The Curious Case of Sun Sneezing


Have you ever been in a dark place, say a movie theatre or a room with all the blinds close, and walked outside into the daylight when, all of a sudden, you begin to sneeze uncontrollably? You had no runny nose or desire to sneeze prior to this exposure to sunlight, but you just can’t help that big achoo? If you answered yes, then you are part of the twenty to thirty five percent of the human population that are “victims” of this not highly understood phenomenon, known as the “photic sneeze reflex” or a “solar sneeze.” Why do certain people have solar sneezes? How does it work? Only in the past few years have scientists begun to understand this rather odd trait.

The great Greek philosopher Aristotle in 350 BC asked the question in his first volume of The Book of Problems, “Why does the heat of the sun provoke sneezing?” This was the first recorded evidence of the photic sneeze reflex. Aristotle theorized that the heat of the sun caused moisture, sweating inside of the nose and mouth. In order to get rid of this moisture, one had to sneeze. Not a bad hypothesize.

In the 17th century, the great scientist and developer of the scientific method, Francis Bacon, tackled the question of solar sneezes. He proved that Aristotle theory was incorrect by looking at the sun with his eyes closed, which did not elicit the normal sneeze. Instead, he determined looking into the sun made one’s eyes water, which got into the nose and caused the sneeze. Said Bacon, “The drawing down the moisture of the brain; for it will make the eyes run with water; and the drawing of the moisture to the eyes; doth draw it to the nostrils by motion of consent; and so followeth sneezing.”

Later, scientists determined this to be incorrect as well, simply because the sneeze happens too quickly after the exposure to light. Watery eyes take time to develop.

This phenomenon went unstudied for the most part over the next 350 years. Finally, in 1964 a study started to shed a little more light on what was going on by proving that solar sneezes were actually a genetic trait. The study also showed that the trait was autosomal-dominant – meaning only one gene has “to be present for the trait to be expressed.” If one parent has the reflex than there’s a fifty percent chance their children will have it too.

In 1978, Dr. Roberta Pagon and her colleagues went further. While attending a birth defect conference, the subject turned to a lighter note, the solar sneeze. After a quick survey, four out of the ten doctors in the discussion explained that they and their families were prone to solar sneezes. Not only that, the times one sneezed during an “episode” seemed to be consistent within families, but different among each family. Explained Dr. Pagon, “One person said it was common for people in his family to sneeze five times; in my family it was three times, and another person said once.”

So, with this new piece of information, the doctors, as they are prone to do, dug deeper. Together, they wrote a paper on it and called the solar sneeze something a bit more scientific, autosomal dominant compelling helio-ophthalmic outburst syndrome, or “ACHOO”.

So what’s going on in the body to cause this? A study in 2010 done by University of Zurich professor Nicholas Langer attempted to figure this out by examining the different brain reactions of those who solar sneeze and those who don’t. He hooked up twenty subjects, ten with the trait and ten who didn’t, to an Electroencephalography (EEG) machine and exposed them to a bright light to measure their brain and neural responses. Dr. Langer came up with pretty surprising results, “The ‘photic sneeze reflex’ is not a classical reflex that occurs only at a brainstem or spinal cord level. It seems to involve other cortical areas of the brain.”

Given what he was seeing from the EEG’s, he came up with two theories why solar sneezes happen. The first one is that the visual system in the brain are simply more sensitive in solar sneezers. Overstimulation of light triggers a panicked response from other parts of the brain, including somatosensory system which controls sneezing. His other theory is a tad more complicated and actually renders Aristotle’s and Bacon’s notions not too far off, at least in part.

In this one, a sneeze is triggered by the nose being irritated, though unlike what Aristotle and Bacon proposed, moisture has nothing to do with it. The trigeminal nerve, responsible for certain facial sensitivity and motor control, senses this irritation. So what’s causing the irritation? The trigeminal is near the optic nerve, which sends visual information from the retina to the brain. So, when a sudden burst of light fills the retina and the optic nerve sends a signal to the brain to restrict the pupil, the signal could, in theory, be sensed by the trigeminal nerve and be mistaken by the brain as the nose being irritated- thus, the individuals sneeze.

Whatever the case, next time you walk out from a dark place into the bright light and your autosomal dominant compelling helio-ophthalmic outburst (ACHOO) syndrome, acts up, you know who to blame. Your parents. Well, the sun too, but mostly one (or both) of your parents.

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Bonus Facts:

  • The International Space Station orbits about 354 kilometers (220 miles) above the Earth and travels at approximately  27,700 km/hr (17,211 mph), so it takes about 92 minutes to circle the Earth once. For this reason, every 45 minutes the astronauts on-board see a sunrise or a sunset, with a total of 15 – 16 of each every 24 hours. Without proper visual protection, that’s a lot of sneezes for someone who has ACHOO syndrome.  Of course, without proper visual protection, sneezing would be the least of their problems when looking at the Sun.
  • Even though this is a relatively benign genetic trait, there are occupational hazards for several types of jobs. For instance, a paper published in Military Medicine in 1993 entitled “The photic sneeze reflex as a risk factor to combat pilots” notes that the reflex “could trigger an unexpected sneezing episode during critical periods of flight. This is an unrecognized and previously unreported danger to fixed-wing and rotary aircraft pilots.” While this is a risk, other sources say that a solar sneeze can be combated by simply wearing a pair of polarized sunglasses.
  • Some neurologists are also quite curious what causes the solar sneeze because they believe a study on this may give insight into other neurological disorders like migraines and epilepsy. As Dr. Louis Ptacek at the University of California, San Francisco stated in Scientific America in 2008, “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.”
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  • I read an interesting evolutionary theory on this once somewhere..
    It was theorized that in the time we were cave dwellers those with this response were naturally selected through better survival rates. It was proposed that the sneeze expelled the molds and viruses that would be found in the damp, cramped caves. Those who sneezed got sick less and therefore live to procreate longer.
    Not something that can readily be proven but an intriguing hypothesis.

  • Maybe not relevant but bless you when you sneeze in some cultures. When you hiccup means someone is remembering you in other cultures. When the palm of your hand itches means you will win some money in some cultures. There are some 4200 religions in the world as we speak. There must be at least a1000 different superstitions in the world.

  • Half the time, I can’t actually sneeze at all, unless I’m looking at the sun or a similarly bright light. Having a cold on a cloudy day is a especially miserable experience.

    • I sneeze both when suddenly exposed to bright sunlight or artificial light, and if I feel a sneeze coming on I can usually induce it by looking indirectly into a somewhat bright light. Cloudy days are the worst! When you have that tickle but you can’t quite get the sneeze to come out! I make the tickling sensation go away by closing my eyes for a few moments, it usually works.

  • On the other hand, when you feel a sneeze coming up and you don’t want to sneeze, staring at a bright light cuts the sneezing process. Staring at the sun is absolutely not advised.

  • Anyone who’s seen the “Nightcrawlers” episode from The Adventures of Pete & Pete already knew this.

  • I sneeze when walking outside, as soon as the sun’s light or a strong light source hits my face, I don’t have to be staring right at the source of the light, I even sneeze faster if I close my eyes.

  • I moved to Africa in the 1960’s and had this happen to me on arrival – I was told by the medics that the act of sneezing was an effort by my body to “stop down” the iris by pressure during the act ,and keep to excess light out . I accepted that as the answer – If i went into the shade or looked away from the bright area – the sneezing stopped .. Over to you for comments . .

  • Found this article quite interesting. I’m sure that people with this trait have similar experiences, but necessarily the exact same experiences. Take me, for example. These “solar sneezes” are the only sneezes that I get. Also, most bright lights do not trigger a sneeze for me, it has to be either the sun, or a reflection of it (such as off of a window, water, or snow). When I sneeze, I would estimate that it is only one sneeze about 8 out of 10 times, with 2 times that I get two sneezes. One more interesting thing, if there is anything separating me from the light such as a window, no matter how hard I try I won’t sneeze. Just thought I’d share how it works with me.

  • Neither of my parents have this trait but I do. It’s not only hereditary. Explain, scientists

    Inb4 adopted

  • I sneeze from bright lights . or the sun . on a cloudy day I can locate the sun because the heat or what light is still singing thru makes me sneeze, I sneeze up to 5 times and if I pinch the bridge of my nose I can sneeze more. I actually don’t mind the sneezin it it helps clear me out and if I have a cold it helps serverly to be able to sneeze on demand

  • Till today, I thought I was the only one with this kind of symptom.
    I’m highly allergic to lots of thing so sneezing is a daily part of my life, which is why I never paid any attention to the fact that the sun triggers sneezes.

  • I don’t sneeze when comin from the dark to the light. I do need to look at the light sometimes to help induce a sneeze that I can feel coming on. The reason I looked this topic up was because I could feel the need to sneeze while in bed (dark) and had to turn the light on my cell phone on to trigger the sneeze. Normally it’s 2 for me but tonight I only sneezed once. I still feel s slight need to sneeze and will probably not go back to sleep until I can trigger the secon sneeze.

  • Without digressing to the usefulness of such number of scientists wasting precious time on this (right, I had to)…. we in my family, when kids, noticed that when we took “quick peeks at the sun”, a sneeze would quickly come our way.
    Now as a grown up, I still use bright lights to induce an sneeze whenever I feel I need to… always works; like a swiss clock for me 🙂

  • My brother and I too have this type of sneeze but with a twist; I ALWAYS sneeze exactly two times when this happen, but my brother ALWAYS sneezes three times, without exception. Funny that.

  • My theory about this is that the sunlight is so bright that it shines through the skin on my nose and activates sensitive nose hair, which triggers the sneeze. When I’m about to drive out of the shade into the bright sun, and I know it will cause me to sneeze, I cover the bridge of my nose with my hand. That prevents the sneeze.

  • [x-post, YouTube, higher risk of it getting lost there]

    Well, if one parent haves the phenotype for ACHOO they either have the genotype Aa or AA, and the other parent that doesn’t have the phenotype would have genotype aa.

    If you cross Aa and aa, you’d get
    Aa, Aa, aa, aa (2/4, 50% chance of the phenotype, which is what you say in the article)
    If you cross AA and aa, you’d get
    Aa, Aa, Aa, Aa (4/4, 100% chance of the phenotype)
    If you don’t know which genotype the individual with the phenotype has (Aa (one ACHOO gene), or AA (two ACHOO genes)), which you don’t mention in the article, you have to combine the two, if you do that you’ll get a 75% chance of having the phenotype (6/8)

  • If one parent is homozygous for the sneezing trait, it will be apparent in 100% of the offspring.

  • I sneeze once and only once within 10-30 seconds when my eyes see the sunlight; faster when it is warm outside. After that, I will not need to sneeze again for at least a few hours even if I return to the sunlight.