You’re lethargic. Overcome with ravenous hunger. And if anyone in your path does something even remotely irritating? Let’s just say that you might not react with your usual patience. You glance at your phone and a notification glows on the screen: your period tracking app is reminding you that, yes, you’re in the luteal phase. Suddenly it all makes sense.
Millions of women around the world are using apps to track and make sense of their menstrual cycle; some of them will turn to these platforms to discover when they are most fertile, to try to conceive. One 2024 study estimated that downloads for three popular apps – Clue, Flo and Period Tracker – have surpassed 250 million. They’ve become a handy way for users to record and keep tabs on changes to their mood or any physical symptoms throughout the month.
It is hardly surprising that women are keen to find ways to arm themselves with as much information about their cycle as possible. Menstrual health, and women’s health overall, remain under-researched and underfunded. It tends to take two years to be diagnosed with polycystic ovary syndrome (PCOS) and between seven and nine years to get diagnosed with endometriosis; both conditions significantly impact the menstrual cycle. Anecdotally, at least, phrases like “it’s just your hormones” can still be all too common refrains when you raise issues with a doctor.
Period tracking apps seem to offer a way, then, for women to know what’s going on inside their own bodies. Dr Stefanie Felsberger is a research associate at the University of Cambridge’s Minderoo Centre for Technology and Democracy, and the lead author of a recent report, “The High Stakes of Tracking Menstruation”. “The apps become a space where a lot of people negotiate their feelings of frustration, or their feelings of not having control over what is happening [to them],” she says. “They become a tool to manage and live with your cycle.”
For those who’ve struggled with their mental health, for example, it can be reassuring to be able to pinpoint a bout of low mood to the luteal phase, which comes between ovulation and menstruation. And it can be validating to be able to show your doctor months’ worth of data.
But the advantages of cycle tracking can blind us to the realities of what is happening to our health information: as Felsberger puts it, the benefits can feel “very immediate, but the harms feel really abstract”. Who hasn’t been guilty of scrolling past pages of tiny text, then ticking “agree” without questioning where our information is going, and how it might be used? “When you’re looking for a menstrual tracker, you’re looking for something that can help you understand [your cycle] better or find patterns,” says Felsberger. You might be stressed out, fed up and desperate for answers; and so “the question of data privacy”, she adds, “is never part of that process” of selection.
But perhaps it should be. As Felsberger writes in her report, cycle tracking apps can “transform personal health information into data points to be collected, analysed and sold”. Essentially, if your app is free, then the company may well be trying to make money from your data. Many apps include software development kits, or SDKs, for advertising, which allow developers to monetise platforms with in-app ads or to exchange data with third parties. The data advertising “ecosystem”, Felsberger explains, leans heavily on “these trackers that are built into the apps and into websites, that automatically share data” with other companies, often to use for targeted ads.
If you’ve ever wondered why your social media feed is filled with links to products and brands you’ve vaguely expressed an interest in, then you’ve experienced targeted ads. These ads might be tailored to your location, age or gender. In ex-Facebook employee Sarah Wynn-Williams’s book Careless People, she alleges that the company tracked when teenage girls deleted selfies, “so it can serve a beauty ad to them at that moment”, when they might be feeling vulnerable (Facebook has previously denied targeting users based on their emotional state).
Research from Privacy International and the internet non-profit Mozilla found that multiple period apps have shared information with third parties, including advertisers and data brokers. In Privacy International’s 2019 report, 63 per cent of the 36 apps they investigated had automatically transferred data to Facebook when users opened the app. Thankfully, their follow-up this year concluded that “period tracking apps were not sharing users’ cycle data as egregiously with third parties” as before. But it still found that some are sharing device information; this is “metadata about your device”, Felsberger explains. When this is used in conjunction with other sets of data, it can help sharpen the picture of you and your habits.
Felsberger was struck by how, while interviewing case studies, she found that “the thought that anybody would be interested in your menstrual data was ludicrous to people, really ridiculous. People were laughing when I asked them this question. They were like, ‘What are they going to do with it?’” She reckons this might be because “we’ve been taught to hide and conceal menstruation for so long”, so the idea that it might be a source of valuable data feels alien.
But in fact, she says, any health-related data can be incredibly valuable to advertisers. Plus, the information that these apps collect isn’t just about cycles. “It’s really holistic: it’s health information, it’s mental health information, it’s consumer choices, it’s lifestyle habits, it’s illness and reproductive choices”, Felsberger says. Details about pregnancy, or whether someone is trying to conceive, can be a goldmine. In fact, this data is thought to be more than 200 times more valuable for targeted advertising than information about age, gender or location, because it marks such a significant change in shopping behaviour.
Yet Felsberger says plenty of her interviewees seemed to believe that the companies behind their tracking apps were entirely altruistic. “There’s this implicit assumption that if somebody does a product for periods, that they care about menstruation, rather than [the potential to make] a lot of money out of it,” she notes. “But menstruation has been a big business for a long time.” The global period care market is estimated to be worth around $69bn (£51bn) by 2035. And it’s thought that femtech (the catch-all term for digital products and technologies dealing with women’s health) will have a global market size of over $60bn by 2027.
While many of us will take a while to feel like we can confide in a new person, says Dr Alice Ashcroft, a researcher in gender equity and tech, “When it comes to things like technology, people are a lot quicker to just trust it – they just download this app and put all of their information on it.” Ashcroft spent years tracking her menstrual cycle digitally, before deleting her app of choice a few months ago. She still thinks the app itself is “great”: she says the company is “really transparent” about the fact that, because users pay for their service, they don’t need to sell data for profit.
So why quit? “My lack of trust is not with the app, which is maybe a controversial thing to say,” she explains. Instead, her concern was sparked by news stories that emerged earlier this year. Back in January, the National Police Chiefs’ Council quietly rolled out guidance on investigating unexpected pregnancy loss. This stated that officers should look at digital devices and health apps to “establish a woman’s knowledge and intention in relation to the pregnancy”.
There’s this implicit assumption that if somebody does a product for periods, that they care about menstruation, rather than the potential to make a lot of money out of it
This made the news in May, and at the time, a spokesperson for the NPCC said that an investigation would only be initiated “where there is credible information to suggest criminal activity”, which “would often be because of concerns raised from medical professionals”. They also said that the police “do not routinely investigate unexpected pregnancy loss”. But, for Ashcroft, “The thought of the police being able to use any data that I had against me is quite a horrific feeling.” This fear is “the key thing” that led her to stop using the tracker.
“The current position is that the police can, and indeed do, seize mobile phones and have been able to access data such as menstruation apps to try to evidence illegal abortions,” says Rachel Fletcher, managing partner and head of crime at Slater Heelis Solicitors. “This would only happen in rare cases where there was intelligence to suggest that a woman had illegally terminated her pregnancy.”
In June, MPs voted to decriminalise abortion in England and Wales, meaning that if this amendment is passed, women will no longer be prosecuted for ending a pregnancy. Medical professionals will still be subject to the 24-week limit and the requirement for two doctors’ approval for the procedure. It was a huge development, marking the most significant change to abortion law in 60 years. The bill still needs approval from the House of Lords and royal assent. But if it is passed, Fletcher explains, “Police would not have lawful grounds to seize data, including a mobile phone, in connection with an abortion, since it would no longer be illegal, and challenges to any seizure should be made.” She adds that “If this occurs, legal advice should be sought without delay to prevent the police accessing data.”
Data privacy and abortion laws are very different in the United States. But developments across the Atlantic, such as the Supreme Court’s rolling back of Roe v Wade in 2022 (a move that prompted many American women to delete their tracking apps, for fear the data could be used against them in states where abortion is now illegal) have also made Ashcroft wary. “I’m aware that politics tend to escalate in the US and then the trends follow over here,” she says. “So I’m kind of seeing that as a warning sign.”
She’s not the only British woman who has been spooked. Jess, 31, tells me that she started “feeling uneasy about what data I was sharing” after Roe v Wade was overturned, and decided to switch apps. The company behind her previous cycle tracker, she says, didn’t make any assurances to alleviate her concerns, so she swapped over to another platform that was more vocal about its data policies.
I’m aware that politics tend to escalate in the US and then the trends follow over here
And Hannah, 32, used a cycle tracker for several years, but a few months back, she remembers seeing “a flurry of news stories coming out about safety and privacy risks for people who use menstrual tracking apps”. This, she says, also coincided with American legislators attempting to further tighten up abortion rules, and with Reform UK leader Nigel Farage claiming that it is “utterly ludicrous that we can allow abortion up to 24 weeks”. “I opened up my app one day during this time and there was a new set of data rules I had to agree with,” she says. “I rejected them, and all my previous period history from the app was gone. Only if I accepted the new data rules could I get it back.”
But the privacy policy, like so many similar documents, felt opaque and difficult to understand. “The data rules were paragraphs upon paragraphs of scary words and I couldn’t process it,” Hannah recalls. Now, she says, she simply writes the date of her period in her phone’s Notes app and counts forward if she’s trying to predict her cycle, “But I’m aware that if I decide to start trying for a baby, I may need to use one of these apps again – I just hope there’s one that is safe.”
What might make digitally tracking your cycle an easier, less intimidating process? Several apps have launched “anonymous mode”, so users can access their platform without providing details such as their name or email address; that’s certainly an encouraging development. Ashcroft reckons there are “two things that need to happen” to improve things: regulation around tracking data needs to be tighter (or, where they exist, regulations need to be better enforced) and “there needs to be a huge emphasis on education” around how our data is used, so that the next generation of users will be able to make more informed decisions.
Meanwhile, Felsberger says she would like to see more research collaborations between cycle tracking companies and research institutes, which would mean that their extensive data sets could help us better understand menstrual health. An NHS-backed app, she adds, could provide an alternative to profit-driven platforms too. “The problem is that we have this huge data gap when it comes to gender and health, and I thought an app that could be designed with clinicians and patients together could help understand where those data gaps are.”
Her work, she adds, is not trying to cause unnecessary alarm: she simply wants us all to ask for “better regulation” and for the apps to “try harder when it comes to protecting data”. Wouldn’t it be nice to be able to better understand our bodies, without having to potentially sacrifice our privacy?
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