2017-04-27

[public] 2.23M views, 101K likes, 1.18K dislikes audio only

Veritasium

I have the photic sneeze reflex so I sneeze when I look at bright light.

Check out 23andMe: http://ve42.co/23andme

*So technically the single nucleotide swap (C instead of T) is not actually in a gene per se but in an intergenic region on chromosome 2. It's also not clear exactly how this affects physiology or causes the sun sneeze but there is correlative evidence that every copy of this single nucleotide polymorphism (SNP) is associated with a 1.3x increase in likelihood of having the photic sneeze reflex.

I have wanted to make a video about sun-sneezing for a long time. It is something I've experienced my whole life. When I go from a dark room indoors into full sunlight I invariably sneeze. I thought everyone did it. So my original question was why do people sneeze when they see bright light? That led me to consider what possible evolutionary advantages there could be to sneezing in sunlight. The obvious advantage to me is that sunlight kills pathogens of which there may be many in your snot or mucus. So sneezing in sunshine is a much better idea than sneezing inside a dark, damp cave where you may be living.

For more info, check out:

Web-Based, Participant-Driven Studies Yield Novel Genetic Associations for Common Traits

http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1000993

Filmed by Raquel Nuno