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The Scientific Process of Puberty

Every person normally goes through puberty but not everyone knows the scientific process behind it. Puberty refers to the biological process whereby a child’s body matures into an adult body that is usually capable of sexual reproduction. But puberty is more to than hair growth, menstruation, voice changes and breast growth.

The Tanner scale is often used to define physical measurements of development based on external primary and secondary sex characteristics.

Using the Tanner scale, we’ll take you through the scientific stages behind puberty for boys and girls.

Tanner Stage 1

Tanner One

The first stage of puberty starts early in childhood and usually occurs after a girl is 9 years old and after a boy turns 10. This early in the process, the child’s physical appearance is usually unchanged, before any physical signs of puberty have become visible.

Towards the end of stage 1, the brain begins to send signals to the body in preparation for adolescence. This is when an area in the brain, called the hypothalamus begins to release the gonadotropin-releasing hormone (GnRH).

The GnRH then moves into a small gland under the brain called the pituitary gland. This gland produces hormones that control other glands throughout the human body. It then releases two more puberty hormones called luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Tanner Stage 2

At stage 2, the physical developments will start to make an appearance. This is where hormones develop more prominently and begin to send signals throughout the body that result in physical changes.

These hormonal changes are different in both girls and boys.


In boys, this hormone travels through the blood to the testes (testicles) and give the signal to start the sperm production as well as the testosterone hormone.

This stage of puberty usually starts in boys around the age of 11. This is when the testicles and scrotum grow bigger in size, and early stages of pubic hair may also form in this area.


For girls, this process begins between 9 and 11 years old. The first physical signs of puberty are the breasts, they start to swell and may cause pain, discomfort, tenderness or tightness as a part of the growing process. The uterus also increases its size, and the growth of pubic hair around the vagina may start.

For girls, this process begins between 9 and 11 years old. The first physical signs of puberty is the breasts, these start to swell and may become itchy or tender as a part of the growing pains. The uterus also begins to grow bigger, and the growth of pubic hair outside of the vagina may start.

Interestingly, it is common for taller and plus-sized girls to experience puberty a little earlier than the latter.

Tanner Stage 3

In stage 3, the appearance of puberty is much more obvious physically.


For boys, this occurs around 13 years old. Some of these changes include:

Wet Dreams

The growth of the testicles will continue into stage 3, and the male child is likely to discover the process of ejaculation and the release of sperm-containing semen.

In addition, boys can experience wet dreams while asleep. Wet dreams are as a result of the increase in the testosterone hormone (a primary male hormone). These are a normal occurrence and cannot be prevented – some adults may also experience this even after full maturity.

Breast Growth

Some boys may even experience breast swelling or tenderness. However, this is temporary and usually disappears within 6 months.

Penis Growth

During this process, the penis begins to fully develop. The male’s penis will get larger, and erections, which a boy begins experiencing as an infant, will become more frequent now.

Growth Spurt

Between 10 to 16 years old boys will experience a growth spurt and subsequently grow taller.

The body will also mold to a different shape. This includes the broadening of his shoulders as well as the onset of weight and muscle gain.

Voice Changes

Before puberty, the male’s larynx is underdeveloped, and the vocal cords are thin (this is why a boys voice is higher pitched than an adult). Puberty causes the larynx to enlarge as well as causing the vocal cords to grow thus deepening the voice.

What’s more, the facial bones begin to grow. Cavities in the sinuses, nose, and the back of the throat grow bigger create more space in the face and gives the voice more room to reverberate.

Other Growth

During this process, hair on other parts of the body start to make an appearance. This includes under the arms, the facial area as well as continued around the penis and scrotum.


Breast Growth

Although breast growth has already started in stage 2, this development will continue in stage 3. At this point, the nipples will also start to protrude.

Hair Growth

Body hair will reach adult levels. Pubic hair will increase in amount and begins to extend laterally, as well as appear darker, coarser and begin to curl. Hair also starts forming under the armpits at this stage.


Although girl’s growth spurt isn’t usually as extensive as boys, they do still grow exponentially during this time period. It is common for girls to grow at least 8 cms per year.


Acne in adolescence is very common. In fact, according to UC Davids Health, acne affects around 85% of teenagers starting at the age of 11 for girls.

Other Growth

At this stage, females start experiencing other bodily changes that set them apart from males at this age. At this point, fat will begin to build up at the hips and thighs. And the hips will already begin to widen in preparation for birth.

Tanner Stage 4

By stage 4, puberty is in full swing and the body has gone through both internal and external changes.

For boys, stage 4 may occur around the age of 14 years. Some of these changes include a continuation of growth and maturation of the testicles, penis and scrotum. What’s more, the scrotum will get darker in colour pigment. Armpit hair and voice deepening becomes permanent and acne may appear.

For girls, stage 4 is mostly a continuation of the previous stages. This means that the breasts take on a fuller shape, pubic hair gets thicker and height growth increases annually.

This stage is also where most get the first period. This typically starts between 12 and 14 years old, but may occur earlier. It can take a while for periods to regulate and usually this will overlap to the next stage.

Tanner Stage 5

Stage 5 is the final stage of puberty and marks the end of the child’s physical maturation.

For boys, the penis, testicles and scrotum will have reached adult size, pubic hair will have spread to the inner thigh and facial hair may grow faster and become thicker. At the age of 15 (where most boys experience this stage) the growth spurt may begin to slow down, but muscle growth may still be on the rise. By 18 years old, most boys may have reached full growth.

With the exception of the breasts, girls may reach full adult size and shape at 15 years of age, while breast growth may continue until 18 years of age. Menstruation periods should become regular after six months to two years. Other changes include pubic hair growth that may reach the inner thighs, full development of the genitals, hips and thigh growth.

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