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I am a sun sneezer. Which is also known as having the photic sneeze reflex
Or, the autosomal dominant compelling helio ophthalmic outbursts syndrome.
Which basically means if I go from a dark area into somewhere that's brightly lit - You know, like, looking at the sun - I will sneeze.
Wait for it...
There you go, I'm a sun sneezer.
But why does this happen?
People have known about this effect for at least a few thousand years
Aristotle was probably a sun sneezer because in his book of problems
he asked: Why does the sun provoke sneezing?
And his answer was it was the heat from the sun which causes
sweating inside your nose, and so you sneeze to get rid of the moisture.
but a couple millennia later
Sir Francis Bacon demonstrated that this could not be the case because when he closed his eyes and turned towards the sun
well he did not experience that photic sneeze reflex so his explanation was that it was the eyes
watering and then when some of that moisture got down into the nose that caused the tickle which makes you sneeze
but even this theory has its problems because eye watering is a much slower process than the photic sneeze reflex
So it can't be the cause. Before I started researching sun sneezing
I thought that having the photic sneeze reflex
Must Convey some sort of evolutionary advantage under the people who have it. If you think about it
Sneezing is a way of transmitting disease. In your snot there can be the living Bacteria that cause
Tuberculosis, and strep throat or viruses that cause measles mumps Rubella and influenza, so if you're living in a moist dark cave
and you sneeze
Where your snot lands on the floor or the walls of the cave and those Pathogens can stay alive for hours or even days
increasing the Likelihood of spreading that disease to other people who live with you in your cave
Whereas if you only sneeze when you emerge from the darkness of the cave and into bright sunlight
Well, then that mucus will quickly dry out or because it's exposed to the harmful UV rays of the sun
It will kill all of those pathogens
Greatly decreasing the risk of spread of disease
By the 1960s some studies were revealing the hereditary nature of the photic sneeze reflex
There was a father who would sneeze two times when he entered bright sunlight
And when they tested his baby daughter who was just four weeks old
Moving her from a dark room into full sunlight also caused her to sneeze
Exactly two times and by the 1980s it was clear that this trait was
autosomal dominant
Meaning that you only needed to inherit one
Copy of the Gene from just one of your parents in order to exhibit the trait
But when studies the population have been done only about 18 to 35 percent of people actually have the photic sneeze reflex
So I don't really think this gives a great evolutionary advantage, otherwise everyone would have it
you know it could just be one of those random mutations that happens over time and
Sustains itself because it's neither good nor bad evolutionarily speaking
So it affects roughly one in four people
Can you spot the person with the photic sneeze reflex?
Nowadays, it's actually been found that the gene responsible for the photic sneeze reflex is on the second chromosome
And it's a single letter of DNA that's been changed, on my second chromosome
I have a C
Where non sun sneezers have a T, and the reason that we know this is that back in 2010 there was a study of about
10,000 people where they went online and they
Reported whether they were sun sneezers or not and then their DNA was
analyzed and the groups were compared and what they found was the thing the sun sneezers had in common was this one particular
letter change in their DNA.
That I think is pretty amazing.
Now it's unclear exactly how this change affects your physiology and makes you more susceptible to sun sneezes
But the best theory at the moment is that it involves the trigeminal nerve which is the largest cranial nerve it
Involves all of the feeling that you have in your face and as the name implies
It actually has three branches one of which receives stimuli from your eye and another which receives stimuli from your nose
so the thought is that this really active stimulation of the optic nerve may cross over into the
maxillary Branch causing that little tickle which gets you to sneeze
Photic Sneezes are generally pretty harmless unless you're doing something like flying a fighter jet or performing some sort of delicate surgery.
But this methodology,
can allow us to learn a lot about different heritable traits and diseases just by studying lots of people and their genotypes
This episode of veritasium was supported by 23andme. Which is actually the company that figured out that gene polymorphism
responsible for the photic Sneeze reflex
the name of the Company 23andme comes from the fact that humans actually have 23 pairs of chromosomes and
The purpose of the company is to give people insight into their own DNA
So what you do is spit into a vial
which is actually much harder than it sounds and
Send it off to them and of course in your saliva are some of the cells from your mouth
They analyze the DNA from those cells
And then they send you a report where you can find out tons of stuff about your genes like
Where do your genes come from that is what's your ancestry and do you have the photic sneeze reflex? Do we share the same?
Change of DNA on our second chromosome you can also learn about your health and other physical traits and how much
Neanderthal you are so if you want to learn more about your genotype
Then you should go to, so I want to thank 23andme for supporting me
And, I want to thank you for watching.