https://www.sciencedaily.com/releases/2018/07/180705114014.htm

Of 14 diary apps analyzed, all collected medical information from the user with 57% (8/14) offering the capability to store patient diary data on the app providers' servers, 14% (2/14) not providing clear statements as to whether patient data would be stored locally or remotely, and others storing data locally on the user's device and/or in Dropbox's "cloud."

"In 2018, it is estimated that nearly half of 3.4 billion smartphone users will use health-related apps, and currently, there are a wide range of apps on the market for various neurologic and pain conditions," said lead author Dr. Mia Minen, of NYU Langone Medical Center, in New York. "We think our study may have widespread implications for people suffering from various chronic conditions."