When Heidi Imhof started losing her hair at 42, she also started losing sleep. Ms. Imhof, a lawyer, was afraid that blow-drying her straight dark hair would hasten the shedding, so she got up two hours early to shower and apply mousse and volumizers. When her hair finally air-dried, she’d pull it back, hoping to hide the bald patches on her scalp.

“I was desperate,” she said.

The hair thickening shampoo Nioxin didn’t help. Neither did Rogaine. Then she heard about Harklinikken, a Danish company offering a customized hair extract that’s given only to those who pass a fairly rigorous selection process.

Ms. Imhof, who lives in Land O’Lakes, Fla., was skeptical. The company’s before and after photos seemed too good to be true. But she went for a consultation and made the cut. (Harklinikken’s products are not available to anyone with autoimmune illnesses like alopecia or baldness from scarring, or anyone who is unlikely to see at least a 30 percent increase in growth.)

After three months of applying the $88-a-month serum, Ms. Imhof was so excited by the results that she overcame her embarrassment about the subject and posted her own before-and-after photos on Facebook.

“You can’t see holes in my hair anymore,” she said.

Harklinikken (“hair clinic” in Danish) inspires great loyalty. Four out of five users come as referrals from satisfied customers, said Lars Skjoth, the company’s founder and chief scientist. The results are certainly compelling. After four months of daily application — that is, working the tea-colored tonic into the hair section by section, then letting it sit on the scalp for six hours — most users regain at least 30 percent of lost density, and some as much as 60 percent, according to company figures.

Harklinikken does not advertise, but the 25-year-old multinational company is beginning an aggressive expansion into the $3.6 billion hair-loss market in the United States, meaning you’re likely to hear a lot more about it. A New York clinic opened in June inside the Core Club in Midtown (you don’t need to be a member to get an appointment); and in August, Harklinikken consultations became available at some 70 Women’s Care Florida obstetrics and gynecology clinics. (Roughly 75 percent of the company’s 50,000 active users are female.)

Mr. Skjoth said the plan is to have a presence in every state in the next two years. The company recently opened outposts in Tampa, Fla., and Beverly Hills, Calif.

Panos Vasiloudes, a Tampa dermatologist and Harklinikken’s medical director, said the company has double-blind, placebo-controlled studies it hopes to publish next year in peer-reviewed journals. Such studies are the one thing some dermatologists say they need to recommend the product to patients.

For now, Maryanne Senna, a dermatologist and the director of the Hair Academic Innovative Research Unit at Massachusetts General Hospital in Boston, said the best she can tell patients who ask — and a lot of them do — is that Harklinikken won’t do any harm.

“Don’t get me wrong — I really want it to work,” said Dr. Senna, who also teaches at Harvard Medical School. “There aren’t a lot of options, and I’d love to be able to say to my patients, ‘This is something you can try that is worth the money.’ But I can’t do that yet.”

Harklinikken’s formula, refined over 20 years, is derived from plants and cow’s milk. That’s the most Mr. Skjoth will say about it. In the 1990s, clients mixed it with Rogaine, Mr. Skjoth said, “and then we took the Rogaine part away and started focusing on the actual liquid.”

Small studies have shown the efficacy of various plant-derived ingredients, mostly in mice. But two potential explanations for Harklinikken’s success have little to do with its formula.

One is how much emphasis the company places on compliance, the major stumbling block in the efficacy of any treatment, said Dr. Senna, an author of studies on the subject. Prospective users are questioned about their ability to stick to a regimen because the extract must be applied every day, and they are told that the more conscientious they are, the better. Users are also reminded and encouraged with regular check-ins.

Clients must also use the company’s shampoo, conditioner and styling products, forsaking all others — a psychological as well as a financial buy-in, Dr. Senna said. (Mr. Skjoth, who has a master’s degree in nutrition and chemistry but is not a doctor, said this is because other products may clog the scalp, causing hair loss.)

Hair changes about as fast as grass grows, which is to say it’s extraordinarily slow and not visible to anyone checking impatiently in the mirror every day. But during regular follow-up appointments, Harklinikken uses high-tech equipment to photograph and magnify the scalp and count new hairs and active follicles, which motivates users to adhere to the regimen. Too many people give up on treatments like Rogaine and low-level-light devices before they’ve had a chance to work, Dr. Senna said.

It’s also possible that some of Harklinikken’s users are women whose hair would have grown back even if they’d done nothing. Many women who arrive in a dermatologist’s office with prior diagnoses of female pattern hair loss actually have what’s called telogen effluvium. That’s a period of acute shedding of hair — meaning up to 60 percent of hair — three months after a triggering event like pregnancy, significant weight loss or starting or stopping hormone medications.

“Once that hair has stopped shedding, it does regrow, at a rate of about a centimeter a month,” said Dr. Senna, who suffered from the condition after each of her pregnancies. She shares photos of herself with patients, to show she can sympathize. In one, her entire frontal hairline clearly is growing back in. “If I’d used a treatment, I would have thought it was a miracle drug,” she said.

Users of the extract say that one of the strengths of Harklinikken is that it doesn’t claim to be a miracle.

“It wasn’t: ‘You’re going to get a full head of hair,’” said Jon Centella, 35, of Apollo Beach, Fla., who started seeing peach fuzz after four months. “It was: ‘We’ll give you 30 percent,’ and that’s what made me comfortable enough to give it a shot.”

[“Source-nytimes”]