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(December 5, 2010)

Girls and Puberty

Before we can understand the reasons why puberty is occurring earlier in girls than used to be the case, we need to take a few moments to discuss puberty itself: What is it? and When does it normally occur?

PUBERTY is the biological process during which a child's body becomes capable of sexual reproduction. As a general rule, puberty in girls runs from 10 to 16 years old, and in boys, from 12 to 17 years old — although, as you would expect, there are significant variations. During the 5-6 years it takes a child to pass through puberty, important changes occur in the child's body.

The goal of puberty is REPRODUCTIVE MATURITY, that is, changing the child's body into one that is capable of fertilizing or bearing a child of his or her own. In cultural terms, puberty overlaps adolescence, that is, the teenage years. Thus, we can also look upon puberty as the beginning of the process by which a child becomes a young adult.

Although puberty creates a lot of changes, most of them are internal to the child. From the outside, the most noticeable aspects of puberty are the development of the "secondary sex characteristics". To explain what that means, I need to digress briefly.

In mammals, the PRIMARY SEXUAL CHARACTERISTICS are the structures directly involved in reproduction, that is, the sex organs. In humans, the primary sexual characteristics are the uterus and ovaries (females) and the testes (males). The SECONDARY SEXUAL CHARACTERISTICS are the features that distinguish the two sexes of a particular species, but are not a direct part of the reproductive system.

In the animal kingdom, secondary sexual characteristics — especially in males — are often quite striking. For example, the male lion produces a mane, the male peacock develops long tail feathers, and the male deer grows antlers. In humans, there are a variety of secondary sexual characteristics, the most noticeable of which are enlarged breasts (females) and facial hair (boys).

Thus, one way to answer the question — at what age does puberty start? — is to observe the age at which these specific changes occur. For example, when do the secondary sexual characteristics begin to appear? If they happen earlier than used to be the case, we can say that puberty is starting earlier than it used to.

Puberty, as you can imagine (and as you may remember) is a very complicated process that plays out over 6-7 years. It starts with a process called ADRENARCHE, during which time the outside layer of the adrenal glands (which sit atop the kidneys) start secreting various hormones, in particular, DHEA (dehydroepiandrosterone), DHEA-S (DHEA sulfate), and androstenedione.


If you are like most people, hormones are mysterious substances with long incomprehensible names. Actually, that is true: hormones are mysterious substances with long incomprehensible names. However, the basic idea is simple.

A HORMONE is a substance that acts as a chemical messenger. Hormones are produced in various organs and then injected into the bloodstream, where they circulate throughout the body.

When a tiny drop of hormone encounters a part of the body that is sensitive to that hormone, it stimulates the nearby cells to react in a certain way. For example, the hormone insulin causes cells in the liver, muscles, and fatty tissue to extract sugar from the blood and store it for later use.

Within a year or two of adrenarche, a part of the brain called the hypothalamus, releases chemicals that trigger another part of the brain, the pituitary gland, to secrete two other important hormones: FSH (follicle-stimulating hormone) and LH (luteinizing hormone). The combined effects of FSH and LH is to initiate changes in the ovaries, a process referred to as GONADARCHE. The ovaries then start producing hormones of their own: primarily a type of estrogen called estradiol, along with a lesser amount of progesterone.

Within a few years, the growing amounts of hormones in a girl's body bring about the first signs of puberty. First, the estradiol stimulates the breast tissue, resulting in what is called THELARCHE, the first signs of breast development (the so-called breast buds). About a year later, the DHEA and DHEA-S cause the first appearance of pubic hair, referred to as PUBARCHE.

About a year after pubarche, the continued effects of estradiol will cause a girl to experience MENARCHE: her first menstrual period. After menarche, the menstrual cycle continues for about 35-40 years, until such time as the ovaries cannot produce enough hormones to support the cycle any longer.

I realize that all this can be a bit confusing. To help you put everything in perspective, the table below contains a summary of the various stages of puberty, along with the ages at which they take place. Please note that the ages are approximate, and there is significant variation. Moreover, as we will discuss presently, the age at which puberty starts has been decreasing, so these numbers have actually gone down over the years. For example, in 1850, the average age of menarche of Western European girls was 17.

Stages of Puberty in Girls

StageDescriptionApproximate Age of Onset
AdrenarcheAdrenal gland activity7 years old
GonadarcheChange in ovaries8 years old
ThelarcheBreast development11 years old
PubarcheAppearance of public hair12 years old
MenarcheFirst menstrual cycle13 years old

The most common markers used when talking about the timing of female puberty are thelarche (breast development) and menarche (start of menstruation).[16] [17] Thus, it makes sense for us to ask the question: Do girls experience thelarche and menarche earlier in life than used to be the case?

As we will see, this is indeed the case, indicating that puberty, in general, is occurring earlier and earlier — which means that the age at which young girls really, really, really want their own phones is also decreasing.

Menarche and Menopause

As we discussed, the date of a girl's first period is called menarche. The date of a woman's last menstrual flow is called MENOPAUSE. The time of transition surrounding the menopause, when a women may experience a variety of symptoms, is called CLIMACTERIC.

You will, of course, hear many people refer to this time of life as menopause. Strictly speaking, however, "menopause" refers only to the cessation of the menses; the more exact term is "climacteric". In other words, menopause is to climacteric, as menarche is to puberty.

Hint for men: Whenever you hear middle-aged women talking about menopause, you can make it a point to correct them. ("Actually, it's not menopause; it's climacteric.") No doubt they will thank you graciously for setting them straight.

Jump to top of page


1. Introduction
2. A Word From Our Sponsor
3. The Female and Male Brains
4. Excessive Text Messaging
5. The Female Brain and Puberty
6. Introducing The Pleasure Center
7. Why Is It So Hard To Quit
8. Girls and Puberty
9. Girls and Premature Puberty
10. Why Your 10 Year Old Daughter Wants Her Own Phone
11. A Final Note
12. References