The three types of oestrogen — and which one matters most

Oestrogen is not a single hormone. It is a family of steroid hormones produced from cholesterol, sharing a similar structure but differing in potency and function.

Oestradiol (E2) — the most potent and most relevant form in women of reproductive age. Produced primarily by the ovaries. Responsible for the majority of oestrogen's effects on the brain, bones, cardiovascular system, skin and reproductive tissues. When people refer to "oestrogen" in the context of the menstrual cycle, they almost always mean oestradiol.

Oestrone (E1) — the predominant oestrogen after menopause. Produced mainly in adipose tissue through conversion of androgens via aromatase. Less potent than oestradiol. The reason body fat influences hormonal health — more adipose tissue means more aromatase activity and more oestrone production.

Oestriol (E3) — the weakest of the three. Produced in significant quantities only during pregnancy, by the placenta. Plays a role in maintaining pregnancy and has some clinical applications in hormone replacement but is not a significant factor in the menstrual cycle.

What is oestrogen?
Oestrogen is a group of steroid hormones — primarily oestradiol (E2) — produced mainly in the ovaries. Oestradiol is the dominant form in reproductive-age women and has receptors in virtually every tissue in the body. It regulates the menstrual cycle, supports bone density, cardiovascular health, brain function, mood, skin and libido.

What oestrogen does — tissue by tissue

The brain. Oestrogen crosses the blood-brain barrier and has profound effects on neurotransmitter systems. It upregulates serotonin receptors and supports serotonin synthesis — which is why mood, emotional resilience and social motivation are highest in the follicular and ovulatory phases when oestrogen peaks. It also supports dopamine pathways, acetylcholine production (memory and cognitive function) and BDNF (brain-derived neurotrophic factor — the protein responsible for neuroplasticity and learning). Read more about why you feel like a different person every two weeks.

The bones. Oestrogen prevents osteoclast activity — the process by which bone is broken down and resorbed. Without adequate oestrogen, bone turnover accelerates and bone density decreases. This is the primary mechanism behind the accelerated bone loss of menopause. In reproductive-age women, adequate oestrogen across the cycle maintains the bone density built during puberty.

The cardiovascular system. Oestrogen supports HDL (protective cholesterol), reduces LDL (harmful cholesterol), maintains blood vessel flexibility and has anti-inflammatory effects on the arterial wall. This is why cardiovascular disease risk increases significantly after menopause when oestrogen drops permanently.

The skin. Oestrogen stimulates collagen production and hyaluronic acid synthesis — the compounds responsible for skin thickness, elasticity and moisture retention. The skin changes of perimenopause and menopause — thinning, dryness, loss of elasticity — are directly driven by declining oestrogen. Even across the cycle, many women notice skin quality changes that track with their hormonal phase.

Muscle. Oestrogen supports muscle protein synthesis alongside its more celebrated co-factor, testosterone. The anabolic environment of the follicular phase — when both oestrogen and testosterone are elevated — is the most productive window for building and maintaining muscle. Read more about how hormones affect training in women.

What does oestrogen do in women?
Oestrogen supports serotonin and dopamine in the brain, prevents bone resorption, maintains cardiovascular health, stimulates collagen production in skin, supports muscle protein synthesis alongside testosterone, regulates the menstrual cycle and ovulation, and maintains libido and sexual function. Its receptors exist in virtually every tissue — it is a whole-body hormone, not a reproductive one.

Oestrogen across the cycle — your monthly map

Understanding when oestrogen rises and falls gives you a predictive map of your own energy, mood and performance.

Menstrual phase (Days 1 to 5): Oestrogen is at its lowest. Serotonin and dopamine support is minimal. The nervous system turns inward — making this a natural time for reflection, honest self-assessment and rest rather than output.

Follicular phase (Days 6 to 13): Oestrogen rises steadily. Energy, motivation, cognitive flexibility and mood rise with it. This is your biological spring — the phase where starting new projects, increasing training intensity and social engagement all feel natural and productive. Read more about the follicular phase.

Ovulatory phase (Days 14 to 16): Oestrogen peaks. Alongside a brief testosterone peak, this produces the highest verbal fluency, confidence, social drive and physical performance of the month. Use this window deliberately. Read more about the ovulatory phase.

Luteal phase (Days 17 to 28): Oestrogen falls after ovulation, rises slightly in mid-luteal, then drops sharply before menstruation. The premenstrual drop — particularly the final 4 to 6 days — takes serotonin with it, producing the emotional vulnerability of the premenstrual week. Read more about the luteal phase.

When does oestrogen peak in the menstrual cycle?
Oestrogen peaks twice — the first and largest peak occurs around ovulation (days 12 to 14), producing the mid-cycle surge in energy, confidence and mood. A smaller secondary peak occurs in the mid-luteal phase around days 20 to 22. Oestrogen is lowest during menstruation and drops sharply in the late luteal phase before the next period begins.
Does oestrogen affect mood?
Yes — directly and measurably. Oestrogen upregulates serotonin receptors and supports serotonin synthesis. When oestrogen is high, serotonin is well-supported and mood, resilience and social motivation are elevated. When oestrogen drops before menstruation, serotonin falls with it — producing the emotional vulnerability of PMS. This is neurochemistry, not psychology.