puberty puberty puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. it is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. in response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed. before puberty, the external sex organs, known as primary sexual characteristics, are sex characteristics that distinguish boys and girls. puberty leads to sexual dimorphism through the development of the secondary sex characteristics, which further distinguish the sexes. "sexual development" redirects here. for sexual development of non-human organisms, see sexual maturity. part of a series onhuman growthand development stages gamete zygote embryo fetus infant toddler child preadolescent adolescent emerging and early adulthood young adult middle adult old adult dying biological milestones fertilization pregnancy childbirth walking language acquisition puberty menopause ageing death development and psychology pre- and perinatal infant and child nature versus nurture adolescent youth young adult adult maturity developmental stage theories attachment ecological psychosocial psychosexual development moral cognitive cultural-historical evolutionary psychology portal on average, girls begin puberty at ages 10–11 and complete puberty at ages 15–17; boys generally begin puberty at ages 11–12 and complete puberty at ages 16–17. the major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average between ages 12 and 13. for males, first ejaculation, spermarche, occurs on average at age 13. in the 21st century, the average age at which children, especially girls, reach specific markers of puberty is lower compared to the 19th century, when it was 15 for girls and 17 for boys (with age at first periods for girls and voice-breaks for boys being used as examples). this can be due to any number of factors, including improved nutrition resulting in rapid body growth, increased weight and fat deposition, or exposure to endocrine disruptors such as xenoestrogens, which can at times be due to food consumption or other environmental factors. however, more modern archeological research suggests that the rate of puberty as it occurs now is the intended way. growth spurts began at around 10–12, but markers of later stages of puberty such as menarche had delays that correlated with severe environmental conditions such as poverty, poor nutrition, air and pollution. puberty that starts earlier than usual is known as precocious puberty, and puberty which starts later than usual is known as delayed puberty. notable among the morphologic changes in size, shape, composition, and functioning of the pubertal body, is the development of secondary sex characteristics, the "filling in" of the child's body; from girl to woman, from boy to man. derived from the latin puberatum (age of maturity), the word puberty describes the physical changes to sexual maturation, not the psychosocial and cultural maturation denoted by the term adolescent development in western culture, wherein adolescence is the period of mental transition from childhood to adulthood, which overlaps much of the body's period of puberty. differences between male and female puberty approximate outline of development periods from childhood to early adulthood. puberty is marked in green at right. 1 follicle-stimulating hormone – fsh 2 luteinizing hormone – lh 3 progesterone 4 estrogen 5 hypothalamus 6 pituitary gland 7 ovary 8 pregnancy – hcg (human chorionic gonadotropin) 9 testosterone 10 testicle 11 incentives 12 prolactin – prl two of the most significant differences between puberty in girls and puberty in boys are the age at which it begins, and the major sex steroids involved, the androgens and the estrogens. although there is a wide range of normal ages, girls typically begin puberty around ages 10–11 and end puberty around 15–17; boys begin around ages 11–12 and end around 16–17. girls attain reproductive maturity about four years after the first physical changes of puberty appear. in contrast, boys accelerate more slowly but continue to grow for about six years after the first visible pubertal changes. any increase in height beyond the post-pubertal age is uncommon. for boys, the androgen testosterone is the principal sex hormone; while testosterone is produced, all boys' changes are characterized as virilization. a substantial product of testosterone metabolism in males is the estrogen estradiol. the conversion of testosterone to estradiol depends on the amount of body fat and estradiol levels in boys are typically much lower than in girls. the male "growth spurt" also begins later, accelerates more slowly, and lasts longer before the epiphyses fuse. although boys are on average 2 centimetres (0.8 in) shorter than girls before puberty begins, adult men are on average about 13 centimetres (5.1 in) taller than women. most of this sex difference in adult heights is attributable to a later onset of the growth spurt and a slower progression to completion, a direct result of the later rise and lower adult male levels of estradiol. the hormonal maturation of females is considerably more complicated than in males. the main steroid hormones, testosterone, estradiol, and progesterone as well as prolactin play important physiological functions in puberty. the production of gonadal steroids in girls starts with production of testosterone, which is typically quickly converted to estradiol inside the ovaries. however the rate of conversion from testosterone to estradiol (driven by fsh/lh balance) during early puberty is highly individual, resulting in very diverse development patterns of secondary sexual characteristics. production of progesterone in the ovaries begins with the development of ovulatory cycles in girls (during the lutheal phase of the cycle), before puberty low levels of progesterone are produced in the adrenal glands of both boys and girls. estradiol levels rise earlier and reach higher levels in women than in men. while estradiol promotes growth of the breasts and uterus, it is also the principal hormone driving the pubertal growth spurt and epiphyseal maturation and closure. puberty onset puberty is preceded by adrenarche, marking an increase of adrenal androgen production between ages 6–10. adrenarche is sometimes accompanied by the early appearance of axillary and pubic hair. the first androgenic hair resulting from adrenarche can be also transient and disappear before the onset of true puberty. the onset of puberty is associated with high gnrh pulsing, which precedes the rise in sex hormones, lh and fsh. exogenous gnrh pulses cause the onset of puberty. brain tumors which increase gnrh output may also lead to premature puberty. the cause of the gnrh rise is unknown. leptin might be the cause of the gnrh rise. leptin has receptors in the hypothalamus which synthesizes gnrh. individuals who are deficient in leptin fail to initiate puberty. the levels of leptin increase with the onset of puberty, and then decline to adult levels when puberty is completed. the rise in gnrh might also be caused by genetics. a study discovered that a mutation in genes encoding both neurokinin b as well as the neurokinin b receptor can alter the timing of puberty. the researchers hypothesized that neurokinin b might play a role in regulating the secretion of kisspeptin, a compound responsible for triggering direct release of gnrh as well as indirect release of lh and fsh. effects of early and late puberty onset several studies about puberty have examined the effects of an early or a late onset of puberty in males and females. in general, girls who enter puberty late experience positive outcomes in adolescence and adulthood, while girls who enter puberty early experience negative outcomes. boys who have earlier pubertal timing generally have more positive outcomes in adulthood but more negative outcomes in adolescence, while the reverse is true for later pubertal timing. girls outcomes have generally indicated that early onset of puberty in girls can be psychologically damaging. the main reason for this detrimental effect is the issue of body image. as they physically develop, gaining weight in several areas of the body, early-maturing girls usually look larger than girls who have not yet entered puberty. a result of the social pressure to be thin, the early-maturing girls develop a negative view of their body image. in addition, people may tease the girls about their visible breasts, forcing the early-maturing girl to hide her breasts by dressing differently. embarrassment about a more developed body may also result in the refusal to undress for gym. these experiences lead to lower self-esteem, more depression and poorer body image in these early-maturing girls. furthermore, as physical and emotional differences set them apart from people in their same age group, early-maturing girls develop relationships with older people. for instance, some early-maturing girls have older boyfriends, "attracted to the girls' womanly physique and girlish innocence." while having an older boyfriend might improve popularity among peers, it also increases the risk of alcohol and drug use, increased sexual relations (often unprotected), eating disorders and bullying. generally, later onset of puberty in girls produces positive outcomes. they exhibit positive behaviors in adolescence that continue to adulthood. boys in the past, early onset of puberty in boys has been associated with positive outcomes, such as leadership in high school and success in adulthood. however, recent studies have revealed that the risks and problems of early maturation in males might outweigh the benefits. early-maturing boys develop "more aggressive, law-breaking, and alcohol abusing" behaviors, which result in anger towards parents and trouble in school and with the police. early puberty also correlates with increased sexual activity and a higher instance of teenage pregnancy, both of which can lead to depression and other psychosocial issues. however, early puberty might also result in positive outcomes, such as popularity among peers, higher self-esteem and confidence, as a result of physical developments, such as taller height, developed muscles, muscular male breast and better athletic ability. on the other hand, late-maturing boys develop lower self-esteem and confidence and generally have lower popularity among peers, due to their less-developed physiques. also, they experience problems with anxiety and depression and are more likely to be afraid of sex than other boys. changes in males