At some point during your shaving routine, you might have noticed a weird-looking hair on your chin. Unlike most of your facial hair, this hair seems especially gnarly—it’s probably especially thick—and if you’ve managed to pluck it out, you’ll find that it’s actually multiple smaller hairs, all bound up and emerging from the same pore.

Congratulations: You’ve discovered phenomenon called pili multigemini. It’s when a hair seems to have Siamese-twinned itself, and now two hairs (or even several more) grow from one single follicle.

“The exact cause is not known, though most doctors consider it a developmental defect,” says Jeremy Fenton, M.D., dermatologist at Schweiger Dermatology Group in New York City. “It may be genetic. It may be caused by the papilla of the hair—the base—subdividing within itself to then generate multiple hair shafts, or by multiple hair papillae fusing together.” One last hypothesis is that the germ cells—the “embryos” of the follicles—get reactivated to create multiple shafts.

Regardless of what causes pili multigemini, there are still numerous questions that need answering, so Fenton did us that favor. Here’s his primer on pili multigemini.

Where does pili multigemini get its name?

Fenton: Pili is the plural form of pilus, which is a term derived from Latin, meaning hair. Multigemini refers to the fact that there are multiple hair shafts derived from a single follicle.

Does pili multigemini affect certain people more than others?

Fenton: It’s believed to be most common in the beards of adult men, and it has been reported on the scalps of children. The exact incidence is not known.

Many people consider the condition to be rare, with an incidence of about 2% of the population. However, one study in 2007 showed evidence somewhere on the body of pili multigemini in every person examined, which suggests that it exists to some extent on everybody. The reality is that it's probably more common than we think, because people are only diagnosed with it if it is causing problems.

So those problems are rare. But what might they entail?

Fenton: Right. If somebody is not having any symptoms from this, then it’s not of any concern. For some, however, pili multigemini may lead to folliculitis, which is an inflammation of the hair follicles. This can cause acne-like bumps and pustules, which can sometimes leave behind scarring.

If you pluck these hairs, do they return in multiples?

Fenton: Plucking hairs can damage the base of the follicle and can help reduce the growth of hair shafts; therefore, it may be helpful in destroying that follicle. But laser hair removal would likely be more effective. On a related note, I do not know of any evidence to suggest that plucking a normal hair will lead to multiple hairs returning in its place.

Also, plucking multigemini hairs has been reported as being more painful than regular hairs.

Where on the body can pili multigemini occur?

Fenton: They most commonly occur in the beard area, but it can appear anywhere on the body. One study showed an equal prevalence between men and women.

You mentioned laser removal as one permanent solution. What about electrolysis?

Fenton: Electrolysis—when the hair follicle is destroyed using chemical or heat energy—is more painful and time-consuming than laser removal, but it is sometimes the only option if the hair is blonde or very light in color.

Is there any way to prevent pili multigemini?

Fenton: Because the disorder’s cause isn’t completely understood, there’s also no known means of preventing pili multigemini.