's called the 'photic sneeze reflex' and is more common than you'd expect, occurring in 17 to 35 percent of the world's population, according to informal surveys. But what causes it?

Sneezing can't really be controlled - it's one of the body's reflexes, and is typically associated with irritation in the nose. From here the signal is sent via neural pathways to the brain, resulting in a powerful release of air through your mouth and nose, which not only helps expel mucous or irritants from the nasal passages as fast as possible, but also contracts a bunch of muscles in the body, including the eyelids and the trachea.

When it comes to sun sneezing, even Greek philosopher Aristotle famously noticed the phenomenon and mentioned it in the 'Nose' chapter of his Book of Problems: "Why does the heat of the Sun provoke sneezing, and not the heat of the fire?"

However, the photic sneeze reflex has nothing to do with heat, and instead appears to be the result of crossed wires somewhere along the trigeminal nerve. Also known as the fifth cranial nerve, it's the largest and most complex paired nerve in the head, with three major branches leading to the eyes, nasal cavity, and the jaw. It's a crowded place in terms of nervous signalling, so it's not surprising that the trigeminal nerve would occasionally get the reflexes wrong. Bright light causes your pupils to contract, so that signal might be mistakenly sent to the nose as well.

Another nervous system-related hypothesis states that these Sun-related sneezes might occur thanks to 'parasympathetic generalisation': a process that occurs when one part of the parasympathetic nervous system - such as the pupil of the eye - is excited by a stimulus and happens to activate other parts of the system as well - such as the membranes in the nose.

Whichever nervous system misfire is the exact cause of the problem, researchers have figured out the underlying genetics of sun-sneezing. "[T]he reflex is now also known by the hilariously apt acronym Achoo, which stands for Autosomal Dominant Compelling Helio-opthalmic Outburst," writes Jason Goldman at BBC. "'Autosomal' because the affiliated gene is located on one of the non-sex-linked chromosomes, and 'dominant' because you only need to inherit it from one of your parents to express the trait."

Even though commonly associated with the Sun, photic sneeze reflex can also happen thanks to any other sudden light exposure, such as a flashlight in a dark room. And because it's a harmless condition, you can go on and try this on your sneeze-afflicted friend - just don't tell them it was our idea.

Why do I sneeze sometimes when I look at the sun?

When I look at the sun on a bright day it sometimes makes me sneeze. Why is this?

You have asked one of my all-time favourite bits of biology trivia and I am delighted to have got here first to answer it. However, the answer is rather complicted, so bear with me!

First off, your sneeze is what we call a 'reflex' action. It is an action that you cannot control (you can't make yourself sneeze, like you can stick your tongue out). When your nose is stimulated by something that irritates it (like pepper) the nerves send a message to the brain where the sneeze reflex set of nerves send a message to your lungs to make you sneeze and flush out the nose.

When nerve cells are stimulated they pass on a chemical and electrical message to the next nerve cell in the chain. However, if it is a very strong message, this might also leak out and stimulate nearby nerve cells. You can probably now see where this is going.

So, when you look at the sun or a bright light, your eyes (and their nerves) suddenly have lots of very strong information to pass to the brain. So in addition to passing on their message, they also 'leak' a bit. Part of the path for the optice nerves (from your eyes) happens to be close to your sneeze reflex and so it can be triggered by accident.

So, when you look at the sun, you eyes accidently trigger a sneeze. I hope that's clear for you.

Last edited by David Hone (16th Feb 2007 14:27:18 )

This happens to me too, but the worst time for me is an overcast but dry day. I have to wear sunglasses while driving or I'm sneezing so much I worry I might crash.

Apparently it's also a test for pilots in some military branches. They don't want people who can be severly incapacitated for a few seconds by something as mundane as the sun.

I'm going to play devil's advocate and say I don't believe that for an instant! The idea that the trigeminal nerve which controls the motor aspects of a sneeze is "close" to the optic nerve and thus somehow the bright light stimulation of the optic "spills over" to the trigeminal is to my mind just not tenable from a neurophysiological or neuroanatomical point of view! The trigeminal nerve is equally close to many other cranial nerves yet the response we are talking about is very specific. I think it would be better to say this is an intersting phenomenon that is under-researched and the cause is unknown. What IS of interest is that it is clearly genetic - only about 25% of people exhibit this phenomenon.

I have to say, I'm with David on this one. I used to believe it, but after a brief but informative neuroscience module in second year, I'm not so sure.

What about people half way though. I find that I can look at bright lights fine, unless I'm half about to sneeze and then looking at one will set the sneeze off! (Which can be quite useful. ) but that seems to be half way between what you're talking about and no reaction at all.

I'm also an occasional photic sneezer but I've never observed it happening in my children (which doesn't mean it has never happened!). I think there were some studies awhile ago that strongly suggested that a predisposition to photic sneezing is genetic, as David says. It will be interesting to see if the 'condition' is non-homogeneous, e.g., if there are adult-onset forms. I agree with David about the trigeminal* and I think there are some studies that have shown that the sneezing is still present in blind-folded people. Recent studies (e.g., suggest that visual cues are important!

* that is assuming the condition is not caused by a neuroanatomical change that brings trigeminal and optic nerve processing into close(r) functional proximity!

Last edited by Steve Lolait (26th Jul 2011 14:05:48 )

Like Adam, I'm personally at the halfway house of photic sneezing. But more importantly, I was taught that the maxillary branch of the trigeminal nerve (cranial nerve 5, part 2) is responsible for the nasal mucosal sensory input to the brain. This nerve branch is also sensory for the surface of the upper cheeks and for the skin over your nose.

Thus, when much sunlight tickles this area, in some people it may trigger the sneeze reflex, just as pepper does when inside the nose - simply because the sensory input is the same for both regions. This makes sense because photic sneezers often still sneeze when their eyes are closed - its the light on their face that may create a response. I heard that large or sudden changes in light intensity may trigger the reflex, but as David says, I'm sure there's much more to discover about this unusual trait.

Last edited by Nick Hayward (26th Jul 2011 17:39:55 )

I'm sure this is no help, but I was told years ago that sneezing in bright sunlight was because photons get up your nose.

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For example, in 2010, a Swiss study found greater stimulation of the primary and secondary visual cortex — regions of the brain that processes visual information — of 10 photic sneezers when exposed to various wavelengths of light compared to those who do not have the reflex. The optic nerve feeds information to the visual cortex.

In contrast, Spanish researchers in 2016 found individuals with photic sneeze reflex had thickened nerves in the eye’s cornea. Those nerves exit the eye via the trigeminal nerve. In that study, however, the 13 individuals analyzed were all from the same family.

Taking a closer look at photic sneeze reflex could reveal important insights on other diseases. Photo by Athit Perawongmetha/Reuters

Ptáček studies the genetics behind episodic disorders like migraine headaches and epilepsy. His lab has collected surveys on photic sneeze reflex for years but has lacked funding to analyze the information in depth. He believes a dearth of money is to blame for few exhaustive studies.

“It’s hard to get funding because reviewers don’t think of it as a problem,” he said. “Instead, money goes to research on diseases like Parkinson’s and multiple sclerosis.”

In most cases, sneezes summoned by sudden changes in light are relatively harmless. But the triple threat of bright light-induced temporary blindness, an induced sneeze and subsequent eyelid closure could be threatening under special circumstances. Case studies suggest high-wire acrobats, baseball outfielders and combat pilots may be adversely impacted. From personal experience, I can attest that sneezing after driving out of a dark tunnel at 60 miles an hour can be — at least temporarily — frightening.

Ptáček thinks taking a closer look at photic sneeze reflex could reveal important insights on other diseases.

“If we knew one or more genes that cause photic sneeze reflex, I don’t doubt that that might teach us fundamental things about reflex disorders like epilepsy,” he said. “Some of the most important advancements in medicine come from not being focused on medicine at all.”

Left: Photic sneeze reflex spurs light-induced sneezes in 10 to 30 percent of people. Photo by Peter Widmann/Getty Images

Looking at the Sun Can Trigger a Sneeze

Have you ever emerged from a matinee movie, squinted into the sudden burst of sunlight and sneezed uncontrollably? Up to a third of the population will answer this question with an emphatic "Yes!" (whereas nearly everyone else scratches their head in confusion). Sneezing as the result of being exposed to a bright light&mdashknown as the photic sneeze reflex&mdashis a genetic quirk that is still unexplained by science, even though it has intrigued some of history's greatest minds.

Aristotle mused about why one sneezes more after looking at the sun in The Book of Problems: "Why does the heat of the sun provoke sneezing?" He surmised that the heat of the sun on the nose was probably responsible.

Some 2 ,000 years later, in the early 17th century, English philosopher Francis Bacon neatly refuted that idea by stepping into the sun with his eyes closed&mdashthe heat was still there, but the sneeze was not (a compact demonstration of the fledgling scientific method). Bacon's best guess was that the sun's light made the eyes water, and then that moisture ("braine humour," literally) seeped into and irritated the nose.

Humours aside, Bacon's moisture hypothesis seemed quite reasonable until our modern understanding of physiology made it clear that the sneeze happens too quickly after light exposure to be the result of the comparatively sluggish tear ducts. So neurology steps in: Most experts now agree that crossed wires in the brain are probably responsible for the photic sneeze reflex.

A sneeze is usually triggered by an irritation in the nose, which is sensed by the trigeminal nerve, a cranial nerve responsible for facial sensation and motor control. This nerve is in close proximity to the optic nerve, which senses, for example, a sudden flood of light entering the retina. As the optic nerve fires to signal the brain to constrict the pupils, the theory goes, some of the electrical signal is sensed by the trigeminal nerve and mistaken by the brain as an irritant in the nose. Hence, a sneeze.

But because this harmless (albeit potentially embarrassing) phenomenon doesn't seem to be linked with any other medical condition, scientific study of the subject has been scarce. Research has done little more than document its existence and attempt to gauge its prevalence. No rigorous studies exist, but informal surveys peg 10 to 35 percent of the population as photic sneezers. A study in the 1960s showed that the trait is autosomal-dominant&mdashthe gene is neither on the X nor Y chromosome and only one copy of the gene has to be present for the trait to be expressed&mdashso if one parent sneezes when they look at a bright light, about half of his or her children will, too.

The genetic culprit remains unidentified, but scientists are starting to take an interest in trying to find out. "I think it's worth doing," says Louis Ptácek, a neurologist at the University of California, San Francisco, and an investigator at the Howard Hughes Medical Institute. Ptácek studies episodic disorders such as epilepsy and migraine headaches, and he believes that investigating the photic sneeze reflex could shed light on their related neurology.

Epileptic seizures are sometimes triggered by flashing lights and migraine headaches are often accompanied by photophobia. "If we could find a gene that causes photic sneezing, we could study that gene and we might learn something about the visual pathway and some of these other reflex phenomena," Ptácek says.

But until he and his colleagues find the right families for their study, the photic sneeze reflex will remain something of a genetic novelty act, like the ability to roll your tongue. Although a 1993 paper in the journal Military Medicine raised concerns that light-induced sneezing might endanger fighter pilots, for whom a split second of lost vision could be lethal in certain situations, such fear was largely put to rest when a small study found that wearing sunglasses eliminated the effect.

Beyond that blip of gravitas, papers published about photic sneezing have largely leaned toward the whimsical end of the spectrum. Consider one 1978 publication that took advantage of the then-raging acronym fad and suggested an alternate name for the photic sneeze reflex: Autosomal-dominant Compelling Helio-Ophthalmic Outburst syndrome, or, of course, ACHOO.


Kate Schrock has been an editor of Scientific American MIND since 2007, where she edits feature articles and runs Head Lines, the magazine's news department. After studying astronomy and physics at the University of Southern California, she worked in the Laboratory of Neuro Imaging at the University of California, Los Angeles, studying the brain structure of people with schizophrenia. She then enrolled in the Science, Health and Environmental Reporting program at New York University, where she earned a master's degree in journalism.

Why do some people sneeze when they look at the sun?

Have you ever stepped out of a dim subway station into the sunshine and felt that telltale tickle in your nose—the unmistakable need to sneeze? Sneezing in the sudden presence of bright light, especially sunlight, is a phenomenon known as sun sneezing or the photic sneeze reflex. It affects anywhere between 10 to 35 percent of the population, depending on which survey you read. A 1987 study in the Cleveland Clinic Journal of Medicine, for example, estimated its prevalence at 17 to 35 percent of the population. A 1983 study in Human Heredity found a 24 percent prevalence among 460 blood donors.

Although most of us aren’t sun sneezers, it’s a common enough curiosity to get lots of people wondering: What’s going on here?

There’s still no hard evidence to fully explain sun sneezing, but scientific and popular attention has largely focused on a particular hypothesis proposed in 1964 by Henry Everett when he was a psychiatrist at Johns Hopkins University Hospital. According to the hypothesis, the photic sneeze reflex is caused by a confusion of nerve signals in pathways very near one another. Since sneezing is such a sudden and involuntary reflex, the cause is probably located in the nervous system, which is capable of transmitting signals very quickly.

Researchers suspect that two important reflexes may play a key role in sun sneezing. The first is the pupillary light reflex. In this reflex, bright light entering the eyes sends signals along the optic nerve to the brain, which sends signals back to the eyes to constrict the pupils—a means of adjusting to differently lit environments. The second is the sneeze reflex, in which a cranial nerve called the trigeminal nerve detects a tickling in the nose and alerts the brain, which in turn stimulates the chest, nose, mouth and other muscles involved in sneezing.

For most of us, the pathways involved in these two reflexes—though physically close—do not directly interact. But in sun sneezers, the hypothesis claims, one pathway stimulates the other. The result? Exposure to bright light sends a signal to the brain to constrict the pupils, as usual, but the crossed wires rouse a sneeze as well. “While this is an interesting hypothesis, there’s no data supporting it or any other hypothesis for that matter,” said Louis Ptácek via email. Ptácek is a neurologist at the University of California, San Francisco who studies the photic sneeze reflex.

An alternative hypothesis attempts to explain sun sneezing and other strange sneezing behaviors by singling out the medulla oblongata, a part of the brainstem that helps regulate many involuntary processes, including breathing, heart rate and sneezing. Believe it or not, some people always sneeze after eating a large meal—a condition called snatiation—while others sneeze during orgasm. Constriction of the pupils, the feeling of being stuffed, and orgasm are exactly the kind of reflexes mediated by the medulla. The implication is that, for some individuals, all these signals flowing to the same area of the brainstem might be getting a bit mixed up.

The specific genes responsible for sun sneezing have not yet been identified, but scientists can guess your chances of having the photic sneeze reflex because of the way it’s inherited—it’s an autosomal dominant trait. This means that if just one of your parents has one copy of the culprit gene, you have a 50 percent chance of being a sun sneezer. In 1978, a group of witty eggheads pounced on the new genetic evidence as an opportunity to create the following acronym for the photic sneeze reflex: Autosomal-dominant Compelling Helio-Ophthalmic Outburst syndrome—ACHOO!

Although most sun sneezers accept their condition as an odd but harmless quirk, there’s been plenty of speculation about harmful consequences. According to a 1993 issue of Military Medicine, sun sneezing could threaten combat pilots by interfering with their vision, leading to potentially fatal situations. Similar fears have been raised about drivers emerging from dark tunnels into bright light. Some researchers have even expressed concerns over baseball players searching the sunny skies for a fly ball.

So much for the gloom and doom. Are there any benefits to the photic sneeze reflex—anything at all? Some have theorized that sun sneezing is a gift of evolution, passed down from our cavemen forefathers. According to the theory, after hanging out in dark, dirty caves all day, our ancestors’ noses and throats would become full of dust and need a little forceful cleaning. When the cavemen emerged from their dwellings into the sun, they would sneeze, thereby clearing their noses and throats of cave must. Unfortunately, this theory is an old wives’ tale, about as verifiable as the Area 51 conspiracy.

The photic sneeze reflex has largely eluded our attempts to understand it, remaining a mystery for neuroscientists and sun sneezers alike. “There is so little known about the photic sneeze reflex that I think the jury is completely out at this point,” said Ptácek.

Sun sneezing is, however, becoming more well known. The photic sneeze reflex recently attracted the attention of 23andMe, a company that will analyze the DNA in your saliva to predict your chances of having certain heritable traits and diseases. Sun sneezing also found its way into the popular Berenstain Bears series of children’s books. And anecdotal evidence suggests that some people take advantage of the reflex, training themselves to hasten an imminent sneeze by directing their attention to the sun. There’s even an online support group for those with the photic sneeze reflex.

If you would like to help scientists specify the genetic factors involved in sun sneezing, you can apply to participate in ongoing research at the University of California, San Francisco, where Ptácek and his colleagues work. “We’ve collected some interesting families,” Ptácek said, but they will need many more volunteers before they find something conclusive.

Sun sneezing origins

Sun sneezing has been documented for many centuries. In fact, the Greek philosopher Aristotle was one of the first to explore its occurrence in 350 BCE and hypothesized that the sun warmed the inside of the nose, generating a sneeze.

English philosopher Francis Bacon disproved this theory in the 17th century by noting that facing the sun with closed eyes did not elicit a sneeze response. “Bacon thought that the eyes may actually play an important role in photic sneeze reflex instead,” Dr. Bleier said.

In recent studies, it’s been shown that the reflex seems to be caused by a change in light intensity rather than by a specific type of light. This is why bright lights, camera flashes and even the brightness from snow can sometimes cause a sneezing sensation.

Still, the exact mechanism of the photic sneeze reflex is not clear. The most common explanation can be traced to Dr. Henry Everett who, in 1964, proposed that the effect resulted from a confusion of nerve signals in the brain.

“When your eyes are exposed to bright light, the parasympathetic nervous system, or the rest and digest response, causes the pupils to constrict to protect the eyes from light damage,” said Dr. Bleier. “This effect may indirectly activate other parts of your rest and digest response, including those that control mucus secretion and the sneeze response in your nose.”

Sneezing uncontrollably after sex may be more common than realised

Thinking about sex or experiencing an orgasm sends some people into an uncontrolled bout of sneezing, and according to two researchers the problem may be more common than the medical profession had realised.

The doctors who investigated the link are not yet sure why sex and sneezing are linked in some people, but they suspect it is due to a faulty connection in the autonomic nervous system – the system that exercises unconscious control of, among other things, heart rate, digestion and pupil dilation.

Dr Harold Maxwell, a consultant psychiatrist at West Middlesex University Hospital in London, was first alerted to the condition when a middle-aged male patient described uncontrollable fits of sneezing whenever he thought about sex. When Maxwell and his colleague Mahmood Bhutta, a surgeon at Wexham Park Hospital near Slough set out to investigate how common the problem is they could find only one similar case in the medical literature – a case reported in 1972 of a 69-year-old man who suffered severe sneezing after orgasm. "It may also be seen as embarrassing and people perhaps don't want to talk about it," said Bhutta.

To get some indication of how common the problem is he searched internet chatrooms for people discussing the issue. This highly unscientific survey identified 17 men and women who reported sneezing immediately after having sexual thoughts and three people who sneezed after orgasm. In four of the chatroom threads, respondents also said they had suffered the same problems, but in no case did people say they sneezed not only after sexual thoughts but also after orgasm. Bhutta believes the seemingly bizarre phenomenon may be more common than doctors had previously thought.

There are other examples of unrelated events triggering sneezing. According to a large Swedish study, 25% of people sneeze in response to bright light. Bhutta said that people who have the condition simply don't see it as unusual. "They think that everybody does that," he said. Much rarer are people who sneeze after a meal when they have a full stomach. This has been identified by scientists in just two families. "Possibly that is much more common that we think as well," said Bhutta.

Both phenomena are genetically inherited.

Sneezing and sex may be linked by a faulty connection in the autonomic nervous system that controls both the sneeze reflex and sexual responses. A similar mechanism is thought to underlie the observation that in some people massaging an eyeball can dramatically slow their heart rate.

"Further investigation in this field may help us to understand the sneeze reflex in more depth, and also allow us to give explanation and reassurance to the possibly significant number of people affected by this curious phenomenon," Bhutta and Maxwell wrote in the Journal of the Royal Society of Medicine.

How the Human Blockhead Works

When you watch someone perform the human blockhead trick, you probably wonder if he is in any pain. After all, a nail is sharp, and the inside of the nose is sensitive. Putting a foreign object deep into your nasal cavity isn't particularly comfortable, and it can be certainly painful when the performer is learning to do the trick. However, another obstacle -- sneezing -- can be harder to overcome.

Sneezing is a largely reflexive act that usually occurs when something irritates your nasal passageways. As with all reflexes, sneezing involves a reflex arc consisting of a receptor, a sensory nerve, an integration center, a motor nerve and an effector. Here's what happens:

  • The receptors, which are nerve endings in your nasal passageways, detect an irritant. This irritant might be an unusual smell, dust, animal dander, pepper, viruses that attack the mucous membranes or a variety of other substances.
  • Nerves carry these impulses to the sneezing center in your brain stem.
  • The sneezing center sends its instructions along your facial nerve and the nerves that lead to your lungs and diaphragm.
  • Your eyes start to water, and your nasal passageways secrete fluid. Your diaphragm moves abruptly, causing you to take a deep breath. Then, it and the muscles in your chest contract, causing the air to leave your nose and mouth suddenly and rapidly.

It's possible to put off sneezing, ignoring the tickling sensation in your nose. If the sensation passes, you can get away without sneezing. This isn't always possible, though -- sometimes, you simply have to sneeze.

On top of ruining the effect, sneezing while attempting to put a nail into the nasal cavity could be very dangerous. The sharp intake of air before the sneeze could potentially pull the foreign object further into the nasal passageway than the performer intends. The sudden movement of the head could also cause sharp objects to scrape against the interior of the passage. So when learning to perform the human blockhead act, people have to learn to ignore their sneeze reflex. Much like in sword swallowing, this can take a lot of practice.

The sneeze reflex is one of your body's defense mechanisms against bacteria and viruses-- when you sneeze, you forcibly expel particles that could make you sick. In other words, a human blockhead ignores one of the tools the body uses to prevent illness. In addition, the trick requires a person to place a foreign object in very close proximity to his sinuses and throat. This can potentially lead to illnesses, particularly sinus and throat infections. This is especially true when performers work in crowded conditions, like fairs and festivals. The foreign object is also a physical hazard, which has the potential to damage the tissues inside the nose and nasal cavity.

As with sword swallowing, performers who try the human blockhead put themselves at risk in pursuit of entertainment. It's not an activity that you should try at home or without the help of an experienced performer.

To learn more about the human blockhead and related acts, check out the links below.

Some people sneeze when they look at bright light or when they walk from a relatively dark room into bright sunlight. This behavior is known as the photic sneeze reflex, and researchers aren't exactly sure what causes it.

ELI5: Why is it that when someone needs to sneeze but can’t quite get it out, looking at a bright light helps?

The trigeminal nerve (triggers a sneeze) runs close to the optic nerve. Flooding the optic nerve suddenly (with light) can cause the trigeminal nerve to trigger.

Bonus tip: If it doesn't work the first time, look down and away, then back at the light. I almost never "lose" a sneeze anymore.

It’s the photic sneeze effect. A large percentage of people have a gene that causes them to sneeze when they look at the sun.

I prefer the term ACHOO syndrome. Photic sneeze reflex seems so bland.

It's really annoying too. I walk outside and sneeze 100% of the time during the day.

There's a nerve that runs from your nose to your brain called the trigeminal nerve. That nerve is located near the optic nerve. When that nerve gets tickled, you sneeze. That nerve is generally tickled by detecting stuff in your nose.

A decent portion of the population is born with a birth defect that causes the protective sheath of the trigeminal nerve to be weakened. That weakened sheath can allow the trigeminal nerve to be tickled by a strong enough signal being transmitted by the nearby optic nerve.

When you look at a sudden bright light, the optic nerve transmits a strong signal to the brain. This signal is strong enough that it can tickle the trigeminal nerve through its weakened sheath. And you sneeze.

Imagine two wires next to each other, and one of them has a bunch of holes in the plastic coating. Sometimes when you turn on one lamp, the other might flash on for a moment.

Watch the video: Γιατί ερωτεύεσαι ανθρώπους που ΔΕΝ είναι διαθέσιμοι; (May 2022).