Humans use a sexual mode of reproduction. Reproductive phase is the phase in the life of every individual which makes the individual capable of reproducing the offspring. In the early reproductive phase, individuals acquire changes in the body which result in the formation of germ cells. Sperms are male germ cells and eggs are female germ cells. Reproductive phase involves the changes in appearance and size of the bodily organs.

Adolescence is the period of life that leads to sexual maturity. During this period of life, one can observe many changes in the body. Puberty is the period at the beginning of adolescence when the sex glands in a boy and a girl are capable of reproduction. Different changes in boys include change in the voice, active functioning of sweat and sebaceous glands, growth of facial and body hair, enlargement of penis etc. Different changes in girls include growth of pubic hair, active functioning of sweat and sebaceous glands, menstrual cycle, enlargement of breasts.