A few months ago I was sitting at my desk when one of my coworkers called over to me: "You know you do that every day at this time?"
I looked at the clock. It was 4:30 in the afternoon. I was a little confused. Was she calling me out for my Twitter or Facebook habit? I checked, and I didn't have those tabs open. I tend to snack a lot at my desk—was I chewing super loudly? Now I was a little paranoid.
"Do what?" I asked.
"Sneeze," she said.
It took me a second to realize that I had, in fact, just sneezed—at least four times. This is something that happens so often I don't even notice it anymore, and I certainly never thought about what time it was. I've always been a big sneezer, and I've always thought of it as a quirk, rather than an issue. I'll be minding my business, a brief sneeze attack would hit, and then I go about my day.
It wasn't until my coworker pointed it out that I thought to look for a pattern. The next day when I sneezed, it caught my attention. I looked at the clock: 3:45. I made eye contact with my coworker and we both laughed. Then it happened again the next day at 4:33, and the next around 4:45. It's become a bit of a game in my office—if I sneeze in the morning, it's an omen that the day might be thrown off. If it happens late in the afternoon, all is well.
As it turns out, this is actually a thing. There are dozens of threads on Reddit, Yahoo Answers, Quora, and other forums started by people hoping to find out why they sneeze every morning around 8:00, or every day after they eat lunch. Some say attacks of 10 to 15 sneezes hit them just as they're going to sleep, while others are afflicted at precise times in the afternoon, like me. Some say they have other allergies, while others aren't prone to that problem.
One common explanation from doctors—and people in forums who say they are doctors—is that we may be exposing ourselves to specific irritants at around the same time every day. Maybe we walk outside every morning and pollen gets up our noses, or we are always in a particularly dusty room at 4:00 pm. I, for better or worse, tend to spend almost the entire day at my desk, so unless an irritant is traveling to me every afternoon, I'm not sure that explanation pertains to me.
Amanda Parvis-Lanzo, a television producer in Connecticut, says she just started noticing this phenomenon herself, and she suspects it's food-related. "It typically happens after a meal," she says.
Bill Clark, a tennis coach in Ft. Lauderdale, Florida, says he experiences significant sneezing—up to 20 times in a row—after dinner, especially when he's very full. "It's been happening since I was around 20 years old," he tells me. "I'm 61 now."
The jury's out on whether eating or fullness can cause one to sneeze, though several papers have described an apparent inherited predisposition to this kind of sneezing. In general, there's been very little research into this phenomenon. One of the most popular suggestions from the research community, however, is that our nasal mucus, like other parts of our body, operates according to a circadian clock.
"Circadian rhythm" is the term we use to describe the cycle our bodies (and the bodies of many animals) go through in a 24-hour period. They manifest in changes of brain wave activity and hormone production, as well as things like feeling hungry and sleepy. They're partly innate, and partly determined by external factors like sunlight and temperature. If you've ever had a cold that seemed to get worse early in the morning and at night, it may not surprise you that most tissues, including those in the nose, appear to have their own circadian "clocks."
A 2015 study by a group of Japanese researchers published in the journal Endocrinology may provide some more clues. The researchers found that certain external factors can change those innate rhythms. By giving corticosteroids, a class of steroid hormones, to mice with hay fever whose symptoms were worst in the morning and early evening, they were able to "reset the nasal circadian clock," bringing a better understanding of how these symptoms change throughout the day, and what effect external factors may have. This research might help explain the mechanisms behind circadian rhythms, including, perhaps, the process that makes certain people sneeze every day like clockwork.
But what about humans with no hay fever or known allergies?
Arthur Grant, director of the Comprehensive Epilepsy Center at SUNY Downstate Medical Center, attempted to answer this question when he was in medical school at Case Western Reserve University in Cleveland in 1990. He and a fellow student noticed that another classmate seemed to sneeze—loudly—at around the same time during class every morning.
The sneezes were also notable because there seemed to be no obvious cause. No one else was sneezing, the sneezing student didn't have any known medical conditions or allergies, she wasn't on any medication, and she was never looking up at the lights or out the window at the sun when it happened, ruling out the "photic sneeze reflex" we've all likely experienced. "On a lark," Grant and his co-author, Eric Roter, decided to test their hypothesis, marking down every time their classmate sneezed during their four hours of class each day. They submitted a paper on their findings to the journal Neurology that was published a few years later.
They recorded 118 sneezes on 69 days, and found that their subject sneezed "with startling regularity" around 8:20 am each day. The paper aimed to answer whether the classmate's sneezes were in fact a circadian phenomenon. Their conclusion? Probably.
"Other things besides the endocrine system have predictable variability throughout the day, so it's also conceivable that the same is true of nasal discharge or moisture or dryness of nasal mucosa, the lining inside the nose," says Grant. "Maybe for some reason she and you and whoever else has this just at a certain time of day, their physiology gets to some threshold where it's irritating and makes them sneeze."
Little headway seems to have been made in the 23 years since, though chronobiologists who focus on the cycles and rhythms of life are regularly making strides toward treatments for issues like insomnia and non-24 sleep disorder (often experienced by the blind) that take advantage of circadian processes.
In the meantime, those of us who can set our watches by our sneeze attacks will have to settle for embracing our circadian quirks.
Update 3/16/17: A previous version of this article states that "everyone" experiences photic sneezes, but only 18-35 percent of people are most likely to experience it regularly.