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.