secondary sex character

secondary sex character, physical feature related to the sex of an organism that emerges during puberty, or the phase of sexual maturity. Examples of secondary sex characters in humans include the development of breasts in females and pigmented facial hair in males. Secondary sex characters are distinguished from primary sex characters, which are present at birth and are comprised of the external and internal genitalia, including the penis and testes in males and the vagina and ovaries in females.

In human females, prepubescent changes involving secondary sex characters include the rounding of the hips and the first phase of breast development. The latter begins with an elevation of the areola surrounding the nipple; this slight swelling is caused by the growth of a small conelike structure known as the breast bud. In both sexes the onset of puberty coincides with the appearance of pubic hair, and this period ends when pubic hair development is complete.

During puberty, females experience increased breast development, with the breast buds enlarging to form the primary breast. In males, the voice deepens and pigmented axillary and facial hair appear, usually about two years after the emergence of pubic hair. Changes in primary and secondary sex characters are essentially complete by postpubescence, at which time the individual is fertile. Nonetheless, some changes in secondary sexual characters continue to occur in this phase. For instance, males may begin to grow a beard, and females may experience further breast development.

The timing of and patterns in the development of secondary sex characters vary markedly between individuals, often in parallel with variations in the onset of puberty. Such variations are influenced by a range of factors, including body mass index, ethnicity, and genetics.