Most girls start their periods when they're about 12, but they can start as early as 8, so it's important to talk to girls from an early age to make sure they're prepared before the big day.
Many parents feel awkward talking about periods, especially with pre-teen girls, who can seem to get easily embarrassed.
One way round this is to respond to questions or opportunities as they arise. David Kesterton, who organises the FPA's Speakeasy courses – which teach parents how to talk to their children about puberty, sex and relationships – says clear speaking and down-to-earth, age-appropriate language is key.
"Parents often ask me when the right age to talk to girls about starting periods is, and I recommend that it should be an ongoing process rather than a formal sit-down talk.
"You can use TV ads for tampons, or buying sanitary towels at the supermarket, for example, to start the conversation with girls about periods. Or simply ask your daughter what she already knows and go from there.
"Whenever possible, use clear language, like 'vagina', even though you may feel uncomfortable using these words. Emphasise that periods are completely normal and natural – they're part of growing up and all women have them.
"And don't forget boys. They, too, need to learn about periods. Talk to them in the same way as girls about the practicalities, mood changes that can come with periods, and the biological reason behind periods, and it will keep them informed, as well as help them to understand what girls go through each month."
Here are some of the questions that you, as a parent, might get asked by girls about periods, with suggestions on how to answer them:
Signs that your period is on its way are if you've grown underarm and pubic hair. Typically, you'll start your periods about 2 years after your breasts start growing and about a year after getting a white vaginal discharge. The average girl will get her first period around 12 years old, but it varies from person to person.
Your periods will start when your body is ready. That's usually between the ages of 10 and 16.
See a GP if your periods haven't started by age 16 (or 14 if there are no other signs of puberty either).
Possible reasons include being underweight, doing lots of exercise (including dance, gymnastics and athletics) and a hormone imbalance.
Read more about Why haven't I started my periods?
Talk to your mum or another adult you trust about what you can expect before it actually happens.
It's a good idea to start carrying sanitary pads or tampons around with you in advance, so you aren't scrambling to find some when your period finally arrives.
If you find yourself at school without a pad or tampon, talk to a female teacher or the school nurse. They're used to being asked and they'll want to help you out.
When your first period arrives it might not last very long, as it can take your body some months to get into a regular pattern. As a general rule, once they're settled, you'll have a period every 28 to 30 days and it will last 3 to 7 days.
It might seem a lot, but it's only about 3 to 5 tablespoons. It's not a sudden gush – you'll just see a reddish-brown stain on your pants or on your sheets when you wake up in the morning.
Part of becoming a woman is dealing with embarrassing mishaps. There are ways of covering up stains until you're able to change your clothes, such as tying a sweatshirt around your waist. Keep a spare pair of pants and tights at school or in your bag, and avoid wearing light-coloured trousers and skirts during a period, just in case.
This is really up to you. Both tampons, menstrual cups and towels (or pads) are safe and suitable for girls who have just started their periods. You'll probably want to use pads for your very first period, though, as tampons and menstrual cups can take a bit more getting used to. It might be worth experimenting until you find the product that suits you best.
No, it can't. When you insert a tampon, it stays in your vagina. All tampons come with a string at one end that stays outside your body. You can remove the tampon at any time using this string.
Read the full answer to Can a tampon get lost inside me?
If you forget to remove your tampon, it can turn sideways or become compressed at the top of your vagina. This can make it difficult or impossible for you to pull it out. If you think you've left a tampon in and you can't get it out, go to your GP. They can remove it for you.
Read the full answer to What if I forget to remove my tampon?
Read more articles on the menstrual cycle.