Did you walk out of a dark movie theater on a sunny day and suddenly start sneezing? If yes, you are not alone. A surprisingly large number of people have this strange reflex response to a sudden increase in light intensity.

How common is this problem

It is actually a medically recognized condition known as the photic sneeze reflex, or photic sneeze reflex. It affects up to 33 percent of the population in the US alone. 67 percent are female and 94% are of Caucasian ancestry, according to a 1995 study by the University of Alabama at Birmingham. The data also suggests that this trait is partly genetic. So, what is it anyway?

This question perplexed even the ancient Greek philosopher Aristotle about 2300 years ago, when he put big question: Why does the sun cause sneezing?

Leading theory

True, there is not much solid scientific research on the topic, as the condition is often viewed as a humorous fad rather than a debilitating disease.
However, the leading theory is that instances of sneezing due to the sun may be caused by a minor trigeminal nerve glitch. It is one of the largest cranial nerves and carries sensory information to separate branches under the eyes, nose, mouth, and jaws. Abnormal sneezing is caused by stimulation of the trigeminal nerve in the lining of the nasal cavity.

People with a photic sneeze reflex may have subtle changes in the neural network in this area, causing unintended signals to cause a sneeze when it shouldn't. The theory says that bright light makes people close their eyes. This nerve signal inadvertently excites nerve pathways that irritate mucosal ducts a few centimeters away in the nose. The brain mistakenly perceives this as an irritant, which consequently leads to sneezing.

An evolutionary relic?

Some scientists have gone even further, as they suggest that such sneezing may be an evolutionary relic of our ancestors. When they lived in a musty and dusty cave, red-hot from fire and filled with smoke, sneezing when going outside could be beneficial, as it cleared the respiratory tract of pathogens and foreign bodies. However, this is pure speculation.

The harsh truth is still unknown. But after scientists find an eternal source of energy and cures for all known diseases, they may have time to solve this mystery as well.

A study shows that 35% of people experience a "light sneeze reflex". Getting from darkness to bright light, they sneeze. There is evidence that this predisposition is inherited.

The most convincing theory of the light sneeze reflex is that bright light, which irritates the optic nerve of each eye, somehow affects the receptors that play a role in the process of ordinary sneezing. The visual and olfactory receptors are located close to each other, like the optic and olfactory nerves. Indeed, these nerves enter the brain at almost the same point. In some people, after a long period of being in the dark, when exposed to bright light, the pupils do not contract, and the eyes become irritated. For unknown reasons, the optic and olfactory nerves "close", and the brain perceives the visual stimulus as olfactory, that is, sent by the nose, and not by the eyes. The brain stimulates the sneeze to get rid of the irritant, as if it were dust, dirt, pollen, or some other foreign substance. In addition to this, when bright light enters the eyes, due to severe visual stress, tears may appear. Tears flowing from the tear ducts can themselves cause sneezing, as happens when they are not provoked by bright light.

Initially, scientists deciphered the genome in order to find the cause of certain diseases (and therefore their prevention and treatment). But decades of conscientious study of human DNA has led to the fact that in personal account there are funny signs that prolong life, except that they cause laughter.

Smell of asparagus in urine

People are divided into two types: those who distinguish the strange smell of urine after eating asparagus, and those who do not. This feature has been noted for a long time, in early XVIII century, and put before scientists the question: what is the reason for this - with the inability to catch the smell, or with the inability of the body to process asparagus into such odorous substances.

To find out this question, scientists conducted a series of rather amusing, as it is easy to imagine, scientific experiments and made a discovery. It turned out that both hypotheses are correct, and the presence of strange odors in the urine after asparagus is a complex of hereditary traits. Odor discrimination depends both on the characteristics of asparagus acid metabolism and on the ability to distinguish the odor of the sulfur-containing compound methanethiol.

Type of earwax

It rarely occurs to genetic Europeans, but earwax is different. Liquid and sticky or hard and dry - also depends on the genes. If you have a jar of cotton swabs and deodorant in your bathroom, you most likely have a dominant variant of the ABCC11 gene.

And what about deodorant? It turns out that the type of earwax is also associated with sweating. And the owners of the recessive ABCC11 allele for dry earwax receive a gift of reduced sweating (which means fewer bacteria that cause an unpleasant odor). The majority of the Asian population are carriers of the recessive variant of the ABCC11 gene, so deodorants are much less popular in this region.

Sneeze in the light

Remember as a child, when your mother pulled the curtains in the morning, and light entered the room, you immediately sneezed? This is not at all because Soviet curtains are so dusty. It at you such polymorphism.

This habit is called the light sneeze reflex. This is due to the fact that bright light through the photoreceptors of the eye causes reflex irritation. nerve endings nasal mucosa and you sneeze. A 2010 study found that the trait is hereditary and occurs in 18-35% of people.
There is evidence that antihistamines reduce light sneezing.

Perfect Pitch

Having gained access to genetic research, scientists began to have fun and test everything in a row (especially "outstanding" abilities). Bringing together families of musicians perfect pitch and carried out genetic testing. Oddly enough, it turned out that there is a correlation between heredity and absolute pitch. And also between perfect hearing and the so-called synesthesia - the ability to "see" sounds and distinguish their colors. For example, before the first octave will be brown.

Fifty Shades of Gray

While outstanding musicians see the notes, some equally outstanding people do not see the colors of the blue spectrum. This rarest form of color blindness is also inherited in an autosomal dominant manner. People with the dominant allele of the OPN1SW gene will see the logo of the Atlas biomedical holding as follows:

For dessert - when you're craving salty

Love for pickles is not only a temporary insanity during pregnancy, but also a genetic trait. It is determined by the PKL3 gene, which codes for eight-stranded receptors responsible for detecting a salty taste as pleasant.
In general, there is nothing wrong with the “salty” version of this genetic trait. Just try to get into a jar of cucumbers in the morning and not on an empty stomach.

PS A very attentive reader will surely notice the set-up in this post - and will receive a delicious gift from the team. We will announce the winners in an update to the post in 24 hours.

Update

A heated discussion unfolded in the comments, as a result of the discussion, a set-up and several clarifications were found.
The majority turned out to be right: scientists have not yet been able to find any genetic craving for salt (unlike

The human tendency to sneeze at the sight of bright light was noted by the ancient Greek scientist Aristotle. In The Book of Problems, he (or probably his students) wondered, "Why does the heat from the sun make us sneeze, but the heat from a campfire doesn't?". He came to the conclusion that solar heat provokes the transition of nasal cavity fluids into an aerosol state, which activates the sneezing process. The heat from a campfire, on the other hand, evaporates these fluids, neutralizing the urge to sneeze. Of course, Aristotle mistakenly believed that heat, not light, makes us sneeze, but thanks to him we know that mankind was familiar with this phenomenon already in the 3rd century BC.
In the early 1950s, the French scientist Sedan conducted the first ever study of the unusual reflex. He noticed that some patients sneeze when he shines an ophthalmoscope, a device for examining the fundus, into their eyes. Sedan conducted several experiments and found a similar reaction of people to bright sunlight, camera flash and ultraviolet rays. Having discovered a new phenomenon for himself, Sedan could not, however, find a medical explanation for it.
The situation began to clear up a few years later, when in 1964 the physicist H.C. Everest published an article in the journal Neurology on the "light sneeze reflex." It was found that this reaction affects from 17 to 35% of the world's population.
Today we know much more about the causes behind the "light sneeze reflex". It is familiar to us as the "Apchi" process (analogous to the English onomatopoeia Achoo), denoting an autosomal dominant involuntary helio-ocular burst syndrome. “Autosomal” means that the gene is located on the non-sex chromosome, and “dominant” means that it is enough to inherit the syndrome from only one of the parents.
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In 2010, several genetic scientists led by Nicholas Erickson studied the genotypes of about 10,000 clients of the private biotechnology company 23andMe and identified two single nucleotide polymorphisms that were associated with sneezing in the sun. One of them allowed scientists to compare two seemingly unrelated syndromes, since it was located next to a gene that was directly related to the occurrence of epileptic seizures under the influence of light rays.
Despite the available data, no one can still unequivocally say exactly how optical stimulation of the eyes makes a person sneeze. One thing is known for sure: the eyes and nose are connected through the trigeminal nerve. Through this nerve, stimulation of one part of the body provokes a response in another part of it.

Have you ever stepped out into bright sunlight and suddenly started sneezing? Every third person will answer this question in the affirmative.

Sneezing as a result of exposure to bright light is commonly referred to as photic sneeze reflex.

This is a genetic feature that science cannot fully explain, although this phenomenon has worried many scientists for many years.

Aristotle discussed why some people sneeze more often when looking at the sun than others in his book The Book of Problems: "Why does the heat of the sun cause sneezing?" He believed that the reason is the effect of solar heat on the nose.

2,000 years later in the early 17th century English philosopher Francis Bacon proved this idea untenable by going out into the sunlight with his eyes closed—and never sneezing despite exposure to the sun's heat (a miniature demonstration of the then new scientific method). Bacon's most plausible explanation was that the sunlight causes the eyes to water, then the tears ("moisture of the brain", literally speaking) penetrate inside and irritate the nose.

Jokes aside, Bacon's moisture ingress hypothesis seemed to be quite acceptable until recently, when a new understanding of human physiology made it clear that sneezing occurs too quickly after being exposed to bright light to be the result of the comparatively slow passage of a tear through tear ducts.

So this is where neuroscience comes into play: most experts now agree that crossed wires in the brain are responsible for the sneeze reflex to light.

Normal sneezing is the result of nasal irritation, which is caused by the trigeminal nerve, a cranial nerve responsible for sensation and motor control of the face. This nerve is in close proximity to the optic nerve, which reacts, for example, to a sudden stream of light entering the retina.

When the optic nerve signals the brain to constrict pupils, the theory is that some electrical signals are picked up by the trigeminal nerve and misinterpreted by the brain as nasal irritation. As a result, we sneeze.

But since this harmless phenomenon does not appear to be associated with other medical conditions, Scientific research of this subject were few. Studies have given little more than a simple statement of the fact of the existence of this phenomenon and attempts to estimate its prevalence.

No rigorous studies have been conducted, but anecdotal observations have shown that between 10% and 35% of people suffer from a sneeze reflex to light.

A 1960 study showed it to be an autosomal dominant trait—i.e. the gene is located neither on the X nor on the Y chromosome, and that the existence of one copy of the gene is sufficient for the manifestation of this feature, i.e. if one parent sneezes looking at the sun, then half of his children will have the same feature.

Interesting observations

• Some people who have this feature find it useful.

When there is discomfort in the nose, but not enough to cause sneezing, you just need to quickly look for a source of bright light, or imagine it, for example, the light of the sun, and you will provoke a sneeze, which will bring relief.

• In the course of surgery in the eye or adjacent areas, the patient often requires an injection of local anesthesia into the eye. In patients suffering from light sneezing syndrome, the injection often causes reflex sneezing. Such patients should be pre-sedated. Otherwise, the patient begins to sneeze as soon as the needle comes into contact with the eye, and the doctor is forced to remove the needle immediately to avoid damaging the eye.
• The study showed that women are prone to this disorder in 67% of cases. Also 94% of them represented the European race.
• A full stomach is another stimulus that can trigger sneezing associated with the light sneeze reflex. People suffering from this disorder experience 3 to 15 sneezes immediately after eating a large amount of food.

The so-called sneeze reflex occurs regardless of the choice of food eaten and is not considered a type of allergy. Although this kind of sneezing reflex is even less studied than light sneezing as a response to periocular injection, it is considered to be an inherited feature of an autosomal dominant type.