This is the Guardian.

Today, millions of us use them, but how private are period tracking apps?

28 days is give or take the average length of a menstrual cycle, but everybody is different and periods are always predictable.

Stress, diet, weight loss, they're all factors among others that can affect how long someone's period lasts or whether it stops altogether.

And while some people get little discomfort, for others, the pain is debilitating. And so around the world, millions of women have downloaded apps to help them track their periods and help them understand their bodies.

Yeah, I guess the weird thing is I can now feel when I'm ovulating because I can check. It shows, you know, I'm like, oh, sometimes I feel that or like my moods or other things.

So just a feeling about your in touch with your body a bit more and you know where you are.

Because I've been on contraceptives now since I was 18 and I'm now 26 and I'd like to know what my mood is like, what my body is like without being on them.

Others find that the apps help them understand how their cycle is affecting their mental health.

It told you a little bit about how you would feel on particular days throughout your period.

And I suffer a bit from anxiety and it helped me to track particularly when I was pre-menstrual ham that might be impacting my anxiety.

There are tens of free-to-use period tracking apps on the market that have undoubtedly helped women to feel empowered in the choices they make about their sex lives and fertility.

What's less clear is what the owners of these apps are doing with the intimate data that people are sharing with them.

Do you remember when you downloaded it, whether you looked at the terms and conditions?

No, I didn't. I definitely didn't. I'm not going to lie.

Is that something you've ever thought about?

No, but to be fair, I just feel like anything on the internet these days are just free-game for everyone.

But I haven't thought about that. But I don't know if it's that... I mean, I guess it is sensitive information, but what can you do?

In the US, the overturning of row versus wade means women in at least 12 states can be prosecuted for seeking an abortion.

And privacy campaigners there are worried that law enforcement officers might use this type of data in court.

So what are these app providers doing to help keep our information safe?

And to what extent is the power in our own hands?

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