Whether you opt for the handlebar 'stache or the pencil 'stache, there are a few things to know about the 'mo.
Like any other body hair, mustaches likely evolved to protect and keep the skin warm, said Dr. Joshua Zeichner, a dermatologist at the Mount Sinai Hospital in New York.
Biologists at UCLA who studied 129 different primates found that facial hair helped species recognize one another to prevent inbreeding, and was longer in species that lived farther from the equator.
Dr. Angela Christiano, the Columbia University Medical Center dermatologist who made headlines last month for inching closer to a cure for baldness, said people of Asian and African descent tend to have less facial hair than people from Northern Europe, which suggests it has something to do with climate.
However, mustaches and beards aren't as important as eyelash and nose hairs, which keep particles out of the eyes and nose, she said.
"It doesn't seem to have any real function other than gender identification," she said.
But not all men can grow facial hair like the Brawny paper towel man - er, before they changed the label and shaved his little illustrated face.
"A lot of that has to do with genetics," Zeichner said. "Some men just have very sparse beards."
Men develop beards during puberty when their sex hormones, called androgens, stimulate hair production, he said. The thin hairs that look like peach fuzz give way to dark, thick hairs.
Some men continue to develop facial hair well into their college years. But if they don't have the facial hair of their dreams (like Red Sox catcher David Ross' beard, maybe?) by the time they're 30, it's probably not coming.
"I'm sorry to say you may not be getting it," Zeichner said.
But, hey, fewer ingrown hairs, right?