Girls usually start going through puberty between the ages of 9 and 16, with the average of 11.
During this time a girl will experience a lot of physical and emotional changes caused by the hormones oestrogen and progesterone.
What happens physically?
Growing
Lots of changes occur over the course of puberty, and happen at different times and rates for everybody. You will notice that you get taller and put on weight, especially around your hips and thighs, and you will start to develop breasts. At around the same time you will find you are getting hairier, and will notice hair beginning to grow on your arms and legs, on your genitals, and in your armpits. Some girls prefer to shave or wax the hair under their arms and on their legs, but it is up to you if you do this or not.
Periods
One of the biggest changes for girls is starting menstruation, which shows your body is developing enough to have a baby. The average age for getting your first period is 12. A period is the time in your menstrual cycle when you bleed from your vagina for a few days, and usually happens once every 28 to 35 days. It is completely normal and natural, and you can use sanitary towels, tampons or menstrual cups to soak up the blood. At first your periods may not be very regular, but they usually settle down. Lots of girls feel a bit uncomfortable when their period comes as it can cause tummy cramps, known as period pain. If you get these you may find a hot water bottle helps!
Vaginal Discharge
As well as periods, the menstrual cycle also causes the vagina to make a clear or milky discharge that might change slightly day to day. This is completely normal and helps to keep the vagina healthy and clean.
Spots
Most teenagers experience getting spots on their face, and unfortunately some people get more than others. These are caused by hormones and have nothing to do with eating chips and chocolate! Some people find using a special face wash helps, but some people get lots of painful spots called acne and may need medication from their doctor.
Sweat
You will also find that you sweat changes, meaning that you sweat more than you did before and that it is smellier, which may cause B.O. (body odour). There are lots of deodorants available which can help, as well as remembering to have regular baths and showers.
What happens mentally?
Sexual feelings
All the extra hormones in your body affect your mind as well, and you may find that you are becoming more interested in sex, start fancying people, and thinking about having a boyfriend or girlfriend. You may also be interested in exploring your own body and what feels good through masturbating (wanking), which is completely normal. All this is part of your developing sexuality.
Emotions
Unfortunately, not all your new feelings will be exciting sexual ones. You might also find you become moodier, and have more arguments with your family and friends, or that you feel more confused and worried about things than you used to because lots of things are changing. It is really normal to feel like this and if you are worried it might help to talk things through with someone you trust.