Puberty is what happens in children's bodies that changes them into adults. After puberty, people are able to make children. A girl who has gone through puberty can become pregnant and have a baby. At puberty, a boy's body begins making sperm, and he starts to be able to ejaculate, which is semen coming out from his penis when he is sexually excited. If he has sexual intercourse (sex) with a girl, he can make her pregnant.

Puberty is started by hormones, which are chemicals that tell parts of the body to do things. Today, on average, girls start puberty at age 10 or 11, and boys at age 11 or 12. However, people all over the world start puberty at different ages. Changes that happen to boys and girls during puberty include the sex organs growing bigger, hair appearing on the body, and growing taller and stronger. These changes are called secondary sex characteristics. People often notice boys' voices getting deeper, and girls growing breasts and starting to menstruate (have periods).

Because puberty is the time in a child's life when he or she becomes able to make children, this is seen as very important. Therefore, people in many countries around the world have different ways of marking this event.

How the body controls puberty 

Puberty is started and carried on by different hormones. Hormones are chemicals that tell parts of the body to do things. Hormones are made by glands in the body. Glands are organs (special parts) of the body that make hormones.

This is what happens during puberty:

A gland at the bottom of the brain called the hypothalamus sends gonadotropin-releasing hormone (GnRH) into a nearby gland called the pituitary gland.
GnRH causes cells in the pituitary gland to make two hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH). LH and FSH are types of hormones called gonadotropins. The bloodstream carries these hormones around the body.
LH and FSH make the gonads grow larger and start producing their own hormones, estradiol and testosterone. A girl's gonads are her ovaries, and a boy's gonads are his testicles (also called testes). Both ovaries and testicles produce estradiol and testosterone, but ovaries produce more estradiol and testicles produce more testosterone. Estradiol and testosterone are types of hormones called steroid hormones. Steroid hormones are also made by the body's two adrenal glands, which sit on top of the two kidneys.
When the amount of estradiol and testosterone in the body increases, various parts of the body change.

When puberty starts and ends 
On average, girls begin puberty at ages 10–11; boys at ages 11–12. Girls usually complete puberty by ages 15–17, while boys usually complete puberty by ages 16–17. The major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average between ages 12–13; for males, it is the first ejaculation, which occurs on average at age 13.

In rich countries in the 21st century, the average age at which children, especially girls, reach puberty is lower compared to the 19th century, when it was 15 for girls and 16 for boys. This can be due to  improved nutrition resulting in rapid body growth, increased weight and fat deposition, or eating meat from animals which have been dosed up with oestrogen.

This is the general picture, but people round the world may start puberty at different ages. This is because their environment (things around them) may differ quite a bit. Here are some of the things that make puberty happen at different ages in people:

Genetics. Genetics is the study of how parents pass on to their children some of the way they are through their genes. Half of a person's genes come from the mother. The other half come from the father. Some studies have found that mothers and daughters tend to start puberty at about the same age.
Diet. Boys and girls who have a good diet – who eat healthy food – tend to start puberty earlier. Today, people start puberty younger than in the 1840s. For example, in Norway, girls born in 1840 had their first period (see below) at an average age of 17 years; in France the average age was 15.3 years; and in England it was 16.5 years. This may be because people have better food to eat today.
Exercise. Young people who exercise a lot, such as athletes and gymnasts, may start puberty later. It may also happen more slowly for them. This is thought to be because their bodies use up the food that they eat faster. This causes them to have less body fat, so there is less leptin to tell their brains to start puberty.
Obesity. Obesity is the state of being very overweight. A scientific study seems to say that girls who are obese start puberty early. Some obese girls have started growing breasts before the age of nine years and have had their first period before 12 years. This could be because a woman who is pregnant needs more nutrients (chemicals the body needs to stay alive) to support her baby. Therefore, if a girl is obese, her body fat sends signals to her brain that she is ready to become pregnant. Girls who have early puberty can have health problems later on in life.
Illness. Boys and girls who are sick for a long time, especially with illnesses that cause them to have a poor diet, tend to start puberty late. For example, this often happens to people who suffer from anorexia nervosa. Anorexia nervosa, often called "anorexia" for short, is an eating disorder. People with anorexia think that they are fat, or are very afraid of becoming fat. They try to lose weight by eating too little and doing too much exercise. To avoid gaining weight, they do not eat the amount of food their body needs. This causes them to stay at a weight that is not normal for their age and height.
Stress. It is thought that people who are under a lot of stress start puberty later. Some research seems to show that girls have their first period a bit later when their fathers are not around when they are young, when they have a stepfather, if they have been sexually abused for a long time, or if they were adopted by their parents from another country at a young age. On the other hand, the first period may happen a bit later when a girl grows up in a large family with her natural father around. However, scientists are not sure how correct these studies are. Not many studies have been done to find out if stress also causes boys to start puberty later.
Chemicals. Some scientists think people may start puberty earlier because their bodies are affected by chemicals such as estrogens and progestagens that are put in the environment by humans. Another chemical that may cause early puberty is Bisphenol A (BPA). It is used to make plastics, such as some types of baby bottles, water bottles and sports equipment.

Girls usually reach their adult height and become sexually mature (able to have babies) about four years after puberty starts. Boys keep growing for about six years after puberty starts. Puberty in boys starts off more slowly than in girls, but then speeds up later on. Although boys are usually about  shorter than girls before puberty begins, men on average end up about  taller than women.

Body changes in males
For most boys, puberty takes about six years and ends when they are about 17 or 18 years old. At the end of puberty, a teenager is usually about 10 to 30 centimetres (cm) (4 to 12 inches (in)) taller, 7 to 29 kilograms (kg) (15 to 65 pounds (lb)) heavier, and stronger. He is also able to make a woman pregnant (have a baby).

Sex organs grow bigger

The first sign of puberty in boys is that their testicles (also called the testes) and scrotum (the "bag" that the testicles are in) grow bigger. Before puberty, each testicle is about 1.5 to 2 cm (0.6 to 0.8 in) long and has a volume of about 2 to 3 cubic centimetres (cc) (0.1 to 0.2 cubic inches (cu in)). About six years after puberty starts, the testicles reach their adult size. The volume of an average adult man's testicle is about 18 to 20 cc (1.1 to 1.2 cu in). However, it is normal for some men to have testicles smaller than this size, and for other men to have larger testicles.

The penis also grows bigger during puberty. At the start of puberty, the average length of the penis is 6 cm (2.4 in). The penis reaches adult size about five years later. A study done in 1996 found the mean length of an adult man's penis is 3.5 in (8.9 cm) when it is flaccid (, ) (not erect or hard). The average length of an erect penis is about 12.9 to 15 cm (5.1 to 5.9 in).

The testicles have two main jobs: to make hormones and sperm. The testicles make the hormone testosterone, which spreads around the body. This causes the changes in the body that make a boy grow into a man. Testosterone also makes a man feel like having sex. One year after puberty begins, when boys urinate (pee) after waking up in the morning, some sperm can be found in the urine. When a boy is about 13 years old his testicles will have grown to the stage that he may be fertile (able to make a woman pregnant). However, it will be still be difficult for him to do so. Boys usually only become fully fertile when they reach about 14 to 16 years of age. The sperm in the testicles mixes with other liquids in the body to form a whitish or yellowish and sticky fluid called semen. During puberty, two glands in the body called the seminal vesicles and prostate also grow bigger. These glands make a lot of the liquid that is in semen.

When a man is sexually excited, he gets an erection – his penis becomes bigger, longer and harder. A male can become sexually excited if thinks about sex or sees a good-looking person, or if his penis rubs against something. During puberty, some boys also have spontaneous erections. These are erections that happen by themselves without any reason. This can be embarrassing when it happens in a public place.

When a man's penis is sexually stimulated for some time, he has an orgasm and semen shoots out from the penis. This is called ejaculation. Boys who have not begun puberty cannot ejaculate. A boy's first ejaculation usually happens about one year after he begins puberty. For some boys, the first ejaculation takes place when they are sleeping. This is called a nocturnal emission or a wet dream. It happens without the boy's control, often when he is having a dream about sex. Scientists believe that wet dreams are the body's way of removing too much semen. A study done of 5,300 white men in the United States in 1948 found that 13% of them had their first ejaculation through a wet dream, This seems to tell us that most boys have their first ejaculation after masturbating. A male masturbates when he rubs his penis to make himself feel good sexually. The study also found that most boys who have their first ejaculation by masturbating do this a year or more earlier than boys who have their first ejaculation through a wet dream. A 2004 survey by a magazine in Canada found that most males (43%) started masturbating when they were about 12 to 13 years old. When a boy begins masturbating, wet dreams often stop happening because semen is taken out from his body regularly.

When a boy starts to ejaculate, he usually produces only a small amount of semen. The semen is different from what an adult man produces. It is usually clear and stays sticky. It either has no sperm in it, or sperm that do not move properly or do not move at all. A boy's semen only becomes like an adult man's semen about two years after his first ejaculation.

Body hair and skin changes

Not long after a boy's testicles and penis start to grow, pubic hair (, ) begins to appear. Pubic hair is hair that grows in the pubic region, which is the part of the body where the penis is. Pubic hair is shorter, curlier and rougher than hair on the head. It usually starts growing on the abdomen above the penis at the place where it joins the body. (The abdomen is the part of the torso where the navel or bellybutton is.) There may also be some hair on the scrotum. After about six months to a year, there will be a large triangle of hair in the pubic region. Within three to four years after puberty begins, there is a lot of pubic hair in the area above the penis. Later on, pubic hair also grows on the abdomen upwards towards the navel and on the insides of the thighs.

About two years after pubic hair starts to appear, hair also grows on other parts of the body:

In the armpits.
Around the anus.
On the upper lip, forming a mustache (also spelled moustache in the United Kingdom and other countries).
On the sides of the face in front of the ears, forming sideburns.
Around the nipples.
On the lower part of the face, forming a beard.

The hair on the arms, legs, chest, abdomen and back may also become thicker. Different men have different amounts of body hair. Many boys begin shaving when hair starts growing on their faces.

A larger amount of male hormones in the body cause changes to perspiration (sweat). This gives it a more "adult" body odor or smell. The hormones also cause sebaceous glands in the skin to make more sebum, a type of oil that keeps the skin from getting too dry. Sebum and dead skin cells can mix with a type of germ called bacteria and block pores (tiny openings) in the skin. This causes a skin problem called acne. Most people get acne during puberty. When a person has acne, he gets swellings on his skin called blackheads, whiteheads and pimples. Blackheads and whiteheads are painless, but pimples can be red and painful. They usually form on the face but can also appear on the neck, shoulders, upper back and chest. Oil glands on scalp – the part of the head on which hair grows – also make a lot of sebum. This can cause dandruff, in which small white bits of skin fall from the scalp.

Voice changes
During puberty, a boy's larynx or voicebox also grows larger. This makes the laryngeal prominence or Adam's apple – the lump that sticks out of the front of his neck – larger too. As the larynx grows the vocal folds become longer and thicker, so they vibrate (move back and forth) more slowly. This causes the voice to lower in pitch or tone and become deeper. When this happens, it is sometimes said that the boy's voice has "broken". However, it actually does not happen overnight but over some time. During this time, the voice may sound scratchy. On average, a boy's voice normally reaches its adult sound when he is around 15 years old.

Body growth
Towards the end of puberty, boys go through a "growth spurt" which lasts for about two to three years. During this time, their body grows taller very quickly. When the growth spurt is at its fastest point, some people grow  or more a year. This happens about two years after puberty starts, usually between the ages of 13 and 15. When a boy reaches the end of his growth spurt when he is about 18 years old, he will be at his adult height. His body will not grow much taller after that. Because of their growth spurt, boys' muscles can feel sore. These "growing pains" can feel worse if boys are active and do a lot of exercise. They go away after a while.

Boys grow more slowly than girls, but for a longer time. That is why most men are taller than women. By the end of puberty, adult males have heavier bones and more muscle than females. In an average adult man, muscle makes up 50% and fat 15% of his weight. On the other hand, 40% of an average adult woman's weight is made up of muscle while 27% is made up of fat. Because men have less body fat than women, their hips do not grow bigger. Some bones like those in the jaw and shoulders grow more in males than in females. That is why males have wider faces and shoulders but narrower hips.

Body changes in females
The changes in a girl's body during puberty usually take place between the ages of eight and 18 years. Most girls will have finished puberty around the age of 15. They will have breasts and pubic hair, will menstruate (have a period) every month, and will be able to get pregnant. They will usually also have reached their full adult height.

Breasts grow

When the breasts start to grow, this is normally the first sign of puberty that can be seen on the outside of a girl's body. This usually happens when girls are about the age of 10.5 years. A lump that is a bit hard appears in each breast under the areola, which is the dark ring around the nipple. The lump in one breast may grow before the other one. This is called breast budding. Within six to 12 months, both breasts will have started growing. The swelling can be felt and seen outside the edges of the areolae. About one and a half to two years after the breasts first start growing, they are close to the shape and size of an adult woman's breasts. The nipple and areola may be on a smaller mound on each breast. This small mound usually goes away when each breast is fully grown. Whether the breasts are small or large depends on how much fat there is in the body.

Body hair and skin changes

Between the ages of about eight and 14 (on average, at 11 or 12 years), pubic hair begins to grow along the labia (the "lips" of the vulva), usually a few months after the breasts start growing. At first the hair is thin and straight instead of curly, and there is not much of it. Within a year, the pubic hair becomes rough, dark and curly and grows in a triangle shape in the pubic region. About one year after pubic hair begins appearing, underarm hair also grows. The hair on the arms and legs also gets thicker, and some girls may have hair appearing on their upper lip and in front of their ears.

Like boys, higher amounts of hormones in the body cause girls' perspiration (sweat) to change. This gives them a more adult body odor or smell. The hormones also cause the skin to produce more sebum (oil), which usually leads to acne.

Changes to the sex organs and menstruation
When girls are between eight and 11 years old, the two ovaries in their body begin to grow bigger. Each ovary is egg-shaped, and is attached to the side wall of the pelvis. The pelvis is a large set of bones in the hips. The ovaries are organs that make female hormones. These hormones cause a girl to grow into a woman, and make her feel like a woman. The hormones also make it possible for females to become pregnant and have babies. Inside the ovaries are about 200,000 ova (egg cells). For a baby to be formed, a woman's ovum and a man's sperm must come together. During puberty, the ova also grow bigger.

Between the ages of nine and 15 years (on average, at 12 to 13 years), the vagina and uterus (womb) become bigger. The uterus is the organ in which a baby grows. The vagina is a tube leading from the uterus to the outside of the body. The opening of the vagina is inside the vulva, in between the legs. A clear or whitish fluid may start to flow out of the vagina to keep it clean. Then, about two years after the breasts start to grow, when a girl is between ten and 16 years old (on average, at 13 to 14 years), hormones made by her ovaries cause the ovaries to release an ovum, which moves into the uterus. Usually, only one ovum is released at a time. The hormones also tell the uterus to get ready for a baby, in case the ovum meets a sperm and gets fertilized. The walls of the uterus become thicker with extra tissue. Inside the thick part of the uterus are blood vessels and other nutrients that a baby will need to grow. If an ovum in the uterus gets fertilized, it sticks to the wall of the uterus and starts to grow. However, if the ovum is not fertilized, it does not stick. The uterus then gets rid of the ovum and the extra tissue by releasing it from the body. The tissue and blood flows out of the uterus through the vagina. This is called menstruation or having a period. The bleeding normally lasts for about three to five days, though some girls may bleed for longer or have a bit of bleeding between periods. The uterus then starts preparing for another ovum. For most girls, the time between their periods is about one month. For about two years after menstruation starts, the time between periods is not always the same. Some girls may skip a month, or have two periods close to each other. It is also normal to have cramps (rather painful squeezing feelings) or to feel bloated (swollen up) in the abdomen during periods. When many girls start having periods, they begin using sanitary napkins (also called sanitary pads) or tampons to soak up the blood and tissue. A sanitary napkin is a piece of material that is absorbent (able to take in liquids) which is worn between the vulva and underpants. A tampon is a stick of absorbent material that is placed inside the vagina.

In 2004, a survey by a Canadian magazine found that most females (25%) started masturbating when they were about 12 to 13 years old.

Body growth
Because of more hormones in the body, girls start to have more fat in their breasts, abdomen, hips and thighs. At the age of ten years, the average girl has 6% more body fat than the average boy, but by the end of puberty the difference is nearly 50%. The fat makes sure that a baby growing inside a pregnant woman will have enough nutrients. Also, the bones in the pelvis move further apart to make room for a larger uterus and ovaries, and so there is space for a baby to grow in the uterus and to pass out of the body when it is born. The extra fat and wider hip bones that girls have give them a curvier shape.

Girls also experience a growth spurt during puberty. In the first year after puberty begins, they grow about . They grow even faster the next year or so, then the growth slows down and almost stops when they start menstruating. After a girl's periods begin, she usually does not grow more than  taller.

Emotional changes in males and females
The large amounts of hormones in the bodies of boys and girls during puberty can also affect their emotions. Young people begin to be attracted by (drawn to) each other and thinking about what it is like to have sex. They are often worried about what other people think about them. They can also feel an urge to do things that are dangerous, such as taking drugs or too many alcoholic drinks, or smoking. They sometimes want more independence – more power to decide things for themselves – and can get angry when their parents do not allow them to do things. The brains of teenagers are still growing, and it may take a while before they are mature enough to know how to make good choices about their lives. Therefore, it may be helpful for them to follow the advice of adults they trust, even if it does not make much sense to them at the time.

Culture

Because puberty is the time in a child's life when he or she becomes able to make children, this is seen as very important. Therefore, people in many countries around the world practice Rites of passage to mark this change.

Males
Australia. Among some aboriginal tribes in Australia, when young men go through puberty, their penises are cut or pierced (something sharp is used to poke through the skin), or they may be circumcised. Circumcision is cutting off the foreskin of the penis (the piece of skin that covers the glans penis or head of the penis). Young men are also sent away from home to go on a long trip on foot called a walkabout. During this trip, they learn how to hunt animals and survive in the open.

Females

America. Among the Navajo (, ), who are a Native American people, a young woman who has had her first period goes through a four-day ceremony called Kinaalda which shows that she has changed from being a girl to a woman. The young woman's mother combs her hair and ties it into a ponytail. The young woman's family then sings a prayer, after which she puts on a dress made of a rug and jewellery made of turquoise and seashells. The young woman then runs as fast as she can towards the east, and turns around and runs home. She usually does this once in the morning and once in the evening every day during the ceremony. On the first night, the young woman does not go to sleep but stays awake while more prayers are sung. During the ceremony, the young woman also stands straight or lies on the ground in front of her mother, and her mother passes her hands over the young woman's body to make sure that she grows up beautiful. On the last day of the ceremony, the young woman does a final run; her mother passes her hands over her body one last time; and the young woman gives alkaan, a large cake made of maize (corn) that she has made, to her whole tribe to eat.
Brazil. Among the Urubu-Kaapor people of Brazil, South America, when a young woman has had her first period, she goes into a room in her home covered with palm leaves to spend time alone for a month. She only eats cooked white cassava flour and white tortoise meat. She sleeps in a hammock (a type of bed made of rope that is hung above the floor) as it is believed that some magic will escape if her feet touch the ground. On the seventh day of her time alone, the young woman's father cuts her hair very short. Her legs are scratched with the tooth of an agouti, which is an animal that looks like a guinea pig. Pieces of cloth are wrapped around the woman's forehead and abdomen (tummy), and large ants are put inside the cloth. After the woman has been bitten by the ants a few times, the cloth is removed. The Urubu-Kaapor people believe that the woman will learn how to be strong if she suffers some pain. After the young woman has finished spending a month alone in her room, she makes a meal and a special drink from cassava and gives it to her family and other people in her village. The young woman is now considered an adult, and can wear a necklace of feathers and a waistband with flowers. She also puts pink makeup made from plants on her face.
Ghana. When young women of some tribes in Ghana, Africa, have had their first period, they spend two to three weeks away from their family and friends. The queen mother of the town or village where they live and other older women teach the young women about sex and birth control. The young women also learn how to relate to men so that they can have a good marriage. After this, the young women appear at an event attended by the chief and everybody in the town or village. Young men also come to choose women to marry.

Notes

References

Further reading

Articles

Books

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Videos

Other websites
 Growing Up Sexually: A World Atlas 
 NIH guide to puberty and adolescence
 "Puberty in Girls" from AboutKidsHealth, The Hospital for Sick Children, Toronto, Canada 
 "Puberty in Boys" from AboutKidsHealth, The Hospital for Sick Children, Toronto, Canada 
 Teen Forums – Puberty

Physiology
Human sexuality