NEW YORK CITY — The thick, flowing beards adorning hipsters from Williamsburg to Park Slope are driving follicly-challenged New Yorkers to a little-known but growing field of plastic surgery — facial hair transplants.

Whether they're filling in a few gaps or doing a complete beard construction, New York City doctors who specialize in the procedure said they're seeing a growing number of men paying as much as $7,000 to pump up their beards.

"Whether you are talking about the Brooklyn hipster or the advertising executive, the look is definitely to have a bit of facial hair," said Dr. Jeffrey Epstein, a facial plastic surgeon who has performed the procedure for 12 years.

Epstein said he started out doing just a handful of beard transplants each year a decade ago — but is now averaging about three beard implants a week through his offices in Midtown East and Miami.

Dr. Yael Halaas, another plastic surgeon who specializes in facial hair transplants, said an increasing number of "hip" and "fashionable" young professionals in their 20s and 30s are seeking the procedure.

"I get a lot of detail-oriented people — artists, architects," the doctor said, noting that beard-centric neighborhoods such as Williamsburg, Bushwick and Park Slope have each delivered four to five clients to her practice in the past year.

In addition to beardless hipsters, doctors said their clients include men who have struggled since adolescence to grow a beard, those undergoing a gender transition from female to male, men with with facial scarring and Hasidic Jews who hope to achieve denser payot, or sidelocks. A greater awareness of facial hair transplants has also fueled the popularity of the procedure, doctors said.

A 39-year-old New Yorker who works in the catering industry said he got a beard transplant in April 2013 to help him feel younger.

"I couldn't believe how much I had changed over the years and that I no longer looked like myself," he wrote by email on the condition of anonymity.

The man said his beard had thinned out as he aged. The beard transplant let him play with all types of looks, from fully bearded to scruffy to clean-shaven.

"I had contemplated [getting a beard transplant] for approximately eight months," he said, "Knowing the results, I wish I hadn't wasted so much time deciding."

The hair for beard transplants typically is taken from the patient's head — roots and all — and then planted through micro-incisions on a bare patch of face, in an eight-hour procedure under local anesthesia, similar to how hair transplants are done, doctors said.

The procedure ranges in price from $3,000 for fill-ins of beard sections to $7,000 for a full beard, doctors said.

While doctors prefer head hair, on rare occasions patients who are balding might be able to use hair from the chest for the surgery, doctors said.

"If they are balding, they might need that extra hair for their heads," said Dr. Glenn Charles, who is based in Florida but said 30 percent of his clients are from the New York City area.

Once transplanted, the beard hair takes root gradually. The hair then falls out, but the roots stay and begin to grow new hair within several months, doctors said.

Once it's fully healed, the new beard can be shaved regularly and will grow back just like real hair.

Surgeons said they are often approached by patients with images of how they want to look.

"They may bring in a picture of an actor or a model," Charles said. He named George Clooney and Ryan Gosling as repeat facial hair role models.

The Brad Pitt scruff is a common request of Epstein, and occasionally the Tom Selleck moustache.

Peter, a 46-year-old who asked that only his first name be used, had his beard filled out by Epstein 10 years ago. He described the change in appearance as a gradual process.

"It wasn't like 'Wow. What happened to you?' like one day...you dyed your hair," Peter said. "Nobody really noticed. It is not a drastic change."

Peter didn't present Epstein with a photo, but instead worked with the doctor to produce an individualized look for a fuller beard.

"Sometimes I am clean-shaven or it's more scruff and sometimes I let it grow out," Peter said. "At least I have choices, right?"