Most doctors have a license to practice medicine in just one state. Lindsey Mcilvena can practice in 26.

"I've lost track a little bit," she said of all her licenses.

Mcilvena is a telemedicine doctor, one of a growing number who prefer to treat patients remotely, from the comfort of their own homes. They connect with patients by video chat, or through apps where patients can use their smartphone to talk to a doctor about a cold or a prescription.

For Mcilvena, 35, it began as a side gig. She was fresh out of medical school, running her own practice in Encinitas, Calif. She started to take telemedicine appointments to help pay the bills as she expanded her brick-and-mortar practice. But she liked it so much that in 2015 she made the leap to practicing remotely full time.

She now works full-time for the telemedicine startup HeyDoctor, which allows her to treat patients while spending time with her 16-month-old son. "I was a fan for the flexibility, for being able to work from home and set my own hours," she said. "Those things don't apply to very many medical positions."

Telemedicine is still, by most accounts, a niche occupation. A study published in December in the academic journal Health Affairs combed 2016 survey results from the American Medical Association to find that only 15.4 percent of physicians worked in practices using telemedicine.

But that may soon change. Long heralded by the medical community for its potential to make health care more accessible and efficient, telemedicine now seems poised to go mainstream — and raise new questions about how medicine practiced through an app compares to a doctor's office visit.

Private health plans, Medicare, most state Medicaid programs, and the U.S. Department of Veterans Affairs cover some virtual doctor's visits. More than 35 states and the District of Columbia have laws requiring private insurance companies to reimburse providers for care delivered remotely. The American Medical Association supports telemedicine so long as it's "consistent with related in-person services."

In telemedicine, tech-savvy doctors who are good communicators are the ones who thrive. It has led to a boom in well-funded telehealth startups like HeyDoctor, Roman and Hims, the Viagra-selling company valued at $1 billion in January.

For some physicians, especially younger ones who grew up doing almost everything online, telemedicine is no longer a side gig: It's a career goal.

"American medicine is not great," said HeyDoctor CEO Brendan Levy, who is licensed in 30 states. "You spend a lot of time just doing paperwork and talking about insurance. You spend the same 15 minutes if someone has a cold as you do if you've got a new diagnosis of cancer. It's not a great way to spend the patient's time or your time as a doctor."

Many of the conditions for which people go to a primary care doctor, he said, can be treated through an app.

Ateev Mehrotra, a doctor and professor at Harvard Medical School agreed that telemedicine is great for things like mental health or urgent care. Where that gets trickier, he said, is when someone's condition requires a physical examination, such as a urinary tract infection or strep throat.

"A number of randomized, controlled trials have demonstrated telemedicine is equivalent to face-to-face treatment," Mehrotra said. "Telemedicine is designed to be quick and transactional, but that becomes more complicated when you get into things like testing someone."

Michelle Davey, CEO of Enzyme Health, said the company has found that a doctor's great bedside manner doesn't always translate into a great "webside" manner. She said the company sees doctors fresh out of med school, as well as older physicians who want to partly retire.