Worried-well online have new symptom to fear

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The next time you use your smartphone to inquire about migraine symptoms or to check out how many calories were in that cheeseburger, there is a chance that information could be passed on to insurance and pharmaceuticals companies.

The top-20 health and wellness apps, including MapMyFitness, WebMD Health and iPeriod, are transmitting information to up to 70 third-party companies, according to Evidon, a web analytics and privacy firm.

(Read more: Got health insurance? Good luck finding a doctor)

Third parties, which consist primarily of advertising and analytics firms, typically use the information gathered from consumers who are tracking diseases, diets, bicycle trip distances and even menstrual cycles to build profiles or display personalized ads.

(Read more: Health care needs a dose of social media)

"You are talking about some of the most sensitive details of your life being widely available to others," said Jeff Chester, executive director of the Center for Digital Democracy, a consumer privacy group. "That information is being sucked up and collected surreptitiously by a host of online companies that are sharing, selling and trading that information."

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Several of the apps, including WebMD, said transmitted information about their users is not personally identifiable and is not being sold.

The app companies also said that the information is typically used for advertising and site analysis on the app, among other purposes. WebMd said it did not allow third-party companies to combine the consumer data collected about its users with other profile information or use it beyond its site.

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Regulations bar the tracking and selling of individuals' specific medical and prescription records. Yet some companies are figuring out ways around those restrictions by building digital health profiles about people based on their use of the web and mobile apps.

Health apps have proliferated in recent years, with both the Apple and Google stores offering several hundred for download. In exchange for providing the apps for free, executives said that the companies were likely to make money by selling ads or data.

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"If there is a lot of content that is being provided to you for free, data are driving the economy of that content," said Scott Meyer, chief executive of Evidon, noting that tracking and selling of data tied to mobile apps remains far less sophisticated than that of the web but is quickly moving ahead.

As the numbers and use of health apps have grown, many founders are predicting a phase of consolidation, with health insurance and pharmaceuticals companies among the most enthusiastic buyers.