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For all its everyday nature, not much is known about the act of sneezing. But some of what we do know…well, you might not want to know it. From this point forward, proceed at your own risk. And if you do, don’t let this information fall into the wrong hands.

First let’s dispose of some sneezing folklore.

All that “God bless you,” etiquette is optional. Sorry, devil worshipers, the soul doesn’t leave the body during a sneeze. Nor will eyeballs fall out even if the sneezer forcibly holds her eyelids open. Sneezing won’t stop your heart, and if you plug up your nose your head won’t explode (though your eardrums might not appreciate the gesture).

Now for some science. We sneeze to clear our nasal passages of irritants; the number of times a person sneezes in a row is most likely genetic; thinking about sex can make you sneeze; during a sneeze, moisture particles leave the nose at speeds approaching 100 miles per hour; and, a sneeze can propel germ-carrying particles…what?

Yes, thinking about sex can make you sneeze.

With all our knowledge, the exact mechanism of sneezing is still shrouded in mystery. Scientists know it has something to do with the trigeminal nerve, which is responsible for sensation in the face, including the mucous membranes. It’s also the nerve for motor functions such as biting and chewing.

The trigeminal nerve can be stimulated at points other than the nose, causing us to sneeze. When a woman sneezes, for example, while plucking an eyebrow, that’s the trigeminal nerve.

But the relationship between sex and sneezing? The trigeminal nerve gets a definite pass on that.

Evidence of a sex-sneezing link goes back to the 19th century and a young German ear, nose, and throat doctor named Wilhelm Fliess. Fliess was a friend of Freud, but not so much a friend of science. While he did identify a link between sneezing and sex, his explanation eventually became so fanciful even Freud wished he’d never met him.

Mahmood F. Bhutta and Harold Maxwell, two British doctors who wrote about the link in the Journal of the Royal Academy of Medicine,* consider the sneeze-sex link as both real and more common than previously thought. “As this is a problem that does not lead to morbidity and may be seen as embarrassing to discuss it may be under-reported,” they wrote with a touch of British understatement. They did, however, offer a hypothesis that began with two well-known observations; that, for some people, bright light causes sneezing; and, sneezing can be caused by a full stomach.

Bhutta and Maxwell speculated that, of the several explanations of this effect, the one that stood out involved the parasympathetic nervous system. (In case you zoned out in high-school science, the parasympathetic nervous system manages our anti-fight-or-flight responses. It’s scope includes our glands, digestion and, yes, sexual response.)

Within the parasympathetic system, it’s not uncommon for one set of stimuli to produce unexpected responses. In simple terms, you tweak the parasympathetic system in one part, and another, seemingly unrelated, part responds as well. Scientists call this a “sympathetic response,” the euphemism they prefer to “getting its signals crossed.”

Hence, bright light causes one expected response—our pupils contract—and another, unexpected one—the mucous membranes in our nose kick into overdrive, secreting mucous, and causing the body to think the nasal passages are under attack. Out goes the cry. Sneeze. Sneeze.

Or, you think about sex and get an…uh…expected response, plus the parasympathetic system throws in another one—more undesired than unexpected—for free.

Sneezing, that annoying but harmless activity, used to do little more than tag you as a rude and uncaring person when you didn’t cover your nose. Now it can get you into real trouble.

It might be hard to convince yourself that your spouse’s sneezing fit was caused by an allergy, and not by a smile from an attractive person across the room.

And vice versa.

Will we ever find a way to distinguish between a standard sneeze and a sex-infused one?

As Bhutta and Maxwell pointed out, the future for funded research in this area is bleak (unless Masters of Sex gets desperate for a story line in its tenth season). Perhaps the producers of Divorce Court might be persuaded to kick in a few dollars in the name of more equitable judgments (not to mention more competitive programming).

For now, however, the best we can do is recognize that the common sneeze has become—all together now—nothing to sneeze at.