Developmental stages

thumb|right|Тhe changes in ovarian hormones throughout the human lifespan. During childhood, hormone levels are low. During puberty, estrogen begins to fluctuate, followed by progesterone when you first begin ovulating. After 6-12 years the menstrual cycle normalizes into a rhythm during the menstrual years, barring any reproductive health issues or pregnancy and breastfeeding, which pauses the cycling. Perimenopause, similar to puberty, has high fluctuations of estrogen as progesterone slowly begins to decline. Eventually, a person stops ovulating, reaches menopause, and hormones return to ch

Menarche ( ; ) is the first menstrual cycle, or first menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility. Girls experience menarche at different ages, but the most common age is 12. Having menarche occur between the ages of 9–14 in the West is considered normal.

thumb|Tanner scale of female breast development Thelarche, also known as breast budding, is the onset of secondary breast development, often representing the beginning of pubertal development. It is the stage at which male and female breasts differentiate due to variance in hormone levels; however, some males have a condition in which they develop breasts, which is called gynecomastia. Thelarche typically occurs between the ages of 8 and 13 years with significant variation between individuals. However, the initial growth of breast tissue occurs during fetal development. It is usually the first

Pubarche () refers to the first appearance of pubic hair at puberty. It is one of the earliest physical changes of puberty and can occur independently of complete puberty. It is usually the second sign of puberty, after thelarche in females and gonadarche in males (though in females, it can also happen before thelarche, but this is less common).

Spermarche, also known as semenarche, is the time at which a male experiences his first ejaculation. It is considered to be the male counterpart of menarche in females. Depending on upbringing, cultural differences, and prior sexual knowledge, males may have different reactions to spermarche, ranging from fear to excitement. Spermarche is one of the first events in the life of a male leading to sexual maturity. It occurs at the time when the secondary sex characteristics are just beginning to develop. Researchers have had difficulty determining the onset of spermarche because it is reliant on

Adrenarche is an early stage in sexual maturation that happens in some higher primates (including humans), typically peaks at around 20 years of age, and is involved in the development of pubic hair, body odor, skin oiliness, axillary hair, sexual attraction/sexual desire/increased libido and mild acne. During adrenarche the adrenal glands secrete increased levels of weak adrenal androgens, including dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and androstenedione (A4), but without increased cortisol levels. Adrenarche is the result of the development of a new zone o

Gonadarche () refers to the earliest gonadal (reproductive gland) changes of puberty. In response to pituitary gonadotropins, the ovaries in females and the testes in males begin to grow and increase the production of the sex steroids, especially estradiol and testosterone. The ovary and testis have receptors, follicle cells and leydig cells, respectively, where gonadotropins bind to stimulate the maturation of the gonads and secretion of estrogen and testosterone. Certain disorders can result in changes to timing or nature of these processes.

Somatopause is the progressive decline in the levels of growth hormone (GH) and insulin-like growth factor 1 (IGF-1), hormones of the hypothalamic–pituitary–somatotropic axis (HPS axis), with age. Secretion of GH may only be 60% of that of a young adult by age 70 years. Somatopause results in changes in the body, such as body composition changes like a decrease in lean body mass. Estrogens and progesterone may oppose somatopause by increasing GH and IGF-1 levels.