The body has a tendency to sprout hair in many strange places: Ears, noses, knuckles. For those afflicted with a rare type of tumor dubbed a limbal dermoid, it can even grow out of an eyeball.

But few follicles cause as much stress as a synophrys, the medical term for the unibrow—hair in the center of the forehead that creates the impression of a single, unified, stern-looking eyebrow.

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Waxing, laser treatments, or just old-fashioned shaving can alleviate symptoms. But if you’re curious what actually causes it, you’ll need to turn to your DNA. According to a recent study published in Nature Communications, an investigation of more than 6000 subjects yielded specific genes that were associated with hair density, greying, curling, and brow fusion. Unibrows were found in people (specifically, men) with the gene dubbed PAX3. The paper’s authors theorized that once a feature has been isolated to a specific gene, the cosmetics industry may one day come up with a product that can inhibit or alter its behavior.

That assumes you would want to. While unibrows aren’t the style of choice in the United States, the Asian nation of Tajikistan considers it to be a trademark of beauty. Women lacking in PAX3 use a green herb called usma to fake it, creating a solid line of brow.