Puberty: a small guide to what you need to know

Boys growing up

In four years, the average teenage boy will grow a foot taller, put on a stone of muscle, drop an octave in the pitch of his voice and develop 40% more heart muscle.
Puberty for boys
The beginning of puberty for boys usually begins between the ages of 10 and 16 and ends between 14 and 18. The main body changes are:
- your scrotum (balls) and penis grow. You may wake up one morning to find you have had a wet dream (sexy dream). They are called "wet dreams" because semen is released from your penis leaving a patch on your sheet slightly wet. This is perfectly normal;
- pubic hair begins to grow under your arms, on your testicles, above your penis;
- you grow in height and weight, often in spurts. You may find your clothes don't fit you as - - - you grow quickly;
- your voice breaks and becomes deeper;
- you sweat more and may get spots;
- you will be stronger than you used to be;
-later your face will also get more hairy and you will have to think about shaving.

Grown-up girls

Puberty for girls
The beginning of puberty for girls takes place between the ages of about 9 and 15. The main body changes:
- you grow in weight and height, often quite rapidly. Your face may become fuller and your hips wider and fuller. Putting on weight in this way does not mean that you are fat and you should be careful about dieting while your body is still growing;
- your breasts begin to appear and your nipples grow larger. Some girls' nipples stick out a lot, some look flat and some are inverted. All these are normal. Some girls feel a tingling or have tender breasts. Sometimes one breast grows more quickly than the other (the other one will catch up eventually). All these things are normal too. Your breasts will continue to grow in fullness and roundness;
- you become more hairy;
pubic hair grows around your genitals and under your armpits. Some fine hair can grow on your upper lip; you may get hairier legs;
- you will be stronger than you used to be and your voice may be slightly lower;
- your skin and hair get greasier than they use to and later you will sweat more;
- you may tend to get spots;
- you sometimes get a white discharge on your pants from your vagina. This is quite normal and is a sign that your period will start in the coming year;
- later you will have regular periods;
- the lips of your vulva (the external female sex organs between your legs) grow and become more full.

Growing taller is one of the first external signs that a girl is experiencing puberty. This is just the beginning
Kicked off by sex hormones, the growth spurt is closely related to the arrival of periods. Once the ovaries are mature, the legs have generally finished growing. Any increase in height after periods have begun, usually comes just from the torso. A general rule is that a girl will grow no more than 6cm after her first period.
By 14, on average, the spine has also finished growing. Lastly, the bones of the pelvis widen and become smooth, in preparation for childbirth. This can occur up to the age of 18 or even later.

On the blob

When a girls starts her periods it's often hailed as the first step towards becoming a woman. Monthly bleeding from the vagina first begins during teenage years and continues until a woman is in her forties or fifties.
Periods are caused by changing hormone levels that fluctuate in a regular cycle that controls fertility. This cycle is known as the 'menstrual cycle'. The average length of the menstrual cycle is 28 days, but ranges anywhere between 19 and 37 days.
The menstrual cycle
Day one of the menstrual cycle is marked by the beginning of a period, also known as 'menstruation'. During menstruation, the thick uterus (womb) lining, which built up during the previous menstrual cycle, is released along with blood and mucus. The uterus contracts to force out the old lining.
This can also cause stomach cramps in some women. On average only 40ml of blood are lost during a period, but the amount can be five times more or five times less. Periods last around 5 days.
Half way through the menstrual cycle, a mature egg is released from one of the ovaries. If this egg is fertilised, pregnancy will follow. Fertilisation will only occur if there has been unprotected sex. In most cases, the egg is not fertilised and the menstrual cycle will begin again.
After menstruation, rising levels of sex hormones trigger an egg to mature in one of the ovaries. Meanwhile, the lining of the uterus prepares to receive an embryo. It becomes at least five times thicker and is filled with blood and mucus.
False starts
In many girls, the start of bleeding does not mean that sexual maturity has been reached. Often there will be no egg released for the first month. On the other hand, some girls will release eggs for several months before bleeding occurs.
PMS
Pre-Menstrual Syndrome, or PMS, is the name for some of the symptoms girls experience in the days leading up to a period. These include breast pain and water retention. A girl might also become irritable and tired, or suffer from nausea and headaches.
More pleasant perhaps is a craving for chocolate and stodgy food. As many as three quarters of women experience some form of PMS and it can be worse during teenage years as the menstrual cycle is becoming established

Changing shape

Before puberty, boys and girls have a very similar physique. But they both change shape noticeably as increasing amounts of sex hormones sculpt their bodies in different ways. Boys experience a large degree of muscle development after the skeleton has finished its growth.
In girls, this stage is much less pronounced. Instead, the female sex hormone oestrogen triggers the laying down of fat. This is concentrated at the hips and bust and is perfectly normal. It is less noticeable in girls who exercise a lot.

Breaking voices

Surprisingly, both girls and boys are affected by voice changes during their teenage years.
In girls, the change is hardly noticeable - their voices only go down by a couple of tones. Boys however experience quite a dramatic change in tone. Their voices might drop by as much as a whole octave.
The voice usually begins to deepen shortly after the penis has finished its phase of rapid growth. It is not clear why this change occurs. The males of other species develop deep voices to attract women and to intimidate other men. It is possible the human male voice developed for the same reasons.
Croaking and warbling
Changes to the voice take place gradually over a period of time. In some boys however, there can be a dramatic period of change. This is described as their voice 'breaking'. Boys at this time can struggle to control their voice and often start to warble or croak. This can be embarrassing, but usually doesn't last very long.

Hair, hair, everywhere!

Not only do you gain your first pubes, but your whole body becomes more hairy when you're a teenager.
Firstly, hair on the arms and legs becomes more noticeable. Next, pubic hair starts to grow around the groin and under the arms. Finally, boys grow hair on the chest and sometimes the back and they start to grow a beard. Teenagers want to grow this hair at the same time as everybody else. It can be difficult to be the one who has the earliest hairy armpits, or the latest.
Pubic hair
Pubic hair is quite different from hair on the head. Instead of forming a round shape, the hair is oval. It is always short and has a coarse and curly texture. The growth period for pubic hair is short. Within six months, the hair follicle dies and the hair falls out. Pubic hair never gets a chance to grow longer.

Sweating it out

Teenagers are renowned for their smelly bedrooms. This is not just because they cannot be bothered to wash. Teenagers do start to sweat in a slightly different way.
Humans have two types of sweat glands. 'Eccrine glands' are found all over the body and produce a slightly acidic watery fluid. When this sweat evaporates from the skin it cools the body down. Humans rely on this sweat to control body temperature. It has no odour of its own, but does start to smell when bacteria on the skin's surface begin to digest it.
Smelly sweat
An altogether stinkier kind of sweat is produced by the 'apocrine glands'. These glands only start working at puberty. They secrete a thick, waxy, greyish substance which is diluted by fluid from other glands nearby. Although it has no odour itself, when bacteria start decomposing it, it releases a strong distinct smell - BO.
Apocrine glands are only found in the armpits, belly button area, ears, groin and nipples. The sweat they produce has no role in temperature regulation. It is released in response to stress, emotion and sexual excitement…