Puberty describes the time in life when the body matures sexually and the reproductive organs become functional.

It's caused by a release of the sex hormones testosterone and oestrodiol in the body.

Testosterone is the male sex hormone that's produced by the testis (the male sex organs). Oestrodiol is the main female sex hormone that's produced by the ovaries.

Puberty causes a number of changes to occur which can be categorised as:

  • physical changes – including rapid growth spurts, the development of breasts in girls and an increase in penis size in boys
  • psychological changes – which can cause teenagers to become moody, self-conscious and aggressive
  • behavioural changes  which can cause some teenagers to experiment with new and potentially risky activities, such as smoking, drinking, alcohol and sex

Read more about the symptoms of puberty and the causes of puberty.

When does puberty start?

There's no set age when puberty starts. The age at which puberty begins and the rate of development differs between individuals.

Most girls begin puberty at 8-14 years of age, with 11 the average age. Girls develop quicker than boys. Most girls reach full sexual maturity within four years of starting puberty.

Boys tend to develop later than girls. Most boys begin puberty at 9-14 years of age, with 12 the average age. Most boys reach maturity within four years of starting puberty.

Early or delayed puberty

If a child experiences puberty earlier than normal it's known as early or precocious puberty. Delayed puberty is where puberty occurs later than normal.

In some cases, early or delayed puberty may be caused by an underlying condition. If there's no obvious cause, such as a long-term illness, tests may be needed to help diagnose any problems.

Read more about the complications of puberty.

Help and support during puberty

Puberty can be a difficult time because your body is developing at a time when you may feel self-conscious about your body image.

This period can be an 'emotional rollercoaster' and you may experience a range of emotions including unexplained mood swings, low self-esteem, aggression and depression.

You may find it helpful to talk to someone close to you, such as a friend or relative. You could also speak to your GP, or you could contact a support organisation such as ChildLine (0800 1111). If you prefer you could contact them through the ChildLine website.

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The physical changes that occur during puberty are usually marked by distinct stages of development.

The stages are known as Tanner stages, named after Professor James Tanner, the child development expert who first identified them.

The Tanner stages give average ages of development, although there can be significant variation among children and teenagers. You therefore shouldn't worry if you reach a stage of puberty before or after your friends do.

Tanner stage one

Tanner stage one describes the body before the onset of puberty. This period is sometimes referred to as pre-pubertal.

Tanner stage one isn't associated with any particular ages, and there aren't any significant physical changes in girls or boys.

Tanner stage two

In girls:

  • usually occurs at around 11 years of age
  • breast buds develop – they're often very tender during the early growth stages (this is normal); one breast bud may also start to develop many months before the other one – again this is normal and the breast tissue will even up over the course of puberty
  • your areola (area of skin surrounding the nipple) will begin to swell
  • pubic hair will start to develop along the labia (lips of the entrance to the vagina)
  • the womb becomes larger in response to oestrogen
  • you'll grow taller by 7-8cm (2.8-3.2 inches) a year

In boys:

  • usually begins at about 12 years of age
  • your scrotum (the pouch containing the testes) will begin to thin and redden; your testicles will increase in size
  • fine pubic hair will start to appear at the base of your penis

Tanner stage three

In girls:

  • usually occurs after the age of 12
  • the tissue beneath the areola continues to grow and spread out to provide the fullness of your breast; you may need to buy your first bra
  • your pubic hair will become coarser and curlier and you'll begin to grow underarm hair
  • you may develop spots (acne, see below) on your face and back
  • you'll grow taller by an average of 8cm (3.2 inches) a year – the highest growth rate

In boys:

  • usually occurs after the age of 13
  • your penis will grow and lengthen, and your testicles will continue to grow
  • your pubic hair will become thicker and curlier, spreading to the soft mound of skin above your genitals
  • your breasts could swell slightly due to the growth of breast tissue; about a third of teenage boys have some breast tissue growth which usually settles down after a few years
  • you may begin to have 'wet dreams' – involuntary ejaculations of semen during sleep
  • your voice should 'break' (the pitch and tone of your voice may start to suddenly change for short periods of time)
  • the size of your muscles will increase, and you will grow taller by 7-8cm (2.8-3.2 inches) a year

Tanner stage four

In girls:

  • usually occurs at the age of 13
  • your breasts slowly develop into a more adult shape, with your nipple and areola swelling to produce a secondary mound above the level of the breast (this will disappear after the rest of your breast has developed)
  • your pubic hair will start to look more adult-like in appearance but won't have spread to your inner thighs
  • you'll usually have your first period and you should start having regular periods in 6-12 months of your first one (around 10% of girls start their periods during stage five)
  • your growth rate will begin to slow down, growing taller by an average of 7cm (2.8 inches) a year

In boys:

  • usually occurs at around 14 years of age
  • your penis and testicles will continue to grow, and your scrotum will become darker
  • your pubic hair will appear more adult-like, but won't have spread to your inner thighs
  • you should start growing underarm hair
  • your voice will change permanently
  • you may develop acne

Tanner stage five (final stage)

In girls:

  • usually occurs at just over 14 years of age
  • your breast becomes adult-like in shape
  • your pubic hair should spread to your inner thigh
  • your genitals should have fully developed by the end of this stage
  • you'll have stopped growing and reached your adult height 1-2 years after your periods started; from the age your periods start, you'll have another 5-7.5cm (2-3 inches) of growth in height

In boys:

  • usually starts at about 15 years of age
  • your genitals will look like an adult’s, and pubic hair will spread to your inner thigh
  • you'll begin to grow facial hair and may have to start shaving
  • your growth should slow down and you should stop growing at around 16 years of age (but your muscles may continue to grow)
  • most boys will have reached full adult maturity by 18 years of age


During puberty, your body becomes more sensitive to the hormone testosterone, which is present in both boys and girls. Testosterone causes small glands in your skin to produce too much oil (sebum).

Dead skin can also block the opening of hair follicles (the small tubes in your skin that hold a hair in place). The sebum can build up behind the blocked follicle, which can cause spots (blackheads or whiteheads) to develop.

Hormonal changes also alter the levels of acid in your skin, encouraging the growth of bacteria. If bacteria infect a blocked hair follicle, a deeper infection can occur, such as a spot (pustule) or nodule.

Mild to moderate acne can usually be treated with antibacterial cream. In more severe cases, your GP may recommend antibiotic tablets.

Read more about acne.

Body odour

During puberty, your body develops large sweat glands around your armpits, breasts and genitals. These are known as apocrine glands.

Apocrine glands release sweat in response to stress, emotion and sexual excitement. In some cases, the excess sweat can cause body odour.


A girl's monthly periods usually start between 11-14 years of age (usually at 12-13). They continue until the menopause, which usually occurs around the age of 50.

In the days leading up to your period, you may have a number of symptoms, including:

  • sore breasts
  • irritability
  • backache
  • spots
  • feeling very emotional or upset

These symptoms should pass once your period starts. Many girls and women have pain or cramping in their abdomen (tummy), back and vagina. This is often referred to as period pain. Taking paracetamol may help to relieve period pain.

Psychological and behavioural changes

Puberty can often be a particularly difficult time. You're forced to cope with changes in your body and possible side effects, such as acne or body odour, just at the time when you feel self-conscious about your body and self-image.

Puberty can also be an exciting time, as you develop new emotions and feelings. However, the 'emotional rollercoaster' experienced during puberty can have psychological and emotional effects such as:

  • unexplained mood swings
  • low self-esteem
  • aggression
  • depression

These feelings can be a normal part of growing up and going through puberty. But if they're having a serious impact on your life, you may wish to talk to someone close to you, such as a friend or relative.

You could also ask your GP, or you could contact a support organisation, such as ChildLine, for free and confidential help and advice. Their helpline number is 0800 1111, or you could contact them through the ChildLine website.

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Who can get it

Puberty is started by certain genes and hormones in the body.

It's not yet fully understood why some people experience puberty earlier or later than others, although there are a number of possible factors.


Research has found that two genes present at birth, known as GPR54 and KiSS1, are responsible for the onset of puberty.

The GPR54 lies dormant (inactive) for many years until it's suddenly activated by special chemicals called kisspeptins that are produced by the KiSS1 gene.

The process of puberty starts when kisspeptins turn on the GPR54 gene, sending signals to your brain and triggering a chain reaction in your body.

An area of the brain known as the hypothalamus activates a hormone called gonadotropin-releasing hormone (GnRH). GnRH sends a signal to the pituitary gland (a pea-sized gland near the base of the brain) to release hormones that stimulate the ovaries (in girls) or testicles (in boys) to make sex hormones.

This chain reaction and release of hormones brings on the changes of puberty.


The ovaries and testicles produce two sex hormones  responsible for changes that occur during puberty.

In boys, testosterone is produced by the testes (male sex organs). Testosterone stimulates the development of the penis and testes and causes muscle and pubic hair growth. It's also responsible for lowering the voice.

Women and girls also have testosterone in their body, which is produced in small amounts by the ovaries to help maintain muscle and bone strength.

Oestrodiol is the main sex hormone in girls. It's produced by the ovaries and stimulates growth of the breasts and reproductive system, and helps regulate the monthly menstrual cycle (periods).

Boys and men also have oestrodiol in their body. It's produced in small amounts by the brain and testes to help maintain bone density.

Triggers of puberty

It's thought puberty may be triggered by environmental and genetic factors.

Studies have shown that on average, black girls start puberty earlier than white girls. But there's no evidence to show black boys mature faster than white boys.

Diet and nutrition are also thought to be important factors, particularly in girls. Studies have shown that girls who are overweight or obese tend to start puberty earlier, while girls with a lower body weight tend to start later.

The rising trend of obesity in girls could explain why the average age of girls beginning puberty has been falling over recent years. But it's not known why obesity doesn't have the same effect in boys.

There's a lot of uncertainty regarding why certain factors seem to trigger puberty and research in this area is ongoing.

Read more about early or delayed puberty below.

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Puberty is when a child's body begins to develop and change as they become an adult.

Signs of puberty include girls developing breasts and starting periods, and boys developing a larger penis and testicles, a deeper voice and a more muscular appearance.

The average age for girls to start puberty is 11, while for boys the average age is 12. However, it's perfectly normal for puberty to begin at any point between the ages of 8 and 13 in girls and 9 and 14 in boys.

There's not usually any need to worry if puberty doesn't start around the average age, but it's a good idea to speak to your GP for advice if it starts before 8 or hasn't started by around 14.

In some cases, early puberty or delayed puberty could be a sign of an underlying condition that may need to be treated.

Early puberty

Early puberty, also called precocious puberty, is when:

  • girls have signs of puberty before 8 years of age
  • boys have signs of puberty before 9 years of age

Some girls and boys may develop certain signs of puberty at a young age, but not others. For example, girls may start periods before the age of eight but have no breast development. See your GP if this happens to your child.

Causes of early puberty

It's not always clear what causes early puberty. It may just be a tendency that runs in your family.

Occasionally it can be caused by:

  • a problem in the brain, such as a tumour
  • damage to the brain as a result of an infection, surgery or radiotherapy
  • a problem with the ovaries or thyroid gland
  • a genetic disorder, such as McCune-Albright syndrome

Early puberty mostly affects girls and often has no obvious cause. It's less common in boys and may be more likely to be associated with an underlying problem.

Tests and treatments for early puberty

Your GP may refer you to a specialist if they think there could be an underlying cause that needs to be investigated.

Tests that may be carried out include a blood test to check hormone levels, a hand X-ray to help determine likely adult height, and an ultrasound scan or magnetic resonance imaging (MRI) scan to check for problems such as tumours.

Early puberty can be treated by:

  • treating any underlying cause
  • using medication to reduce hormone levels and pause sexual development for a few years

Treatment with medication is usually only recommended if it's thought early puberty will cause emotional or physical problems, such as a very short stature or early periods in girls, which may cause significant distress.

Delayed puberty

Delayed puberty is when:

  • boys have no signs of testicular development by 14 years of age
  • girls have not started to develop breasts by 13 years of age, or they have developed breasts but their periods haven't started by 15

Causes of delayed puberty

It's not always clear what causes delayed puberty. It may just be a tendency that runs in your family, and is generally more common in boys.

Occasionally it can be caused by:

Tests and treatments for delayed puberty

Your GP may refer you to a specialist if they think there could be an underlying cause that needs to be investigated.

Tests that may be carried out include a blood test to check hormone levels, a hand X-ray to help determine likely adult height, and an ultrasound scan or MRI scan to check for problems with glands or organs.

Delayed puberty can be treated by:

  • treating any underlying cause
  • using medication for a few months to increase hormone levels and trigger the start of puberty 

Treatment with medication is usually recommended if the lack of development is causing problems, such as significant distress.

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The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website nhs.uk
Last Updated: 12/05/2016 13:56:22