Sex hormones are a group of steroid hormones that drive reproductive development, sexual function, and a surprisingly wide range of other processes throughout the body. The three main categories are estrogens, progesterone, and androgens (including testosterone). While people often associate estrogen with women and testosterone with men, all of these hormones are present and active in every human body, just in different amounts.
What Makes Sex Hormones Different From Other Hormones
Your body produces many types of hormones, from insulin (a protein hormone) to melatonin (derived from amino acids). Sex hormones belong to a third category: steroids. This matters because steroid hormones can pass directly through cell membranes and switch genes on or off inside the cell’s nucleus. That ability to reach deep into cells and alter gene activity is what gives sex hormones such powerful, body-wide effects on growth, metabolism, and tissue development.
Sex hormones can also act quickly by binding to receptors on the surface of cells, triggering rapid signaling cascades that influence enzymes, calcium channels, and other cellular machinery. This dual action, both fast signaling and slow gene regulation, explains why hormonal shifts can cause both immediate symptoms (like a hot flash) and gradual changes (like bone loss over years).
The Three Main Types
Estrogens
Estrogens are actually a family of three hormones. Estradiol is the strongest and most abundant during the reproductive years. It matures and maintains the reproductive system, drives the monthly release of an egg, and thickens the uterine lining to prepare for pregnancy. Estrone is a weaker estrogen produced by the ovaries, fat tissue, and adrenal glands. It becomes the dominant estrogen after menopause. Estriol is the third and weakest, playing a larger role during pregnancy.
Progesterone
Progesterone is released primarily by the corpus luteum, a temporary structure that forms in the ovary after an egg is released. Its main job is preparing and maintaining the uterine lining during the second half of the menstrual cycle. If pregnancy occurs, progesterone production ramps up significantly. During puberty, progesterone also contributes to breast development by increasing the number of milk-producing structures within the breast.
Androgens
Testosterone is the most well-known androgen, but it’s one of several. Others include DHEA (the main androgen made by the adrenal glands) and dihydrotestosterone, a more potent form that testosterone converts into within certain tissues. In males, androgens are essential for sperm production, muscle mass, and the development of male physical traits. In females, androgens serve as the raw material that the body converts into estrogen, and they independently contribute to bone health, sex drive, and metabolic regulation.
Where Sex Hormones Are Made
Three tissues do the heavy lifting. The testes produce testosterone through specialized cells called Leydig cells, which respond to signals from the brain’s pituitary gland. A small amount of testosterone is also converted to estrogen within the testes themselves.
The ovaries are the primary source of estradiol. They also contribute about 20% of a woman’s testosterone. The remaining testosterone in women comes from the adrenal glands (about 30%) and from conversion of other hormones in tissues like fat and skin (50% to 60%).
The adrenal glands sit atop the kidneys and produce DHEA in a layer called the zona reticularis. This adrenal androgen production begins around age 6 to 8, years before the gonads activate during puberty, in a process called adrenarche. The adrenal glands also produce roughly half of the body’s progesterone during the first half of the menstrual cycle, with the ovaries producing the other half.
How the Brain Controls Hormone Levels
Sex hormone production isn’t random. It’s tightly regulated by a feedback loop connecting the brain and the reproductive organs, known as the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus, a small region at the base of the brain, releases a signaling hormone called GnRH in rhythmic pulses. These pulses travel to the pituitary gland, which responds by releasing two hormones: LH and FSH. LH and FSH then travel through the bloodstream to the ovaries or testes and stimulate them to produce sex hormones and develop eggs or sperm.
The system self-regulates through feedback. When estrogen levels rise, the brain detects this and dials back GnRH pulses, which reduces LH and FSH, which in turn reduces estrogen production. This negative feedback keeps hormone levels within a functional range. There’s one important exception: in the late follicular phase of the menstrual cycle, rising estradiol actually triggers a surge of LH rather than suppressing it. This positive feedback switch is what triggers ovulation.
What Sex Hormones Do During Puberty
Puberty is when sex hormones transform the body most dramatically. The HPG axis, which has been mostly quiet since infancy, reactivates. GnRH pulses increase in frequency and strength, initially during sleep, eventually persisting throughout the day.
In girls, rising estradiol causes breast development (typically the first visible sign, around age 9 or 10), fat redistribution to the hips and breasts, growth of the reproductive organs, and bone maturation. Menstruation begins toward the end of puberty, around ages 12 to 13 in most developed countries. Progesterone production starts at that point, though levels tend to be low and irregular for the first few years.
In boys, testosterone drives testicular and penile growth, deepening of the voice as the larynx enlarges, and increased muscle mass. The growth spurt in both sexes results from sex steroids triggering a rise in growth hormone and its downstream growth factor, IGF-1, which directly stimulates bone growth. Pubic hair appears in both sexes during this time, initially fine and light, becoming coarser and darker as puberty progresses. Axillary, chest, and facial hair in boys typically follow about two years later. The adrenal androgens responsible for early pubic hair growth also cause increased skin oiliness, body odor, and acne.
Beyond Reproduction: Bones, Brain, and Heart
Sex hormones influence far more than the reproductive system. Estrogen plays a significant role in brain function, particularly in the hippocampus, the region central to memory. Elevated estrogen levels enhance memory retention, and estradiol stimulates the release of acetylcholine, a key neurotransmitter involved in learning. At a structural level, estrogen promotes the formation of new synaptic connections between brain cells, providing the scaffolding for these connections to mature. Estrogen also appears to protect neurons from damage caused by seizures, stroke, and neurodegenerative disease.
The cardiovascular system is also hormone-sensitive. Receptors for estrogen, progesterone, and androgens are found throughout the brain regions that regulate blood pressure. Premenopausal women show resistance to certain forms of experimentally induced high blood pressure that readily develop in males. This protection erodes during perimenopause, when estrogen levels become erratic, and disappears after menopause. This pattern helps explain why cardiovascular risk in women rises sharply after menopause.
How Hormone Levels Shift With Age
Hormone levels aren’t static across a lifetime. Women typically begin the transition to menopause during their mid to late 40s, a process called perimenopause that lasts roughly 4 to 5 years. Early in this transition, estradiol levels become erratic and can actually spike higher than normal. FSH begins rising intermittently as the brain tries to compensate for declining ovarian function. Progesterone decreases gradually and continuously. By late perimenopause, estradiol drops and stabilizes at lower levels, FSH and LH rise sharply, and menstrual cycles become increasingly irregular before stopping entirely.
In men, testosterone declines more gradually, typically beginning in the 30s or 40s, at a rate of about 1% to 2% per year. This slow decline means most men don’t experience an abrupt hormonal shift the way women do at menopause, though the cumulative effects over decades can include reduced muscle mass, lower energy, and changes in mood and sexual function.
Signs of Hormonal Imbalance
When sex hormones fall outside their functional range, the effects are often noticeable. Low testosterone in men can lead to reduced fertility, fatigue, loss of muscle, and decreased sex drive. In women, imbalances in estrogen and progesterone can disrupt menstrual cycles, affect mood, and contribute to bone thinning over time. Excess androgens in women can cause acne on the face, chest, or upper back, along with hair thinning on the scalp. These symptoms overlap with many other conditions, so patterns matter more than any single symptom.