Puberty involves a series of hormonally directed changes in a girl’s body and brain. Although many people think of puberty as an event marked by the first menstrual period, the term in fact refers to the entire developmental sequence that leads to sexual and reproductive maturity. Its physical signs include accelerated growth, breast development, pubic and axillary (armpit) hair growth, and the body odor that results from the activation of apocrine glands in those areas. The first menstrual period occurs near the end of this process. This entire progression usually takes about four and a half years, although some girls go through it more rapidly than others. (The range is from one and a half to six years.)

What You Need to Know

Breast budding is the first stage of breast development. The nipples can become very sore during this time. Reassurance that this is normal will help to decrease the pain, as will following a good diet. Following breast budding, the areolae widens then the breast enlarges under the nipple area. Though one breast will always be slightly larger than the other. Some girls have remarkable asymmetry, but it may take several years before the breasts are approximately the same size. It’s possible for breast growth to continue until a girl is eighteen or so, though she usually reaches her adult breast size within a couple of years after her first period.

In addition to breast budding and the growth of pubic hair, a girl’s adolescent body goes through major changes in composition. Both her lean body mass and total body fat increase, and her body fat percentage also increase from its prepubertal level. This results in part from a complex change in the interaction between estrogen and leptin, a hormone produced by fat cells that helps regulate their metabolism. Much of this new fat goes to her buttocks and hips.

In the months prior to their first period, it is common for girls to develop a vaginal discharge that is clear, white, or slightly yellow. This discharge is the result of increased vaginal secretions stimulated by estrogen. This frightens many girls and some are even concerned they have developed cancer. This is why, even in the best of circumstances, some anxiety during puberty is normal and to be expected.

The blossoming of sexual desire and interest is also perfectly natural at this stage. And so is masturbation. But if a child has been taught that sexual feelings are dirty or shameful, she may interpret this to mean that she herself is bad or shameful.

The Biology Behind the Changes

The changes of puberty begin in the brain. Starting at about age ten or eleven, two hormones known as gonadotropins—LH (luteinizing hormone) and FSH (follicle-stimulating hormone) become elevated to the same high levels seen in a postmenopausal woman. The elevation of these hormones begins several months before the beginning of breast development when the hypothalamus starts to release pulses of gonadotropin-releasing hormone. This, in turn, signals the pituitary gland to release FSH and LH, which tell the ovarian follicles to begin developing and producing estrogen and testosterone. It is estrogen that stimulates breast development, bone growth, and female fat distribution, while testosterone stimulates the sex drive and the increased sebaceous-gland secretions that can lead to acne.

Once the critical threshold of physical growth has been achieved, the central mechanism in the brain that controls the onset of puberty can be activated by the production of estrogen, regardless of its source. Since fat cells produce estrogen, girls who have a higher percentage of body fat usually begin the process of puberty earlier than the average. They also reach menarche, the first menstrual cycle, earlier. (For reasons that are probably related to the secretion of melatonin, so do girls who are blind.)

It takes a while for regular ovulation to become established. In the meantime, a girl’s periods are usually anovulatory and can be irregular or heavy. It’s common for 25 to 50 percent of adolescent girls to still have some anovulatory periods four years after menarche.

There is a wide range of differences in how girls go through puberty. Some speed through the process quickly, while others seem to hang on to childhood as long as possible, then suddenly blossom at the age of sixteen, long after everyone else. Yet for all its twists and turns, puberty is a normal life process that seldom requires medical attention.

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