Walgreens expects to reach about half the country by the end of the year with a new telemedicine service that lets people see doctors for minor ailments without leaving the home or office.

The nation's largest drugstore chain is expanding a smartphone application it started testing last December to tablets and personal computers and plans to make it available in 25 states. The growth comes as major insurers UnitedHealth Group and Anthem prepare to expand their own non-emergency telemedicine services to about 40 million more people by next year.

Doctors have used video feeds and other technology for years to treat patients in remote locations. But experts say growing smartphone use and customer demand are fueling a rapid expansion of telemedicine into everyday care the family doctor used to handle.

The American Telemedicine Association estimates that about 450,000 patients will see a doctor through a secure Internet connection this year for a primary care consultation. That's a slice of the roughly 15 million people who will have care delivered by telemedicine, but the primary care portion has probably doubled over the past couple years, said Jon Linkous, CEO of the nonprofit association, which advocates for telemedicine.

"I would say without a doubt it's the fastest area of growth in telemedicine," he said. "There's this convenience factor that makes it so compelling to consumers."

Drugstores, grocers and big retailers like Wal-Mart have been opening clinics inside their stores for years now, giving patients several less-expensive alternatives to a doctor's office when they need help. The telemedicine apps aim to offer even more convenience by providing care wherever the patient is located.

Programs offered by Walgreens Boots Alliance Inc. and the insurers give customers around-the-clock access to doctors who can then diagnose and treat conditions like allergies, a sinus infection or pink eye that don't require a physical exam.

The nation's largest health insurer, UnitedHealth Group Inc., started covering earlier this year telemedicine visits for about a million people with employer-sponsored health plans and expects to expand that to 20 million customers next year. Likewise, the Blue Cross-Blue Shield insurer Anthem Inc. started its LiveHealth Online service in 2013 by offering it to a few thousand people.

It now provides the service in 44 states and also expects 20 million of its customers to have access by next year.

Doctors say telemedicine can help improve access to care for many patients, as long as the care is good, a record of the patient visit makes it back to that person's regular doctor and safety isn't compromised.

Walgreens said the doctors in its program are trained to quickly determine whether a patient needs more care than they can provide during a virtual visit.

"We're very careful in only using telemedicine for certain conditions that are amenable to this," Walgreens Chief Medical Officer Dr. Harry Leider said. "We're not treating heart attacks."