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Puberty is the passage from infancy to adulthood; it takes place in several stages, and is subject to complex neuro-endocrinological regulation, the progression of which is predetermined at the fetal stage. The mechanisms by which living creatures pass from one stage to another in the process of puberty are not completely understood even today.  Most of the mechanisms that control puberty have a cerebral and hormonal origin, in which the hypothalamus and the pituitary gland play a major role.  The hormonal production that is carried out by the hypothalamus and the pituitary gland leads to the activation of the gonads, that is, the testicles of males and the ovaries of females. Puberty thus results from the activation of the function of the hypothalamus, the pituitary gland, and the gonads, leading to the production of testosterone in males and different forms of estrogen in females.  This process leads to the complete development of sexual characteristics. Both males and females reach their maximum height; males become able to procreate, and females become fertile. In human beings, this system undergoes a first phase of activity in the fetus, and another phase in the first few weeks after birth, then going dormant during all of the period of infancy, reawakening only during puberty.

The onset of puberty takes place under the influence of a certain number of factors, of which the most important are genetic in nature; these genetic factors act as an internal biological clock.  Under these influences, the hypothalamus will increase the amount of the hormone GnRH (Gonadotropin releasing hormone) that it secretes; this secretion occurs in spurts (pulsatile secretion), which gradually increase in frequency and intensity. This allows the maturation of the pituitary gland, with pulsatile secretion of gonadotropins as well, LH (luteinizing hormone) and FSH (follicle stimulating hormone). These hormones are released to circulate in the body, and they affect the gonads, regulating their development as well as the secretion of gonadic steroids. These steroidal hormones promote the growth of secondary sexual organs, including the characteristics of sexual dimorphism related to the femaleness or maleness of hormones, for example, the gender related distribution of fatty tissue, the development of breasts, the increase in muscle mass, and changes in the pitch of the voice. However, males are not completely lacking in the female hormones (estrogens), which have important effects upon their bones and their brains.  Similarly, females produce small amounts of male hormones.