This is the 2007 version. Click here for the 2017 chapter 16 table of contents.


Around the age of 9-10 in girls, later in boys, appear early signs of secondary sex characteristics appear. These are associated with hormones secreted in adolescence. In girls, the first pre-pubertal changes are the beginnings of breast development and pubic hair. In boys, the genitals increase in size and pubic hair appears, although it is not true pubic hair (coarse and pigmented) until between 13-16 years of age.

Other secondary sex characteristics in males, emerging between the ages of 10 and 16, are body growth and a deepening voice. The prostate glands also mature during this time so the ejaculation of fluids may accompany orgasm, although in young adolescents the sperm may be immature and infertile.

What are secondary sex characteristics? What can delay onset of menstruation?

The average age of menarche (onset of menstruation) is about 12.5 years old. There are great variations; some girls begin to menstruate when they are 10, others when 16 or older. Menstruation may be delayed in girls who are thin and exercise vigorously. For example, in a study of 89 ballerinas averaging 16 years old, 20 had not yet menstruated. Among those who had menstruated, the average age of menarche was 13.5, a year later than average (Frisch, 1980).

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