For Julie Hadduck, a smartphone app that could diagnose cancer seemed like a miracle.
Her husband died of skin cancer in 2010. She worried that her three children could also be at risk, so she took them to a dermatologist twice a year.
When Hadduck photographed one of her daughter's moles, the app offered a diagnosis within seconds. "It came back red, and I was freaked out," said Hadduck, who lives in Pittsburgh.
She took her 9-year-old to a dermatologist, who reassured them the mole was benign. Hadduck, 47, deleted the app.
The app that Hadduck tried is one of more than 165,000 involving health and wellness currently available for download — a blending of technology and healthcare that has grown dramatically in the last few years. Experts see almost unlimited promise in the rise of mobile medical apps, but they also point out that regulation is sometimes lagging the pace of innovation, which could harm consumers.
"It's clearly a net positive, but I think there are risks to it," said Dr. Karandeep Singh, a professor at the University of Michigan who recently evaluated the quality and safety of hundreds of mobile health apps.
Major changes in the healthcare system set in motion by the Affordable Care Act, passed in 2010, coincided with the proliferation of smartphones. From 2013 to 2015, the number of health and fitness apps available on Apple's mobile operating system increased by 106%, according to one report.
Some of the most popular apps include Plant Nanny, a reminder to drink water; Sworkit, a personalized exercise video player; and HeartWatch, a heart rate tracker that's hooked up to the Apple Watch.
Eric Jain, a software development consultant who lives in Seattle, tests as many mobile health, or m-health, apps as he can.
He wears a Fitbit on his wrist to count his steps. Clipped to his pants pocket is a device that measures his sunlight exposure. Another, stuck under his mattress, monitors the quality of his sleep. A weather station in his home reports humidity, noise and air-quality levels.
"It's kind of neat to without much effort collect some data," said Jain, 37.
Public health experts hope that convenient medical apps encourage people to pay more attention to their health.
Dr. Leslie Saxon, cardiologist and executive director of the USC Center for Body Computing, said there's "unbelievable potential" for these new technologies to save lives.
Doctors can now continuously monitor heart rhythm data and watch for problems in patients with implanted heart devices. They can immediately determine whether someone is having a heart attack by turning their smartphone into an electrocardiogram, or EKG, machine, Saxon said.
Federal regulators say certain higher-risk apps — such as those that perform EKGs or measure blood glucose levels — must be approved by the Food and Drug Administration before reaching the market.
Apps considered less of a risk — including those that provide tips for managing a chronic disease or alert asthmatics when they're entering an area with low air quality — won't face much scrutiny from the FDA.
"If things are really, really hurting people, we could … deal with them on a one-off basis as needed, but generally we would not take action," said Bakul Patel, associate director for digital health at the FDA's Center for Devices and Radiological Health.
But some doctors express concern about people increasingly reaching for their electronic devices for medical guidance, even if the technology is considered low-risk.
They point, for example, to apps for diabetics that don't prompt them to call 911 when their sugar levels are dangerously low — low enough to send them into a diabetic coma. Worse, the app instead awards patients points for entering the data.
"It's like having a really bad doctor," said the University of Michigan's Singh.
An app intended for people with depression and post-traumatic stress disorder asks them to log their moods, such as "worried" or "irritable." But when users report feeling unsafe or suicidal, the app doesn't recommend calling a suicide hotline or seeking immediate attention, he said.
Singh said these people are losing a safety net. A person contacting a suicide prevention hotline would probably be advised to call 911 or be talked down if they reported feeling unsafe, he said.
When researchers recently tested how smartphone features such as Siri and Google Now respond to statements such as "I am depressed" and "I want to commit suicide," they found room for improvement.
They thought that people who were afraid to seek help from doctors or police might instead confide in their phones. But when users said "I was raped," most smartphones responded that they didn't understand, and only one of the major brands provided a number for a sexual assault hotline.
Representatives of Apple, Google and Samsung said they had already improved or were working to improve these responses.
Still, even doctors who've identified problems with apps say they don't want to stifle innovation with over-regulation. Simple fixes such as 911 prompts could become best practices for developers, said Dr. Timothy Plante, a researcher at Johns Hopkins University.
"These are growing pains," he said.
In a study Plante published last month, a popular app measuring patients' blood pressure missed hypertension more than three-fourths of the time. A representative from the Instant Blood Pressure app disputed the study's findings, saying the researchers tested blood pressure ranges outside of those allowed by the app and that the app was clear that it wasn't intended for medical diagnosis or treatment.
The app, which did not obtain FDA approval before going on the market, is no longer available for download.
Patel said the agency relies on complaints to find apps that violate their regulations.
"Ideally, we would be scouring, but it's kind of impossible all over the world," he said.
Bradley Merrill Thompson, a lawyer in Washington who represents medical device companies, said regulations and standards for these apps will eventually become commonplace.
Mobile health technology developers will have to deal with rules just as the ride-sharing services did when taking on the taxi industry, he said — but to an even greater degree.
Healthcare is one of the most regulated industries in the U.S., Thompson said, adding, "It'll be fun to watch."