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

Why do some people sneeze when they look at the sun?
Sudden exposure to sunlight makes some people sneeze. [Credit: Wellcome Library, London]
By | Posted November 9, 2009
Posted in: Ever Wondered?
Tags: , , ,

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.

Posted in: Ever Wondered?

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  1. As a child whenever I was about to sneeze my mum or dad would tell me to look at a bright light, so I grew up thinking this is what everyone did.

    Thanks for an interesting article.

    Jo Brodie, November 10, 2009 at 5:12 pm
  2. Or, it could be that looking into a bright light makes your eyes water, which causes your nose to run, which creates more mucous which triggers the sneeze reflex.

    Mandamus, November 10, 2009 at 6:31 pm
  3. Add me to the list of anecdotes who can hasten the sneeze by looking towards the sun.

    But I don’t like the way that those UCSF people implicitly characterize it as a “disorder”. And there’s a “support group”? Do people really need emotional support for this? Strikes me as overkill.

    Paul Clapham, November 12, 2009 at 5:19 pm
  4. I enter a bright ray of light. I squint my eyes. Doing so my facial muscles also flex my nose. Dry boogers fracture and pierce senstive nerve endings in my nose triggering tear duct response. Tickled nose + Tear ducts pumpin in squinted position = SNEEZE! Sometimes 2 sneezes. Followed up by facial tissue to blow my nose to clear debree and tears. I never needed a scientist to explain this to me.

    NeeAnderTall, November 13, 2009 at 3:46 am
  5. You people are all fools.

    I discovered the answer to this mystery after my son was born. In the morning, when ever he woke up and the sun hit his face, we would immediately sneeze, clearing out all the mucus that has built up over the night. Babies that have this reflex therefor have less nasal congestion and so fewer upper respiratory infections and thus were more likely to live long enough to have children themselves.

    Case closed.

    Patrick McGroin, November 13, 2009 at 2:45 pm
  6. I have some strange experience related to sneezing, though not the sun.

    Whenever I focus on a certain thought/topic/mechanism etc in order to reveal what is behind it (like reading between the lines) I sneeze and lose concentration.
    Which is why I sometimes cannot accomplish what I am trying to do (i.e. to understand a complex structure)

    can someone explain that, seriously. I am not a kid, I am 24 years old, and finished college, going for a post-graduate degree. So, this sneezing thing makes me uncomfortable.

    sayid, November 22, 2009 at 10:15 am
  7. I’m always interested in this topic. I sneeze when I think about sex, and it was interesting to find out that other people shared and were aware of my peculiarity.

    Adam Huddleston, December 11, 2009 at 1:27 am
  8. i sneeze

    jack, December 11, 2009 at 12:31 pm
  9. That is an absolutely disgusting photo.

    Kimberley, December 11, 2009 at 4:38 pm
  10. For some reason all the males from my father’s side (my dad and his brothers, his dad, my brothers and I) of the family have this sunlight-induced sneezing reflex.

    Curiously, none of the females in our family seem to have inherited this trait.

    Drew Barnard, January 6, 2010 at 7:29 pm
  11. My family is just like Drew’s. The reflex only seems to occur on the male side: my grandfather, his son (my father), my brother and I.

    But we are affected to different degrees, my grandfather and I more than my father or brother. This means that once my brother or father have gone out into the sun and sneezed, they will be right for the rest of the day. It can happen to me pratically every time I appear into the sunlight from a dark place. Can be a menace when you are driving.

    Martin, February 1, 2010 at 9:24 am
  12. I too am a sun sneezer. For years I never met anyone else that did so. I have always found it to be funny. I hope all those people who consider it a disorder get help. As for me, I usually only sneeze once, not multiple times. Do some people sneeze over and over?

    Lewis, March 4, 2010 at 3:57 pm
  13. Wow, I can’t believe how stupid some people can be. I have the photic sneeze reflex too. It is not a disorder, it is NOT caused by mucus, and my son also has it. If you think you are smarter than some of the scientists who actually study this than go right ahead and tell your idiotic comments. You can’t say it caused by mucus just because your baby did it. Not everyone is the same. And by the way I’ve never had a problem with mucus when i sneeze from looking at the sun.

    Bonnie, March 29, 2010 at 2:48 pm
  14. This happens to me too but not naturally, I have to make myself do it by focusing on the sky (The sun is too bright to look at, therefore I can’t make myself sneeze by looking at it). I can also do it with florescent lights.

    I feel bad for people who can’t do it :D

    Megan Fleming, June 4, 2010 at 8:29 am
  15. God that picture is so friggin gross!

    Megan Fleming, June 4, 2010 at 8:37 am
  16. I thought everyone sneezed when exposed to light! I always do 3 in a row then a fourth a few seconds later. It’s a nightmare when I’m driving and sunglasses don’t help. I get it when using my computer at work too. I quite like it!

    Anouska, October 26, 2010 at 5:00 pm
  17. I’m pretty sure it’s NOT caused by tear ducts causing more mucous considering the fact that the tear ducts are much too slow a reaction as opposed to a sneeze to be a causal relationship. That much has been proven. I find it really interesting that some of the commenters only had men in the family who sun-sneezed. It affects my brother and my dad, but I have it the worst (or best in my opinion) and I’m female. This happens to me anytime I step into a bright light from a dark place, and I can sneeze with basically any light if I need to. (I frequently use the bathroom lights.) It’s cool to see the different types and intensities of sun-sneezers. Thanks for the article!

    Sarah, November 3, 2010 at 3:06 pm
  18. I always sneeze when I look at the sun, or just a bright light. Actually, whenever I feel the need to sneeze, but I just can’t get it out, I always look at the brightest light around me so I can sneeze. 9 out of 10 times it works.

    Emily, November 18, 2010 at 10:30 pm
  19. I always have thought everyone did this like me! So funny to hear otherwise.. My husband gets a kick out of it because I do it if I hold my cell phone light up, any lights in the house, and ALWAYS the sun. I make myself laugh too. No disorder.. Just a strange gift :)

    Kayleigh, November 29, 2010 at 1:16 am
  20. I’ve always wondered why I sneeze when I see the sun at times. I hope they find a conclusive answer for why it happens, and of course how. I have other allergies that make me sneeze, so I think it’s interesting that maybe one day scientists will find a cure for people who are, allergic to the sun, in a way, haha. :]

    Katrina, January 29, 2011 at 10:18 pm
  21. this is so turue…i asked a scientist i know and he told me the same thing…so funy

    noneofurbussines, February 3, 2011 at 4:58 pm
  22. To tell you the truth I dont think its caused by any of the reasons they put here. I think that it is a reflex caused by your body to protect your eyes from bright light. because it is impossible to keep your eyes open when you sneeze and when you sneeze your head will move and out of the way of the sunlight or bright light. thats what I think

    Ethan, February 24, 2011 at 1:54 am
  23. I have the photic sneeze reflex as well, I think mine is perhaps more profound than others with the reflex. I usually only sneeze once but I think I’m especially suspectible to light, I can trigger a sneeze with a dim incadescent bulb and even flurourescent lights (but those tend to be more difficult for whatever reason). Additionally, I’ve been noticing that I can now sometimes trigger a sneeze just by looking up, even if there is no light on above me. Perhaps this is common to all people? I think an interesting idea would be to do a study to see if photic sneezers enjoy sneezing more than non-photic sneezers. I have a feeling we do…but I guess that’s why somebody else should run my study for me.

    Rich, April 5, 2011 at 12:16 pm
  24. Are you sure that it is the sun that makes you sneeze? Or the sun that makes you Perspire and a cool wind that comes in contact with the skin when you are only wearing a light jacket. 99% of the time when this occurs to me I know to go in and put on a sweater or a sweat shirt and the sneezing stops

    vanzante, January 20, 2012 at 1:19 pm
  25. My wife calls me a vampire, I sneeze twice most of the time. More on other days, if I feel a sneeze coming on I can usuwally stare at a bright light and get it out. It does feel great afterwards.

    Christian, February 27, 2012 at 6:44 pm
  26. I thought it had something to do with squinting your eyes. Squinting might constrict a sinus passage which could lead to a sneeze. Maybe pressing on a nerve?

    Bill Walters, March 9, 2012 at 3:56 pm
  27. I have always been a sun sneezer from as far back as I can remember. Bright light bulbs help me sneeze too. I used to think that the sun made everyone sneeze. Now I realize that’s not true and I often look like an idiot staring up at the bright sky to try to sneeze. My son does it too but my daughter doesn’t. It’s funny, when we walk out of a store and the sun hits us, usually I sneeze first and he goes a few seconds after me. My daughter just laughgs.

    Ginny, March 31, 2012 at 3:05 pm
  28. Besides sun-sneezing, I also often get rashes because of sunlight. I always thought sneezing was part of larger allergy to sunlight that I might have had. But my skin reaction has decreased in thre last one year but sneezing remains. Now I know they are both separate engities.
    Although often I have to push the first sneeze over the threshold. I usually get 3-5.
    I like sun-sneezing :-D

    Nitish, May 4, 2012 at 10:54 pm
  29. My father and I are also sun sneezers. My mother does not have it. I always thought that most people sneeze when they see bright lights. Me and my father only sneeze when we see the sun though. If it is an autosomal dominant trait and from what I read in these comments mostly occurs in men and is passed on hereditarily, then it is possible that it is linked to the X chromosome, like color blindness

    John, June 5, 2012 at 7:21 pm
  30. I often sneeze whenever I try to make myself cry on command (for acting purposes, not for manipulative purposes or anything haha). Also, I don’t sneeze just by being exposed to sun, but if I can already feel a sneeze coming on (not as a result of lighting), lifting my head up into brighter light source helps to speed up the sneeze. I don’t deny that there are some photic sneezers, but maybe it’s the placebo effect for me when it comes to the light thing.

    Gab, June 14, 2012 at 4:40 am
  31. I’m the only one in my family who can do this. Since way back when I was kid, if I want to sneeze I would just look up at the sky when its bright (not necessarily the sun)and I would sneeze lol.

    Daryl, June 16, 2012 at 12:01 am
  32. My son, now 14, has always sneezed when he walks outside…coming out of the house, getting out of the car, anytime he encounters the light change to the bright sunshine he sneezes, but only once. To the person above who commented it helped as a child, didn’t help us. He had the croup and other nasal problems as a small child. Glad we googled this and now have a name to put with it!

    Jackets11, July 20, 2012 at 11:02 am
  33. I never had this as a child, but I developed it as an adult. I sneeze violently, three-four times, when I go in the sun. I think it might have to do with dry eyes. I don’t have any tears to speak of, and my eyes are more vulnerable now. I tend to blink and squint more in the bright light, and that may be what sets it off. Just an idea. My mother also had this, and she used to sneeze 10-12 times in a row, even when the eye doctor shined a little flashlight in her eye. So I guess it must be inherited. I agree, it’s VERY dangerous when you’re driving. Who knows how many accidents have been caused by these sneezing fits? Doesn’t seem to be any way to cure it, though, even sunglasses don’t help me.

    Kathy Poetzsch, July 20, 2012 at 11:14 am
  34. I have the sun sneezing problem it occurs whenever any bright light hits my eyes ,often resulting in 4-8 violent sneezes which leave me feeling pretty awful and beat up wondering if that is normal for sun sneezers

    Brian lokey, February 17, 2013 at 5:36 pm
  35. I also am a sun sneezer and have used it often when I felt a sneeze coming on. I also sneeze when I pluck my eyebrows. I even told my children when they were younger to look at a light when they’d say they felt like they had to sneeze. I had always thought everyone was that way. I am female and my son and daughter are both sun sneezers……My mother was not, not sure about my father, he passed away when I was 11 before I knew to ask him.

    Cheryl, February 21, 2013 at 10:53 am
  36. The only two people in my family that I know are “sun sneezers” is my father and I. Though I’m a bit different. I don’t sneeze whenever I’m suddenly exposed to sunlight for the most part. It’s generally right after I wake up from a nap or something and the room is still dark, I roll over to grab my iPad and a few seconds after the screen illuminates I sneeze, but only once. It’s when I still have that feeling you get right after you wake up in the morning and you’re dreading turning a light on because you know it’s going to hurt your eyes. My father is a true “sun sneezer.” Whenever he walks outside into the sun from an especially dark room, he’ll sneeze. I don’t know how many times he sneezes on average, but mine is only once or twice, regardless if the sneeze was due to the sun or not.

    Clay, March 12, 2013 at 11:30 pm
  37. I sneeze every morning when I wake up.I was sleeping soundly with nice dry unblocked nose but as soon as I open my eyes a sudden almost violent reaction starts in my nose and I can the runny mucous coming down and sneezing starts.doctors n others always categorizeed it as allergy but I knew it’s related to exposure to light.I started searching for info on this.everywhere a lot of ppl are having this
    prob n being termed as having allergy.they have tried all cures still they sneeze.only after I read the above article I thought it has nailed my problem.it talks about genetic and I can claim that both my parents suffer from the same prob.(though they always think it’s allergy).as I suffer

    Yasmeen, April 13, 2013 at 3:00 am
  38. I suffer from allergies as well so I know my patterns and I can def say theres some connection between exposure to light and runny nose n sneeze.I react when I look at my mobile in a dark room.I react when I open my eyes in the morning.it goes away after an hour of waking up.also sometimes staring at computer triggers it.no wonder antihistamines didn’t help.some dry up the mucous but def. This is smting to do with light.

    Yasmeen, April 13, 2013 at 3:06 am
  39. The color of the eyes is the answer..

    Brown … No sneeze. Other colors yes

    Dj

    David F. "Dj" Johnston, September 15, 2013 at 9:33 am
  40. You know, as a child I thought it was a way to make you stop looking at bright lights suddenly, because staring at the sun is bad and dramatic light changes sometimes hurt my eyes. Too bad the current theory is that my brain just glitches a little. :P

    Kaiti, September 24, 2013 at 10:27 pm
  41. Also, my eyes are brown…one could argue hazel in certain lights. :P

    Kaiti, September 24, 2013 at 10:31 pm
  42. Anyone notice that when you feel a sneeze come on and try to get it to happen by staring at a light, if it fails and you cant sneeze it turns into a yawn?

    Kaiti, September 24, 2013 at 10:40 pm
  43. I have problem of sneezing and nose flowing and this is happen whenever set under or in front of fun, sleeping on one side, one hole of nose stops, or walking in environment of dusty and itching my nose and than flowing. please advice me to obtain the tablet or injection.

    Naim, October 13, 2013 at 3:25 am
  44. i´m a sun-sneezer and also menthol-sneezer….in 100% cases i eat something containing menthol, i sneeze immediately.

    and i have dark brown eyes

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