A Story Many Users Can Relate To
You download a period-tracking app because it promises privacy.
You enter details about your cycle, symptoms, and health, believing that information stays between you and the app. Then a trusted privacy organization publishes findings that challenge those promises.
That’s exactly why the Mozilla Report has become one of the biggest digital privacy stories of July 2026. Mozilla’s investigation claims that the Stardust period-tracking app transmitted sensitive reproductive health information to third-party services by default, raising new questions about how health apps handle personal data.
This article explains what Mozilla discovered, what information was reportedly shared, how Stardust responded, and what these findings mean if you use a period-tracking app.
You’ll also learn how Stardust compares with privacy-focused alternatives and what practical steps you can take to better protect your reproductive health data.
AI Overview
Mozilla Foundation’s July 2026 privacy review found that the Stardust period-tracking app sent sensitive reproductive health information to third-party services during normal use.
Researchers observed data being shared with RudderStack, while device and usage information was also transmitted to Meta and AppsFlyer. Mozilla gave Stardust a 2/10 privacy score and said users have no clear in-app option to completely disable this data sharing.
Key Takeaways
- Mozilla published its Stardust privacy review on July 15, 2026.
- Stardust received a 2/10 privacy rating.
- Researchers observed health data being sent to RudderStack.
- Meta and AppsFlyer also received certain device and usage information.
- Mozilla says the sharing happens by default.
- Stardust says RudderStack cannot use or sell the data for its own purposes.
What did the Mozilla Report find?
Mozilla found that the Stardust period-tracking app transmitted sensitive reproductive health information, including birth control details, symptoms, reproductive goals, and birthdate, to the analytics platform RudderStack. Researchers also observed device and usage data being shared with Meta and AppsFlyer.
What Is the Mozilla Report?
The Mozilla Report is a privacy investigation published by the Mozilla Foundation on July 15, 2026.
Instead of reviewing only Stardust’s privacy policy, Mozilla tested how the app behaved during normal use by monitoring its network traffic.
That approach allowed researchers to see what information actually left the device and where it was sent.
Why Was Stardust Investigated?
Stardust became popular after the 2022 Dobbs decision because it promoted itself as a privacy-focused period tracker.
Many users downloaded the app believing it offered stronger protection for reproductive health information than competing apps.
Mozilla wanted to verify whether those privacy claims matched the app’s real-world behavior.
What Did Mozilla Find?
Mozilla researcher Shoshana Wodinsky analyzed the app while performing everyday actions, such as logging symptoms and updating health information.
Researchers observed multiple data transfers to outside companies during these normal activities.
Mozilla concluded that this wasn’t an isolated event. According to its testing, the sharing occurred automatically as part of the app’s standard operation.
What Data Was Reportedly Shared?
Mozilla says the app transmitted several categories of reproductive health information.
These reportedly included:
| Data Type | Reported Recipient |
| Birthdate | RudderStack |
| Birth control method | RudderStack |
| Reproductive goals | RudderStack |
| Logged symptoms | RudderStack |
| Persistent user ID | RudderStack |
Mozilla also observed device information and advertising identifiers being shared with Meta and AppsFlyer for analytics and attribution purposes.
Why Does This Matter?
Health information is among the most sensitive personal data you can store on a mobile app.
Even when information isn’t attached to your name, a persistent user ID can still increase privacy risks if combined with other datasets.
That’s why Mozilla argues users deserve greater transparency and clearer controls over how their reproductive health information is handled.
How Mozilla Conducted the Investigation
Mozilla didn’t rely only on Stardust’s privacy policy.
Instead, researchers monitored the app’s network traffic while using it normally, including logging symptoms and updating health information.
This method shows exactly what data leaves the device and which external services receive it.
Which Companies Received the Data?
Mozilla identified three main recipients.
| Company | Reported Purpose |
| RudderStack | Data routing and analytics |
| Meta | Advertising measurement |
| AppsFlyer | Marketing attribution |
Mozilla says these data transfers occurred automatically during normal app activity.
Why Is RudderStack Important?
Most users have never heard of RudderStack.
It’s a customer data platform that helps apps collect and route information to analytics and marketing tools.
Mozilla’s concern isn’t that RudderStack is illegal. It’s that sensitive reproductive health information was reportedly sent there in the first place.
Was the Data Anonymous?
Not completely.
Mozilla says the shared information was linked to a persistent user ID instead of a person’s name.
However, privacy experts and the FTC have long warned that unique identifiers can still be linked back to individuals when combined with other information.
Stardust’s Response
After the report, Stardust defended its privacy practices.
The company said RudderStack is contractually prohibited from selling or using customer data for its own purposes.
Stardust also stated it has never received a law-enforcement request for user data.
Mozilla noted that these statements do not change its technical finding that information was transmitted outside the app.
How Did Stardust Get Here?
Stardust became widely known after the 2022 Dobbs decision.
It marketed itself as a privacy-first period tracker at a time when many users were worried about reproductive health data.
Earlier reporting also questioned the app’s claims about end-to-end encryption, leading the company to revise its messaging over time.
Timeline of the Privacy Controversy
| Date | Event |
| 2022 | Stardust gains popularity after Dobbs. |
| 2022 | Encryption claims receive criticism. |
| 2022–2025 | Privacy researchers continue reviewing the app. |
| May 2026 | Privacy policy updated to disclose more partners. |
| July 15, 2026 | Mozilla publishes its 2/10 privacy review. |
| July 16–19, 2026 | Tech media worldwide reports the findings. |
What Makes This Different From Other Privacy Stories?
Many apps collect analytics.
Mozilla’s report stands out because it says sensitive reproductive health information, not just app usage, was transmitted during normal use.
That distinction explains why the findings received widespread attention across the technology and digital privacy community.
Stardust vs Privacy-Focused Alternatives
Mozilla reviewed six period-tracking apps.
Among them, Euki received the strongest privacy recommendation because its core features reportedly keep health data on the device without third-party analytics.
| Feature | Stardust | Euki |
| Third-party analytics | Yes (reported by Mozilla) | Not in core features |
| Privacy score | 2/10 | Recommended by Mozilla |
| Health data sharing | Reported | Not observed in core functions |
| Privacy focus | Yes (marketing) | Yes (technical design) |
Should You Stop Using Stardust?
There isn’t a single answer.
If reproductive health privacy is especially important to you, Mozilla’s findings are worth considering before continuing to use the app.
If you already use Stardust, reviewing its latest privacy policy and understanding what information you share is a sensible first step.
Who Should Consider an Alternative?
You may want to switch if you:
- Prefer apps with minimal third-party analytics.
- Track highly sensitive reproductive information.
- Want stronger privacy protections.
- Live where reproductive health data may have legal implications.
Mozilla specifically highlighted Euki as a stronger privacy-focused option.
Practical Steps to Protect Your Health Data
Regardless of which app you use, these habits improve your privacy.
1. Read the Privacy Policy
Check whether the app shares data with analytics or advertising partners.
Many users skip this step, but it explains how information may be processed.
2. Limit Shared Information
Only record information you truly need.
Less stored data generally means less information that could potentially be shared.
3. Review App Permissions
Disable permissions that aren’t necessary.
Also review privacy settings after major app updates.
4. Keep Your Apps Updated
Developers often improve privacy and security through updates.
Installing the latest version helps you benefit from those changes.
Common Mistakes Users Make
Many people unintentionally weaken their privacy by:
- Trusting marketing claims without checking privacy practices.
- Never reading privacy policies.
- Assuming “anonymous” always means impossible to identify.
- Ignoring app permission settings.
- Using outdated app versions.
What This Means for the Health App Industry
The Mozilla Report goes beyond one app.
It highlights how users increasingly expect health apps to match their privacy promises with transparent technical practices.
Future privacy reviews are likely to place greater attention on how sensitive health information is collected, processed, and shared.
Looking Ahead
Privacy experts expect more scrutiny of health apps over the next few years.
Possible changes include fewer third-party analytics tools, more on-device processing, and clearer consent controls before sensitive data is shared.
Mozilla is also expected to continue expanding its privacy reviews to additional wellness and reproductive health apps.
Practical Application: How to Choose a Privacy-Friendly Health App
If this report made you question the apps on your phone, use this checklist before installing another one.
Check the Privacy Policy
See whether the app clearly explains:
- What data it collects
- Who receives the data
- Why it is shared
If these answers are vague, think twice.
Look for Third-Party Analytics
Many apps use analytics.
The important question is whether sensitive health information is included in those analytics.
Mozilla’s investigation focused on this distinction.
Review Privacy Controls
A trustworthy app should let you control your data.
Look for options to:
- Delete your account
- Export your data
- Disable analytics where possible
- Remove stored information
Research Independent Reviews
Don’t rely only on App Store ratings.
Independent privacy reviews from organizations like Mozilla often reveal technical details that ordinary users cannot see.
Expert Take
The biggest lesson isn’t that every period tracker is unsafe.
It’s that privacy claims should always be backed by technical evidence.
Mozilla’s investigation reminds users that marketing slogans and actual data practices aren’t always the same thing.
Conclusion
At the beginning of this article, we imagined downloading a health app simply because it promised privacy.
The Mozilla Report shows why many users are now asking tougher questions about those promises.
Mozilla’s testing found that Stardust transmitted sensitive reproductive health information to third-party services during normal use, while the company maintains that its partners cannot use the data for their own purposes. Those two facts can exist at the same time, which is why transparency matters.
Whether you continue using Stardust or choose another app, understanding how your health information is handled is becoming just as important as the features the app offers.
Sometimes the most valuable privacy setting is simply knowing what questions to ask.
Frequently Asked Questions
What did the Mozilla Report find about Stardust?
Mozilla found that Stardust transmitted reproductive health information, including birthdate, birth-control method, reproductive goals, and symptoms, to RudderStack during testing. It also observed device and usage information being shared with Meta and AppsFlyer.
Is Stardust selling user data?
Mozilla’s report did not conclude that Stardust sells data to brokers.
Stardust stated that RudderStack is contractually prohibited from selling or using customer data for its own purposes. Mozilla’s concern focused on the transmission of sensitive information to third-party services.
Is a unique user ID anonymous?
Not necessarily.
Mozilla notes that a persistent identifier can still be linked to an individual when combined with other available information, even if it doesn’t include a person’s name.
Which period tracker did Mozilla recommend?
Among the apps it reviewed, Mozilla highlighted Euki as its strongest privacy recommendation because its core features reportedly keep health data on the device without third-party analytics.
Should I delete the Stardust app?
That depends on your personal privacy expectations and risk tolerance.
If protecting reproductive health data is a top priority, reviewing Mozilla’s findings and comparing privacy-focused alternatives can help you make an informed decision.
