Puberty marks the beginning of adolescence. It consists of two to four years of rapid growth and development leading up to physical maturity and the ability to reproduce.


The first thing to realize is that there is a wide age range at which puberty begins. The largest number of girls begin their development at around the age of ten and have their first period at about twelve and a half. It’s not abnormal for girls to start at nine; some may start even earlier. Breast development may not begin until as late as twelve or thirteen, in which case the first menstrual period may not come until fourteen of fifteen.

The average boy starts puberty two years later than the average girl, at around twelve; some healthy boys start as late as fourteen or fifteen. Assessment of pubertal development should be a part of the annual checkup for teens. If puberty starts either very early or very late, the doctor or nurse practitioner needs to make sure that there is no medical condition causing the unusual timing.


The earliest changes of puberty occur deep inside the brain. Hormones flow from the brain through the bloodstream to the gonads (testicles or ovaries), switching them into high gear. The gonads in turn produce the main sex hormones, testosterone and estrogen, that trigger the rest of puberty. What exactly sets the brain into action in the first place, no one knows for sure.

Heredity, nutrition, and general health all influence the timing of puberty. In the United States, improved (or, at least, increased) nutrition during childhood has lowered the age of puberty by several years, and there is controversy about whether other factors, such as pesticides or hormones in foods, may also play a role.

Puberty development in girls

Let’s trace what happens to the average girl who starts puberty at age ten. When she was seven years old, she was growing two to two and a half inches a year. When she was 8, her rate of growth slowed down to perhaps one and three-quarter inches a year. Nature seemed to be putting on the brakes. Suddenly, at about ten, the brakes let go, and she begins to shoot up at the rate of three to three and a half inches a year for the next two years. Instead of putting on five to eight pounds a year, as she used to, she now gains from ten to twenty pounds a year. Her appetite increases significantly to make this gain possible.

Other things are happening, too

At the beginning of this time, her breasts begin to develop. The first thing noticed is a hard lump under the nipple. This may be frightening to parents because of the fear of breast cancer, but it is the normal onset of breast development. For the first year menstrual period nears, it rounds out into more nearly a hemisphere. Occasionally, one breast begins to develop months before the other. This is fairly common and nothing to worry about. The earlier developing breast tends to stay larger through puberty and may on occasion remain so permanently.

Soon after the breasts begin to develop, pubic hair starts to grow. Later, hair appears in the armpits. The hips widen. The skin texture changes. At twelve and a half, the average girl has her first menstrual period. This event is called menarche. By now her body has begun to look more like a woman’s. From this time on, her growing slows down rapidly.

In the year after her first period she will grow perhaps one and a half inches; in the year after that, perhaps three-quarters of an inch. In many girls menstrual periods are irregular and infrequent for the first year or two. This is not a sign that something is wrong; it only shows that full maturity was not reached at the time of the first period.

There is no one age at which puberty begins; each girl has an individual maturational rate and timetable. That a girl starts puberty much earlier or later than average usually doesn’t mean that her glands aren’t working right. It means only that she is on a faster or slower timetable. This individual timetable seems to be an inborn trait: parents who were early developers and the same holds for late developers. The 13-year-old who has shown no signs of pubertal development can be assured that she will develop, even though it may take her longer to do so.

There are other variations besides the age at which puberty development begins. In some girls, pubic hair appears months before the breasts start to develop. And once in a while, hair in the armpits is the earliest sign of change instead of a late one. The length of time between the first signs of puberty development and the coming of the first period is usually about two and a half years. If a girl has been fully mature for over two years or is over sixteen and has not had her first period, she should be evaluated by her physician.

It can be upsetting if the onset of puberty is later or earlier than average. The girl who begins puberty at eight may feel awkward and self-conscious when she finds herself the only girl in her class who’s shooting upward and acquiring the shape of a woman. The responses of teachers, parents, and peers can also be confusing. Also bothered is the girl who’s on a slow timetable. The 13-year-old who has shown no signs of puberty development may think she’s abnormal. Reassurance from her doctor may be helpful.

Puberty development in boys

The average boy begins two years later than the average girl, at 12 in contrast to her ten. The earlier developers among boys begin as early as 10, a few younger still. Plenty of slow developers start as late as 14, and there are a few who wait longer.

Pubic hair begins to grow first, then the testicles grow, and finally the penis begins to increase, first in length, then in diameter. All these events before the growth spurt, and may be known only to boy himself (in contrast to a girl’s development, where the first sign of puberty, breast development, is obvious to others).

During puberty, a boy may grow in height at double the rate as before. Height often increases first, along with arm length and shoe size, giving the early adolescent boy a gangly, uncoordinated look. The muscles fill in later, creating more of a manly shape.

At about the same time, the hair in the armpits and on the face grows thicker and longer. Then the voice cracks and deepens. In some boys, a small area under the breast nipples enlarges and may become tender; this is normal. In a few, the breasts enlarge enough to cause embarrassment and worry. This occurs more often in boys who are overweight. Medical reassurance can be helpful.

After about two years, the boy’s body has pretty much completed its transition. In the following few years he will continue to grow more slowly, finally stopping at around eighteen. Some later-developing boys will continue to grow even into their early twenties. Early pubertal development in boys is seldom upsetting; for a couple of years, an early-developing boy may be the tallest and strongest in the class (though very early development, before about age ten, should be evaluated medically).

Late development, on the other hand, can be very upsetting. The boy who is on a slow timetable of development, who is still a “shrimp” at 14 when most of his friends have turned almost into grown men, usually needs reassurance, and sometimes counseling, to help him cope. Size, physique, and athletic ability count for a lot at this age.

Some parents, instead of reassuring their son that he will develop in time and grow 8 or 9 inches in the process, take him on a hunt for a doctor who will give him growth hormone treatment. This only convinces him that something is really wrong with him. True, there are hormone preparations that bring on the signs of puberty at whatever age they are given.

However, there is no evidence that long-term psychological benefits will follow, and these treatments may cause a boy to end up shorter than he normally would be by prematurely stopping his bone growth. For the rare occasion when there may be too little or too much growth hormone production, a pediatric endocrinologist (hormone specialist) should be consulted before any decision is made about giving hormones.