1 00:00:02,000 --> 00:00:07,040 Speaker 1: Welcome to brain Stuff from how Stuff Works. Hey, brain stuff. 2 00:00:07,080 --> 00:00:10,239 Speaker 1: Lauren vog obam here with today's question, why do some 3 00:00:10,320 --> 00:00:14,240 Speaker 1: people sneeze when suddenly exposed to bright light like sunlight? 4 00:00:14,920 --> 00:00:18,520 Speaker 1: Only about ten to of people do this. I happen 5 00:00:18,560 --> 00:00:21,040 Speaker 1: to be one of them, And no, we're not allergic 6 00:00:21,079 --> 00:00:23,560 Speaker 1: to the sun. We may be the proud owner of 7 00:00:23,560 --> 00:00:27,440 Speaker 1: a photic sneeze reflex or PSR, also known as at 8 00:00:27,520 --> 00:00:31,320 Speaker 1: Chew syndrome. And yes, that's an acronym. It stands for 9 00:00:31,400 --> 00:00:37,000 Speaker 1: autosomal dominant compulsive helio ophthalmic outbursts of sneezing. And don't worry, 10 00:00:37,000 --> 00:00:39,280 Speaker 1: we'll get back to some of those terms in a minute. 11 00:00:40,120 --> 00:00:42,320 Speaker 1: People have been trying to figure out the cause of 12 00:00:42,320 --> 00:00:46,040 Speaker 1: the photic sneeze for thousands of years. The ancient Greek 13 00:00:46,040 --> 00:00:50,000 Speaker 1: philosopher Aristotle or an unknown author writing in his name, asked, 14 00:00:50,360 --> 00:00:52,760 Speaker 1: why does the heat of the sun provoke sneezing and 15 00:00:52,840 --> 00:00:56,480 Speaker 1: not the heat of the fire? Good question, Aristotle or 16 00:00:56,520 --> 00:00:59,720 Speaker 1: fake Aristotle's answer to himself was because the heat of 17 00:00:59,720 --> 00:01:03,480 Speaker 1: the sun doth dissolve but not consume, and therefore the 18 00:01:03,600 --> 00:01:08,560 Speaker 1: vapor dissolved is expelled by sneezing, So His theory is 19 00:01:08,600 --> 00:01:10,560 Speaker 1: that the heat of the sun makes the inside of 20 00:01:10,600 --> 00:01:12,880 Speaker 1: your nose wet, and you've got to purge that liquid 21 00:01:12,920 --> 00:01:17,400 Speaker 1: with a good sneeze. Unfortunately, in the seventeenth century, the 22 00:01:17,440 --> 00:01:20,800 Speaker 1: English science pioneer Francis Bacon decided to put Aristotle to 23 00:01:20,800 --> 00:01:23,640 Speaker 1: the test. He showed that if a photic sneezer walks 24 00:01:23,680 --> 00:01:25,959 Speaker 1: into the sun with his or her eyes closed, the 25 00:01:26,000 --> 00:01:29,400 Speaker 1: reflex is not triggered. Therefore, we know it's not caused 26 00:01:29,400 --> 00:01:32,440 Speaker 1: by the heat. It's caused by your eyes reacting to light. 27 00:01:33,080 --> 00:01:36,240 Speaker 1: So what do we know about the photic sneeze today, Well, 28 00:01:36,480 --> 00:01:40,160 Speaker 1: one study in found that it's not any particular wavelength 29 00:01:40,200 --> 00:01:42,919 Speaker 1: of light that causes the problem, So you can't protect 30 00:01:42,959 --> 00:01:45,639 Speaker 1: against it by just filtering out red light or violet 31 00:01:45,720 --> 00:01:48,680 Speaker 1: light or anything in between. Instead, it has to do 32 00:01:48,760 --> 00:01:51,680 Speaker 1: with the intensity of the light. So the good news 33 00:01:51,800 --> 00:01:53,800 Speaker 1: is that if you want to avoid the photic sneeze, 34 00:01:53,960 --> 00:01:56,480 Speaker 1: there's a pretty easy solution that works most of the time, 35 00:01:56,840 --> 00:02:00,960 Speaker 1: plain old sunglasses. Also more good news. If you're one 36 00:02:01,040 --> 00:02:03,840 Speaker 1: of the seventy to nine of people listening and thinking, 37 00:02:04,200 --> 00:02:06,560 Speaker 1: what on earth is she talking about? Am I going 38 00:02:06,600 --> 00:02:10,280 Speaker 1: to catch this sneeze? Disease. Someday you can rest easy. 39 00:02:10,680 --> 00:02:13,720 Speaker 1: You can't acquire the photic sneeze reflex after birth. It's 40 00:02:13,720 --> 00:02:16,960 Speaker 1: a genetic trait. A study in the nineteen sixties found 41 00:02:17,000 --> 00:02:20,640 Speaker 1: that this trait is inherited through an autosomal dominant mechanism. 42 00:02:20,639 --> 00:02:23,080 Speaker 1: This means that it doesn't matter which of your parents 43 00:02:23,120 --> 00:02:26,040 Speaker 1: has the photox sneezing gene. If one of them has it, 44 00:02:26,320 --> 00:02:28,360 Speaker 1: you have a fifty percent chance of being a photo 45 00:02:28,440 --> 00:02:33,679 Speaker 1: sneezer yourself. But the question of why remains. No absolutely 46 00:02:33,680 --> 00:02:37,320 Speaker 1: conclusive answer has been reached, But there's one very interesting theory. 47 00:02:37,800 --> 00:02:42,120 Speaker 1: Photox sneezing happens because some wires are crossed in your head. Normally, 48 00:02:42,160 --> 00:02:45,000 Speaker 1: a sneeze is your noses version of the passenger eject 49 00:02:45,080 --> 00:02:48,920 Speaker 1: seat in James Bond's car. Sneezing begins when irritation in 50 00:02:48,919 --> 00:02:51,760 Speaker 1: the nose is detected by an organ called the trigeminal nerve. 51 00:02:52,120 --> 00:02:55,440 Speaker 1: When that nerve senses an unpleasant foreign substance, it sends 52 00:02:55,440 --> 00:02:58,560 Speaker 1: the eject signal to the brain. But inside your head, 53 00:02:58,919 --> 00:03:01,720 Speaker 1: this nerve runs very close to the optic nerve, which 54 00:03:01,720 --> 00:03:05,080 Speaker 1: senses light in the eyes. So let's say the eyes 55 00:03:05,080 --> 00:03:08,040 Speaker 1: of a photo sneezer are suddenly exposed to bright sunlight. 56 00:03:08,400 --> 00:03:11,480 Speaker 1: The optic nerve detects this and sends another reflix signal 57 00:03:11,919 --> 00:03:15,320 Speaker 1: too bright drink by pupils. But if the optic nerve 58 00:03:15,400 --> 00:03:17,920 Speaker 1: runs a little too close to the trigeminal nerve, the 59 00:03:17,919 --> 00:03:21,480 Speaker 1: pupil constriction signal also gets interpreted as a something's in 60 00:03:21,520 --> 00:03:30,280 Speaker 1: my nose signal and Bam sneezing fit. Today's episode was 61 00:03:30,320 --> 00:03:33,000 Speaker 1: written by Joe McCormick and produced by Tyler Clang. For 62 00:03:33,080 --> 00:03:35,000 Speaker 1: more on this and lots of other topics about our 63 00:03:35,080 --> 00:03:49,680 Speaker 1: weird bodies, visit our home planet, how Stuff Works dot com.