The change that takes place when childhood passes into manhood or womanhood. This change is generally a very definite one, occurring at about the age of 11–13 years, although it is modified by race, climate, and bodily health so that it may appear a year or two earlier or several years later. At this time, the sexual functions attain their full development; the contour of the body changes from a childish to a more rounded womanly, or sturdy manly, form; and great changes take place in the mode of thought and feeling.

In girls, puberty is marked by the onset of MENSTRUATION and development of the BREASTS. The latter is usually the first sign of puberty to appear, and may occur from nine years onwards; most girls show signs of breast development by the age of 13. The time from the beginning of breast development to the onset of menstruation is usually around two years but may range from six months to five years. The first sign of puberty in boys is an increase in testicular and penile size (see TESTICLE; PENIS) between the age of ten and 14. The LARYNX enlarges in boys, so that the voice – after going through a period of ‘breaking’ – finally assumes a deep pitch. Hair appears on the pubis and later in the armpits in both boys and girls, whilst in the former it also begins to grow on the upper lip; skin eruptions are common on the face (see ACNE). Disorders – both delayed and premature puberty – are dealt with by paediatric endocrinologists to determine if there is a treatable hormonal problem or just an extreme of normal variation.