Meet Body OS by Rerein

A whole new way to understand yourself

We've taken the science behind your body, brain, hormones and menstrual cycle and turned it into a whole little world you can actually explore. Real science, translated into language that makes sense, with interactive little discoveries that help everything click.

Explore Body OS ↓  Download on the App Store

Imagine you're a phone 📱✨

You know how your phone has apps, settings and notifications? Your body has its own version of all of that. It's not literally a phone, obviously, but it's a surprisingly good way to picture what's happening inside you.

✨ Hormones are the notifications
🦴 Body parts are the apps
✈️ Cycle phases are phone modes

You can open Hormone HQ and see how hormones communicate with different parts of your body. You can explore your menstrual cycle and understand what's happening at different stages. You can look up a complicated medical word and have it translated into something you actually understand.

And that's the whole idea behind Body OS. Instead of giving you another complicated diagram and hoping it sticks, it lets you tap around and discover things for yourself.

Explore Body OS

👆 Tap to explore

We've taken the things you're already familiar with, like apps, notifications and settings, and used them to explain how your body actually works.

Girls GlossaryMedical words, translated into actual human language.

Inside Girls Glossary

It's the science, but in your language.

You know when someone says a medical word and you sort of understand it... until you try to explain it to somebody else? That's why there's a Girls Glossary. You get what the word means, the actual science and then a girl-talk translation that makes the whole thing click.

So if you're wondering about cramps, discharge or why period blood can look brown, you don't have to go down a search-engine rabbit hole just to understand one thing.

TRY THIS ONE 👆

Tap Cramps on the phone.
Read the 🔍 science bit first.
Then open 👄 Girl talk translation. That's the difference.

IN THE APP: There's a whole glossary to dip into whenever a word pops up that you want explained.

Hormone HQWhat are your hormones telling your body? Open a notification.

Inside Hormone HQ

Your body's got notifications too. 🔔

Remember the phone comparison? Here's where it gets really good. Hormones are messages. They're released in one place, travel through your body and tell certain cells or organs that it's time to do something.

So Hormone HQ shows them as notifications. You can actually open one and see who sent it, where it's going and what it's doing. Suddenly, hormones aren't just mysterious things people blame everything on.

GO ON, OPEN ONE 👆

Tap the Ghrelin notification (that's involved in hunger).
See where it comes from and what it's telling your body.
Open the 👄 girl-talk translation for the everyday explanation.

IN THE APP: There are more hormone notifications to explore, each with the science and its translation.

Cycle modesFour phases, explained like the settings on your phone.

Inside Let's Talk

Same phone. Different settings. 📱

You know how your phone isn't on the same setting all day? Well, your body isn't doing exactly the same thing all month either. Across your menstrual cycle, hormone levels change, and some people notice differences in their energy, mood or symptoms.

So the four phases have phone-mode nicknames. Period is Low Battery. Follicular is Notifications On. Ovulation is Full Brightness. Luteal is Airplane Mode. They're ways to remember the phases, not instructions for how you're supposed to feel.

HAVE A LOOK 👆

Choose 🪫 Period (Low Battery).
See what's physically happening during that part of your cycle.

IN THE APP: You can explore all four phases, read the other Let's Talk topics and use the Cycle Calendar to spot patterns that are personal to you.

Quick SOSNot sure what to ask? Start with the question in your head.

Inside Quick SOS

You can just ask the question.

Sometimes you don't know the proper word for what you're trying to find out. You've just got a question. Maybe it's a bit embarrassing, maybe you're worried, or maybe you can't quite explain what you mean.

That's what Quick SOS is for. You can ask it in your own words and it'll help you find explanations that are already in Body OS. You don't have to know the medical term before you're allowed to learn about it.

And an important detail: it's not an AI inventing medical advice. It searches the app's existing content. It's there to help you find information, not to diagnose you.

TRY A QUESTION 👆

Tap the example question on the phone.
Open the Thought Translator result it finds.

Thought TranslatorFor those “why do I feel like this?” moments.

Inside Thought Translator

For the “why am I like this today?” moments.

Ever had a day where you suddenly feel tearful, exhausted or uncomfortable in your own skin, and you can't even explain why? Thought Translator starts with the thought you'd actually have, rather than expecting you to know the science first.

You open something familiar, explore a few possible reasons you might be feeling that way and see what might help. Not every feeling has one neat explanation, and it doesn't pretend otherwise.

SEE WHAT I MEAN 👆

Open the 😭 crying thought.
Have a look at the ❤️ When to ask for help section as well.

IN THE APP: There are six thoughts to explore, from cramps and spots to those days when every outfit suddenly feels wrong.

Secretly SearchThe body questions you might not fancy asking out loud.

Inside Secretly Search

And then there are those questions. 👀

The ones you really want answered but might not fancy asking out loud. Like, can you swim on your period? Can somebody else tell you're on it?

Secretly Search gives those questions their own space, with straight answers and no making you feel awkward for being curious. Because they're perfectly reasonable things to want to know.

PICK ONE 👆

Open Can I swim on my period? and have a read.

IN THE APP: You'll find more of the questions people tend to keep to themselves, explained properly.

The important small print 💗

Subscription terms and cancellation

A Body OS subscription gives the named member access to Rerein content and interactive tools while the subscription is active. Subscriptions are billed in advance and renew automatically monthly or annually until cancelled.

Subscribed through the App Store? Apple handles the billing. Manage or cancel from Settings → your name → Subscriptions on the device, at least 24 hours before the renewal date.

Subscribed on the web? Cancel at any time from your MemberSpace account. Access continues until the end of the period already paid for.

Body OS is for household use only and must not be shared, resold or republished. Rerein has stated that your subscription price will remain the price you joined at for as long as the same subscription remains active.

Private data and account information

Her private Body OS entries stay locally on her device. Because Rerein does not hold that information, it cannot be recovered if browser data is cleared, the app is deleted or the device is changed. The grown-up account information required to manage access, support and billing is handled separately. Read the full Privacy Policy.

Parental consent and under 16s

If the member is under 16, a parent or legal guardian must create and hold the account, control billing and manage the subscription. If she turns 16 while subscribed and wants her own account, contact Rerein for help moving it across.

Is Body OS medical advice?

No. Body OS is educational content. It does not diagnose, treat or replace support from a GP or qualified health professional. If you are worried about her physical or mental health, please speak to an appropriate health professional.

What if she is not interested yet?

That is completely fine. Body OS is made to be dipped into. One app, one question and one sudden “ohhh, that makes sense” moment at a time. It can sit quietly until she needs it.

Who is Body OS for?

Maybe you've got a hundred questions about your body. Maybe you're only just finding out the things you wish someone had explained years ago. Or maybe you're here because someone you love is growing up, and you want to help them make sense of it all.

The girl figuring it all out

You're 8, 12 or 16. Your body's changing, you've got questions about periods, hormones, your brain or growing up, and you'd quite like an answer that actually makes sense. Start exploring. You don't have to know what to ask yet.

The woman still connecting the dots

You might have had periods for years and still wonder why certain things happen. No one gave you a proper explanation the first time around? You're welcome here too. Curiosity doesn't have an age limit.

The person who wants to help her

Mum, dad, carer, grandparent, auntie, uncle or someone she trusts. Perhaps you want to help answer a tricky question, or explore something together. You don't need to have all the answers to get the conversation started.

 Explore Body OS on the App Store

Body OS is here for learning, not medical diagnosis. If something is painful, worrying or doesn’t feel right, speak with a trusted adult, school nurse, pharmacist or GP. These interactive phones are simplified previews, not the full app.