Period Tracker Privacy: Study Reveals Which Menstrual Apps Protect User Data

Period Tracker Privacy has come under renewed scrutiny after a new study found that several popular menstrual tracking apps collect and share user data in ways that may raise privacy concerns, while others offer stronger protections for sensitive health information.

The Mozilla Foundation examined six widely used period-tracking apps—Flo, Clue, Stardust, Spot On, Period Calendar and Euki—to assess how they collect, store and share reproductive health data.

The report found significant differences in privacy practices. While some apps offer robust safeguards, others share user information with analytics and advertising partners, including Google, Meta, Microsoft, TikTok and several data management companies.

Researchers identified Stardust as the only app in the study that shared detailed reproductive health information with an external data management service. According to Mozilla, the app transmitted information such as pregnancy status, birth control use, mood, alcohol consumption and menstrual symptoms to RudderStack, a company not listed in Stardust’s privacy policy.

Stardust said it uses RudderStack only as a technical service to transfer data into its own analytics systems. The company said the information does not identify individual users and that contractual agreements prevent RudderStack from storing or using the data for its own purposes.

Mozilla also highlighted concerns involving Spot On, an app developed by Planned Parenthood. Although the app itself does not share health information, researchers found that some features redirect users to Planned Parenthood’s website, where analytics tools collect information about healthcare searches, including HIV testing and gender-affirming care.

The study also found that several apps share device identifiers and usage data with advertising and analytics companies. While this information does not include medical records, privacy experts warned that revealing someone’s use of a reproductive health app could still expose sensitive personal information.

Mozilla identified Euki as the strongest privacy-focused app in the review. Unlike other platforms, Euki stores reproductive health data only on the user’s device and does not require users to create an account. The app also includes a decoy mode that displays harmless information if someone attempts to access the device without permission.

Researchers also gave positive ratings to Flo and Clue for providing transparent privacy controls and allowing users to disable advertising and analytics tracking. However, Mozilla noted that both companies store health information on their own cloud servers rather than exclusively on users’ devices.

Both companies defended their practices, saying cloud storage supports core app features while strong encryption and security measures protect user information. Flo also pointed to its Anonymous Mode, which separates personal identity from health records, while Clue said it has never shared private health data with government authorities.

The report also reviewed each company’s privacy history. Mozilla noted that Flo settled a US Federal Trade Commission case in 2021 over allegations that it shared sensitive user information with third parties after promising to keep it private. Flo said it resolved the matter without admitting wrongdoing and has significantly strengthened its privacy protections.

Privacy advocates said the findings have become increasingly important since the US Supreme Court overturned federal abortion protections in 2022, raising concerns that authorities could seek reproductive health data during criminal investigations.

Experts urged users to review an app’s privacy policies, understand where their data is stored and determine whether they can disable tracking before choosing a period-tracking service.