A Mozilla Foundation investigation has exposed major differences in how popular period trackers protect sensitive reproductive health information.
Researchers tested Flo, Clue, Stardust, Spot On, Period Calendar and Euki using network analysis and hands-on reviews. Scores ranged from 10 out of 10 for Euki to two for Stardust. Mozilla said the findings carry greater importance after federal abortion protections ended in the United States in 2022.
Stardust Shared Detailed Health Information
Stardust tells users, “Your data is private. Period.” However, Mozilla found that the app sent detailed health information to RudderStack, a provider not named in its privacy policy.
The data included pregnancy status, birth control, moods, alcohol use and symptoms such as stomach cramps and tender breasts. Stardust said RudderStack acts only as a “technical pipeline” and receives no names or contact details.
“Additionally, RudderStack is contractually prohibited from selling or using it for its own purposes,” a Stardust spokesperson said.
Mozilla found a separate problem involving Planned Parenthood’s Spot On. The app’s core tracking features did not share health data. However, its provider search and Roo chatbot opened Planned Parenthood webpages where outside tracking began.
Those pages shared care searches with AB Tasty, including queries for HIV testing and gender-affirming care. “Someone could probably fix this in an afternoon,” Mozilla researcher Shoshana Wodinsky said.
Advertising Trackers Still See App Use
Period Calendar did not transmit logged cycle details during Mozilla’s tests. However, it sent device identifiers and technical information to Google, InMobi and advertising systems without a clear off switch.
Stardust shared similar usage data with Meta and AppsFlyer, although phone settings could reduce some tracking. Spot On’s linked webpages also activated services from Google, Microsoft, TikTok and Pinterest.
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“Data collected from a period tracking app can be part of a whole tapestry woven from many different threads of surveillance,” said privacy advocate Sara Geoghegan. “That can be very revealing.”
Such information may show advertisers, data companies or authorities that someone uses a reproductive health app, even without revealing exact symptoms.
Euki Earns Top Privacy Rating
Mozilla described Euki’s default setup as “squeaky clean.” The app stores health information on the user’s device, requires no account and offers PIN, automatic deletion and decoy-screen features.
Flo and Clue also performed relatively well. Mozilla found no evidence that either shared health information with advertising partners. Both store extensive records on company servers, but users can disable several advertising and analytics connections.
Flo also provides an Anonymous Mode that separates identifying details from health data. Clue gives users separate controls for research, analytics, advertising and personalisation.
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Flo’s past remains relevant. In 2021, the US Federal Trade Commission finalised a settlement over allegations that it shared sensitive information with Facebook, Google and other firms despite earlier privacy promises.
Mozilla advised users to check data storage, third-party access, privacy controls and a company’s track record before choosing a period tracker.
