Period Apps Collect More Than They Give Back

Key Takeaways

• A peer-reviewed analysis in The BMJ argues that digital menstrual tracking risks more harm than benefit, and that evidence for its claimed health benefits is weak.
• Google and Flo Health agreed to pay $56 million to settle a class action over sharing menstrual and pregnancy data for advertising. Meta was found liable by a jury in the same case.
• A Mozilla Foundation study of six popular trackers found enormous variation. One stores everything on your device. Another was found sending detailed reproductive health data to a company not named in its privacy policy.
• Which app you choose matters more than whether you track. So does how much you tell it.

Most privacy arguments involve a tradeoff. You hand over data and get something back, and the thing worth arguing about is whether the exchange is worth it.

An analysis published in The BMJ makes a more uncomfortable argument about one widely used category of app. Katharine Lee and colleagues contend that digital menstrual tracking risks creating more harm than benefit, and that the evidence for the benefits side of the exchange is thin.

Meanwhile, court records from the past year show fairly precisely where some of that data went.

The Evidence Case

I'd separate two claims, because they get blurred together and only one of them is really our territory.

The first is about efficacy. The BMJ authors argue that neither menstrual tracking nor cycle syncing, the practice of adjusting diet and exercise by cycle phase, have actually shown to improve health or performance. They point to decades of sports science research finding no overall effect of cycle phase on performance, injury risk, or health, with any effects found described as trivial and highly individualized.

Their sharper point is that even if cycle phase did correspond to meaningful variation in a given person, simple digital tracking tools couldn't reliably predict it.

I'm not in a position to adjudicate the medical literature, and I'd be wary of anyone claiming otherwise after reading a press release. What I can say is that this is externally peer-reviewed, published in a major medical journal, and directly at odds with how these products are marketed.

The authors also list unwanted surveillance and health data privacy among the harms. That part we can check against the record.

What Already Happened to the Data

In September 2025, Google and Flo Health agreed to pay $56 million to settle a class action, according to reporting by Jonathan Stempel for Reuters. Google's share was $48 million, and Flo's was $8 million. Flurry, a now-defunct analytics company, had settled earlier for $3.5 million.

Meta didn't settle. A jury found the company liable in August 2025 after a two-week trial.

The underlying allegation was specific. Users said that between November 2016 and February 2019, Flo shared personal information about their menstrual cycles and pregnancies with those companies, despite promising to keep it confidential. The claim was brought under the California Invasion of Privacy Act, which carries statutory penalties per violation.

Google stated that no data were used for ads and that customers are prohibited from using Google Analytics to collect protected health information. Flo and Google both denied wrongdoing.

Flo had already settled with the US Federal Trade Commission in 2021 over related allegations. The company says those practices ended years ago and that it did not admit wrongdoing.

Whatever each party's position, the record establishes something that doesn't require interpretation: this category of data has already left these apps and gone somewhere users didn't expect.

The Apps Are Not the Same

Here's the part I found most useful, and it complicates any blanket advice.

The Mozilla Foundation examined six popular trackers, with findings reported by Thomas Germain for the BBC in July 2026. The spread between best and worst is enormous.

At one end, Euki was the only app Mozilla recommended without reservations. It keeps health information on your device rather than sending it to a server, requires no account, and includes a decoy feature that displays harmless fake data if someone else picks up your phone.

At the other, Mozilla found Stardust sending detailed reproductive health information, including pregnancy status, birth control, and specific symptoms, to a data company not named in its privacy policy. Stardust says that company functions only as a technical pipeline into its own analytics, can't identify users by name, and is contractually barred from selling the data.

Planned Parenthood's Spot On app presented a different shape of problem. The app itself doesn't track users, but tapping certain features opens Planned Parenthood's website in a browser, and Mozilla found that site shares what kind of care you're looking for, including HIV testing or gender-affirming care, with an analytics company.

Flo and Clue scored relatively well on transparency and user control. Mozilla found neither sharing health data with third parties, though both tell advertising partners when you open the app unless you disable it. The criticism was that both collect considerably more health information than other apps and keep it on their own servers, which Mozilla's analyst noted creates exposure to breaches and legal requests regardless of whether the company ever shares anything.

Both companies reject that framing and say cloud storage is necessary for the service. Both are based in Europe, which complicates US legal requests. Flo offers an Anonymous Mode intended to ensure nobody, including Flo, holds a user's identity and health data together.

Does Inputting Less Actually Help?

I use Flo. I've used it for years, mostly out of habit, and I log the bare minimum. I also use an old personal email address and a fake birthday. No profile picture, no partners connected, and no other unnecessary information. Strictly dates. I have also turned off all possible data sharing requests.

Having gone through the research, I think that helps with one layer and not the others, and it's worth being precise about which.

Logging less does reduce what sits in the health data store. If there's a breach or a legal request, there's less to find. That's real, and on an app that keeps data on its own servers, it's the layer you have most control over.

What it doesn't change is that the app is installed, that an account exists, and that advertising and analytics partners can be told you opened it. Sara Geoghegan of the Electronic Privacy Information Center made this point in the BBC piece: simply revealing that you use a reproductive health app can matter, because it signals to anyone looking that there's data worth asking for.

So minimal input is a reasonable harm-reduction move rather than a solution. The things that do more are choosing an app that stores data locally, turning off the advertising and analytics sharing where the app allows it, and using features like Flo's Anonymous Mode if you stay with a cloud-based service.

None of that is as satisfying as a clean answer. Once sensitive data exists somewhere, the record on what happens to it over time isn’t encouraging, which is the strongest argument for not generating it in the first place.

What I'd Take From This

The BMJ analysis and the Mozilla report point to the same conclusion from different directions.

If a product collects unusually sensitive data, the benefit should be demonstrated rather than asserted, and the protections should match the sensitivity. A peer-reviewed analysis arguing the first condition isn't met makes the second considerably more urgent.

The useful question was never whether to track. People track for real reasons, including ones their doctors suggested. It's in which app you track, how much you tell it, where that information physically sits, and whether anyone has actually shown that what you get back justifies any of it.