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?

Related Posts


comments

All comments are moderated, your comment will not appear on the site until it has been approved.

  1. Both my husband and I are sun sneezers…only to the effect that we can help ‘push’ a sneeze along by looking up at the sky. Our little daughter however is a full-on sun sneezer. She will sneeze every time she goes out in to the sun and then periodically if we stay outside. She has the talent of being able to ‘make’ herself sneeze simply by looking up at the sky…she can usually only do it once though. It’s very helpful when she has a stuffy nose…i say, lets go outside and sneeze…loosens up that snot quite quickly

    Angelina B, November 5, 2014 at 3:20 pm
  2. I am also a sun sneezer , i sneeze everytime i see the sun especially in the morning and also when i expose to sunlight after adaptng to dark and have used it often when I felt a sneeze coming on.

    Ashna gupta, November 12, 2014 at 5:56 am
  3. I found everyone’s input on this subject was interesting and inquisitive. I don’t think the people on here calling people dumb etc. are very educated either for they should know the rule of thumb that no question is a stupid one. It is an attempt to gain knowledge. Sorry for all this but after I read the comments that were put downs, I found them very rude.

    Adrienne, November 14, 2014 at 2:31 pm
  4. i am a person who has photic sneeze reflex and yes i use this as an advantage to get rid of a sudden urge to sneeze while i am exposed out in the sun. this passage i thought was very helpful i thought that this was a trait that all human beings shared, but turns out only select individuals depending on their genetic traits passed down from generations have photic sneeze reflex.

    tommy trainor, December 18, 2014 at 12:42 pm
  5. I guess iam suffering photic sneeze reflect but i dont like its abit…i sneeze every morning 8 to 10 time and its cause me painful around my hold body,sometime even my tear come out unable to bear the sneeze i guess..and after the sneeze end i find my nose watery and even inside my nose its like something inside its and make me feel iritating..but it only happen in everytime i wake up and go for a brush its has no fixed time and all the symtom or problem end after an hours

    sarchesong kramsa, January 29, 2015 at 2:36 am
  6. Really enjoyed the article and discussion. My husband and I just had our first daughter 2 months ago and her morning/after nap sneezes had reawakened the sun sneeze debate in our house. Hubs has always thought me nuts for believing that bright sunlight makes me sneeze. Especially when we were sharing a car for a while, we’d take a turn toward the highway each morning and like clockwork (on a sunny morning that the windshield gets flooded) I’d sneeze. I remember my blue eyed mom trying to explain to me when I was little, that it was because of mu light green eyes (and why my blue eyed sister also sneezed with sunlight and my brown eyed dad, sister, and brother didn’t). Now my blue eyed (so far) daughter and I carry on this oddity and keep my husband delightfully puzzled.

    Joy, February 28, 2015 at 8:10 am
  7. I’m 17 at the moment and every time I look at the sun I sneeze. It’s been that way for as long as I can remember. Even now I’ve started to sneeze every time I eat any kind of food at every meal I have. Never really gave much thought to any of it tbh.

    Victoria, April 28, 2015 at 5:50 pm
  8. I have continuous sinus drip in sunshine and it goes away when it clouds over or it is 4pm till around 9 am

    yvonne, May 19, 2015 at 12:58 pm
  9. Well, that’s odd. I only sneeze when I simply step into sunlight, but it is specifically when I’m outside, and is daytime. If I go outside at night, I won’t sneeze. Bright light doesn’t make me sneeze either, so I feel like this article really didn’t explain what is going on with me.

    Chris, July 17, 2015 at 1:06 pm
  10. As yet another sufferer i also have speculated about the cause. I cannot speak for others but bright lights besides the sun do not affect me…. it makes me wonder if perhaps the sneeze is a built in defense mechanism. We are now only too aware of the suns damaging rays…when we sneeze we generally look down…but it definately forces us to close our eyes…perhaps its your body telling you to look away from the sun.

    Tom Derri, November 26, 2015 at 11:45 am
  11. I also Suffer from this odd condition but I have noticed it is any change in light patterns. For instance if a glare from chrome or a bright light off glass is reflected at me I will sneeze usually several times in a row. It does not have to be sunlight. I have even been able to catch myself and slow the process down but my eyes still water quickly. I hope they will research this it would be nice to know what else is linked to this condition.

    Michael Ulshafer, December 24, 2015 at 11:05 am
  12. I’ve always been a sun sneezer, & when I eat chocolate. Usually the darker chocolate.

    Jess, December 26, 2015 at 5:35 pm
  13. This is interesting because i wake up fine and then when i go down the stairs and open up curtains to my back garden im usually blinded by the light esl in the spribg/summer and i end up sneezing three to four times before i even move from the window

    Katie, January 8, 2016 at 8:51 pm
  14. This is so weird and would explain why when i get up to open the curtains in my living room particulary on a sunny day, im blinded for a seccond and before i get chance to move from the window i sucumb to a sneeze, or more until i move from the window

    Katie, January 8, 2016 at 8:57 pm
  15. Over 50 years lifetime sun sneezer. I can also induce a sneeze by looking at a bright source of artificial light while indoors.

    Paul, January 16, 2016 at 12:47 pm
  16. I always sneeze when I look at the sun ,maybe 2 to 3 times ,my brother too and now his son also,we all have blue eyes,and wondered if this could be the reason,I also think this could just be a natural defence system from your body,because what do you do when you sneeze? you close your eyes!

    Del, February 1, 2016 at 12:13 pm
  17. My bird is actually the one who is the sun sneezer! Oddly enough, he is a sun conure who we always giggled about being allergic to the sun, because when a sun bean hits him he sneezes! Someone just pointed out to me that it was a human thing too.

    Rebekah, February 26, 2016 at 6:40 am
  18. This happened to me occasionally when I was younger. I’m 37 now, kinda wondering why it doesn’t happen anymore. I think now I usually close my eyes as soon as the sun hits me so that they adjust slowly. I also do the one eye open technique until it adjusts then open the other. Btw. My eyes are brown.

    Pmp, May 6, 2016 at 7:22 pm
  19. … maybe in some people their eyes don’t adjust fast enough so to protect the eyes from the sun the sneeze reflex is triggered and the eyes close which gives pupils time to adjust. Maybe, like other parts of the body, sneezing makes the pupils contract faster.

    Pmp, May 6, 2016 at 7:30 pm
  20. I am also a photic sneezer. I think it’s a handy trick but I guess I don’t have some of the problems others do. If I have a sneeze stuck I can look into a bright light, like a lamp with a 60 watt bulb in it and make myself sneeze and that takes care of it. For light to make me sneeze if I’m not even close to sneezing it has to be a situation like having gone to a matinee and sat in a dark theater and walk out directly into the sun. Up until recently I also thought it was something everyone could do.

    lillyc, May 14, 2016 at 9:36 pm
  21. I only last year learned this wasn’t the norm, I always thought t happened to everyone!

    Laura, June 5, 2016 at 6:04 pm
post your comment