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.
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:
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:
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.
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).
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.
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.