On The Photic Sneeze Reflex

I remember being told by one of my classmates in first grade that if I wanted to artificially induce a sneeze, all I had to do was stare at a light source, such a lamp or the sun. I tried it out at recess the next day and, sure enough, looking up at the sun really did make me sneeze. What a cool trick!

Over time, I became more cognizant of the fact that I actually did tend to sneeze pretty often when it was sunny. I noticed that it was especially likely to happen after emerging from somewhere dark, like a building or car. It was a change in light, from dim or artificially lit to bright and sunny, I learned, that makes people sneeze.

Well—makes some people sneeze. It wasn’t until late high school that I found out not everyone actually sneezes when they look up at the sun. My gym class was going outside to the soccer fields one particularly sunny spring day. When my friends and I stepped outside, I immediately sneezed three times as I normally do on a bright day. One of my friends turned and asked if I had allergies.

“Nope, it’s just the sun,” I told her pretty matter-of-factly.

“Just the sun!?” she repeated. My friends all laughed, thinking I was joking.

But I wasn’t. And I was genuinely confused why they didn’t understand. Everyone knows looking up at the sun makes you sneeze! How had they never noticed it before? My friends and I argued for a few minutes, but couldn’t come to a mutual agreement on whether the sun can actually make you sneeze or not.

I was determined to prove that I was right about sun sneezing, so I spent the rest of the afternoon doing some research. What I found was actually quite interesting.

It turned out, sneezing after staring at the sun is a real thing! In fact, it even has a name: the photic sneeze reflex (PSR). Unlike what I had originally believed, however, not everyone has the photic sneeze reflex. In the U.S., it’s estimated that anywhere from 10 to 35 percent of people sneeze at the sun. And, as I had noticed with myself, it’s not the sun alone that causes sneezing; rather, a change in brightness (usually caused by looking at the sun after coming out of a building) induces the sneeze.

The photic sneeze reflex is a genetic condition that is inherited in an autosomal dominant manner. This means that you only need to receive the gene from one of your parents to also have the photic sneeze reflex. The genetic nature of sun sneezing led one group of scientists in the ‘70s to coin an alternative name for the condition: ACHOO, or the Autosomal-dominant Compelling Helio-Ophthalmic Outburst syndrome.

It’s not known exactly why a change in light intensity makes individuals with the PSR gene sneeze, but one of the more compelling theories is that there is an unusual connection between the nerve that responds to light (the optic nerve) and the nerve that controls facial movement (the trigeminal nerve). Normally, these two nerves don’t communicate much with one another, but in the case of the photic sneeze reflex, stimulation of the optic nerve by a sudden bright light shining on the retina of the eye results in stimulation of the trigeminal nerve, which moves the muscles around the mouth and nose to form a sneeze. This is similar to what happens in individuals with synesthesia, a condition where two or more distinct senses are combined so that an individual may, for example, be able to see a color when a certain musical note is played.

Obviously, the photic sneeze reflex is not as pressing a medical concern as something like cancer or neurodegenerative disease, so there are few groups that study the syndrome. Still, some scientists hypothesize that the gene for the photic sneeze reflex may be linked to genes related to epilepsy or migraines, two disorders associated with light sensitivity. This is especially interesting for me because, though my mom doesn’t have the photic sneeze reflex, she does get pretty severe migraines and in general has sensitive eyes (she never leaves the house during the day without sunglasses). Perhaps the genetic mutation that causes my mom’s migraines and eye sensitivity is related to the one that causes me to sneeze when I see bright lights.

I’m proud to have the photic sneeze reflex. Being able to sneeze on command and in response to sudden bright light is kind of like having a superpower––a fun, but perhaps kind of useless, superpower. The photic sneeze reflex is a quirk that not a lot of people know about. To me, it’s really cool because the photic sneeze reflex is a pseudo-scientific observation a friend and I made in elementary school that has real backing in molecular and cellular neurobiology, the field that I now study in college.