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Chemical structure of different forms of estrogen in the body.

Illustrations by Marta Pucci.

Cycle A-Z

Estrogen 101

Getting to know our hormones.

by Nicole Telfer, Science Content Producer; and Maegan Boutot, Former Science Writer for Clue Reviewed by Maegan Boutot, Former Science Writer for Clue
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Hormones are so much more interesting than what we’re taught in health class.  So we’ve created a guide to aaaall of the hormones. Here's everything you need to know about estrogen, progesterone, androgens, progestins, synthetic estrogen, and sex hormone binding globulin (SHBG)

What is estrogen?

Estrogen is the most famous sex hormone in women and people who menstruate. It is made from cholesterol (a type of fat molecule) within the body.

Hormones facilitate communication between cells around the entire body. Cells that have receptors for estrogen have functions which are activated or deactivated by it. Think of estrogen as a key, and estrogen receptors as a lock—together they make your body systems work.

Estrogen is not exclusive to women and people who menstruate. Men, trans-women, children, and post-menopausal women also have estrogen in their bodies. Since these people don’t have ovaries that are actively releasing eggs every month, their estrogen is made in other areas of the body, like in fat tissues, bones, skin, liver, and adrenal gland (1). In adult men, estrogen is produced in the testes (2).

What does estrogen do for the body?

You might already know that estrogen powers the menstrual cycle and the development of secondary sex characteristics (breast development, pubic hair growth) starting at puberty. But that’s not all: estrogen also plays a role in many other functions, from bone health (3) to cognitive function (4,5), and so much more.

Types of estrogen

In women and people who menstruate, there are potentially four major types of estrogen.

These types have different functions across the body over different life stages. For example, during pregnancy, different types of estrogen are produced to help support the development of the baby.

Weak estrogens can bind to estrogen receptors, but their impact on the body is not very dramatic.

  • Estrone (E1): Produced mostly in body fat, but also in the ovaries and placenta. This is a weak estrogen (6).

  • Estradiol (E2): This is the most active type of estrogen, which is the type involved in the menstrual cycle (6). This type of estrogen binds very strongly to estrogen receptors. In Clue, when we refer to “estrogen” we are almost exclusively referring to this type of estrogen.

  • Estriol (E3): This is the main estrogen of pregnancy. This type of estrogen is primarily made and secreted from the placenta (with help from the fetus) about five weeks after implantation. This is also a weak estrogen (6).

  • Estetrol (E4): This type of estrogen is only produced during pregnancy from the liver of the fetus (7).

Most of the estrogen in your body is estradiol, and is made in the ovaries. However, estrogens are also produced in other areas of the body, including fat tissues, bones, skin, liver, and adrenal glands (1). As people enter menopause, these other sources increase estrogen synthesis and become more influential in the body (8).

How does estrogen (estradiol) change during the menstrual cycle?

Remember how the menstrual cycle works? Like a relay race, many different hormones play a part in trying to fertilize and implant an egg. Estradiol is one of these main players.

Stage 1: Follicular phase = increasing estrogen

Estradiol is mostly made within the ovaries. In the first part of the cycle—the follicular phase, from the start of your period until ovulation—estradiol is produced from sacs that contain your eggs, called follicles. Estradiol stimulates the growth and thickening of the endometrium (the lining of the uterus) (6).

Near the end of the first phase, estradiol levels peak, triggering the brain to release two hormones: a large surge of luteinizing hormone (LH), and a smaller surge of follicle stimulating hormone (FSH). This then triggers ovulation. Just before ovulation, the follicle stops producing estradiol and its levels drop (6).

During the follicular phase of the cycle—from the start of your period until ovulation—estrogen levels are high. You may notice some changes throughout your body.

  • Just before ovulation, some people may notice that their skin and hair are less oily, though we don’t know for sure that the increase in estrogen causes these changes (9).

  • Your cervical fluid changes throughout the follicular phase:

  • Early-to mid follicular: dry/sticky

  • Mid-to-late follicular: thick/sticky/creamy

  • Late follicular to ovulation: wet and slippery, like an egg white (6,10)

  • Some people notice an increase in their sex drive around ovulation (11-13)

Stage 2: Luteal phase = lower estrogen

In the second part of the cycle, the luteal phase, when the follicle has ruptured and the egg has been released—ovulation has occurred. In the place where the follicle was, a new hormone producing structure forms from the walls of the follicle and is called the corpus luteum. The main function of the corpus luteum is to produce lots of progesterone, another sex hormone, but also some estradiol too (6).

If an egg is not fertilized and implanted, about four days before the start of the period, the corpus luteum stops producing progesterone and estradiol, and the levels of both hormones in the blood fall again. This triggers your period to start (6).

When estrogen is lower during the late luteal phase and the start of the period, you may notice some changes.

  • Your overall body temperature will increase slightly during this phase.

  • One study found that 2 out of 5 women report more sensitive skin, which researchers suspect could be due to low levels of estrogen during this time (14).

  • Premenstrual symptoms also show up during this time before the period starts, when estrogen (and progesterone) are low.

  • Some people may even get migraine headaches that are related to the drop in estrogen levels (15,16).

What are “normal” levels of estrogen? And what are normal levels during pregnancy? Perimenopause?

Since estrogen levels fluctuate greatly throughout the cycle, a “normal level” of estrogen changes every day (if you’re not on hormonal birth control).

But if you’re experiencing unexpected symptoms and suspect your estrogen is high or low, you might ask your healthcare provider to run tests. These levels may differ. Differences in laboratory procedures, population served by the laboratory, and testing technique can also impact results—so lab results should always be interpreted using the laboratories reference values (17).

Estrogen levels for people with regular cycles, not using hormonal birth control

Estradiol levels in the blood can range considerably across the cycle. What’s “normal” can vary based on the lab you go to, where you live, your ancestry, and the testing technique. So you should always interpret your lab results with this in mind, but you can use these reference points below.

  • Early follicular phase: 20-150 pg/mL (73-551 pmol/L)

  • Midcycle peak: 40-350 pg/mL (551-2753 pmol/L)

  • Luteal phase: 30-450 pg/mL (110-1652 pmol/L) (18)

People under 15 years old and people who are postmenopausal generally have lower levels (18).

Estrogen levels can differ dramatically from cycle to cycle, but also be very different from person to person (17,19).

Estrogen levels during pregnancy

Hormone production is really high during pregnancy. Estradiol skyrockets, along with other hormones like progesterone, testosterone, and prolactin (20). These hormones, plus many more, work together to support the development of a baby.

  • First trimester estradiol: 188–2497 pg/mL

  • Second trimester estradiol: 1278–7192 pg/mL

  • Third trimester estradiol: 3460–6137 pg/mL (20)

Perimenopause and menopause estrogen levels

After menopause, estrogen levels drop dramatically, as there are few follicles in your ovaries. Additionally, these follicles are no longer growing and producing the estradiol spikes that occur during the menstrual cycle (6). The laboratory estradiol levels of postmenopausal women are generally less than 20 pg/mL (73 pmol/L) (18).

During perimenopause, people may notice that their body changes in response to these lower levels of estrogen.

Symptoms of low estrogen during perimenopause and menopause

  • Vaginal dryness (known as atrophic vaginitis or vulvovaginal atrophy) is common. Without enough estrogen, the walls of the vagina are not able to maintain their thickness and are no longer as moist (21).

  • Hot flashes are associated with decreasing levels of estrogen, and can be treated using estrogen therapy (22). Phytoestrogens, or estrogens from food, may be moderately beneficial, but more research is needed (23).

  • Osteoporosis is a risk for post-menopausal people as estrogen levels decrease (24).

How do I know if my estrogen levels are normal?

There are many physical symptoms that can give you a clue to whether your hormone levels are within normal ranges. A lack of “normal” development during puberty, an irregular menstrual cycle, or difficulty becoming pregnant can all indicate a potential underlying hormonal problem.

Estrogen levels (along with all the other sex hormones) fluctuate and change a lot throughout the cycle and throughout life—for most people, these changes are normal and part of aging. Perimenopause in particular can be a wild hormonal ride for some people, filled with unexpected symptoms at inconvenient times (like hot flashes, insomnia, unexpected periods). Some people choose to use hormonal therapy to help control these symptoms (24).

Estrogen dominance

You may have heard about “estrogen excess” or “estrogen dominance” and how these conditions may affect the cycle. Some healthcare practitioners, bloggers, and companies have written about this topic.

Estrogen levels can be too high. For example, there is a condition that can affect estrogen levels called aromatase excess syndrome. People with this condition have higher estrogen because they convert androgens to estrogens at a much higher rate. This condition is caused by a genetic shift in the CYP19A1 gene, and the symptoms are usually present around the time of puberty (25).

It is also possible for some cancers, such as cancer of the adrenal gland, to cause high estrogen levels (26).

That being said, health bloggers are usually not talking about estrogen imbalance caused by atypical genetics or cancer. Often, these writers are discussing hormonal imbalances caused by diet, current or former use of hormonal contraception, and body fat.

In the context of online bloggers and some alternative health providers, there are different causes of “estrogen excess” or “estrogen dominance”.

  • One proposed cause is an imbalance between estrogen and progesterone. It’s thought that estrogen levels can stay too high as progesterone decreases, causing a hormonal imbalance.

  • Another proposed cause is when the estrogens E1 and/or E2 are too high in comparison to E3. Sometimes this is called an unfavorable “Estrogen Quotient”.

  • Sometimes the imbalance is thought to be caused by issues in estrogen metabolism.

Although these imbalances and issues may be real, they are often not diagnosed as a standalone condition in general medicine. Rather, some elements of the above imbalances are thought to be symptoms of another condition.

For example, high E2 and E1 levels may be a sign of polycystic ovary syndrome (PCOS) (27), which can cause irregular periods. Whether or not this estrogen ratio in PCOS is a cause or a symptom of the condition is unclear.

In contrast to mainstream medicine, some alternative healthcare providers may “diagnose” someone with these imbalances. There is little research on whether these “diagnoses” are valid as standalone conditions and not just signs of other conditions or normal fluctuations in hormones with age.

It’s also common to hear about how estrogens from the foods we eat, the products we use, and estrogens being released into the environment on our hormonal levels. Environmental exposure to endocrine disruptors, such as bisphenol-A, are recognized as having a (usually harmful) effect on the body by many medical organizations (28,29). These endocrine disruptors can interfere with hormone function.

Often bloggers will recommend changing your diet to address “estrogen excess/dominance”, usually suggesting eating diets high in (organic) vegetables and fruits, low in meat and dairy, and very little processed food (though different people have different opinions). Although eating a healthy diet is a great idea, it’s not known whether these dietary changes actually address “estrogen excess” or if people begin to feel better simply because they are eating better. Also, what is a “healthy diet” for one person may be as healthy for another person, so it’s good to listen to your body and find a diet that works for you.

If you suspect there is a problem with your hormone levels, speak to your healthcare provider about measuring the levels your sex hormone levels, including estrogen. Estrogen is usually assessed through blood testing, though estrogen tests through urine, saliva, and even amniotic fluid are also possible (18).

Be sure to track your cycle in Clue before you go, so that you can provide your healthcare provider with information about your previous cycles so that they can best interpret your lab results.

How does hormonal birth control affect estrogen?

Combined hormonal contraception (the pill, the patch, the ring) and estrogen

These types of contraception contain both estrogen and progestin, in different amounts and ratios. Many combined oral contraceptives contain ethinyl estradiol, a synthetic estrogen. In the United States, ethinyl estradiol doses do not exceed 50mcg (30), and are often lower, even 10 mcg (10). When the contraceptive pill is taken as prescribed, it works by disrupting the normal communication between the brain and the ovaries, so that:

  • hormonal fluctuations of the menstrual cycle do not happen

  • follicles are less likely to mature to their final stage, meaning less natural estrogen is produced (31)

  • ovulation does not occur (10,32)

Because follicle growth and ovulation is stopped, the natural production of estrogen (and other hormones) is affected, and may be responsible for any side effects or changes you may experience after starting the pill.  

The vaginal ring supplies a much lower dose od ethinyl estradiol of 15 mcg per day (33), and the patch supplies 20 mcg (34).

Progestin-only (IUDs, the shot, mini-pill, etc.) birth control and estrogen

There is no estrogen in progestin-only contraceptives, which include the progestin-only pill (the mini-pill), the shot, the implant, and hormonal IUDs.

Using progestin-only contraceptives may influence the fine balance and complicated interactions of some or all of the hormones involved in the menstrual cycle. Often when one hormone level is changed, a ripple occurs and others are also impacted, including estrogen. These hormonal changes may cause changes in your symptoms or menstrual cycle. Each contraceptive may impact you and your symptoms differently, and some of these changes could be the result of different estrogen levels.

The mini-pill and estrogen

Depending on the type of progestin used and the dose in the pill, ovulation is not consistently stopped (10,35). How the mini-pill impacts natural estrogen levels is not well understood, and more research is needed.

The hormonal IUD and estrogen

Hormonal IUDs are available in different progestin-doses, and usually do not stop ovulation. Whether ovulation (and thus estrogen production) stops depends on the progestin dose in the IUD and also the amount of time that IUD has been worn for (10). Ovulation is not suppressed in most cases (10,36,37).

The contraceptive injection (shot) and estrogen

The contraceptive injection works by preventing ovulation and suppressing the communication between the brain and the ovaries. Estradiol levels are much lower for people using the shot, about 15 pg/mL, though this can vary by person (38).

The implant and estrogen

The implant does not dramatically change estradiol levels (39,40). After insertion, there may be a moderate decrease in estradiol levels, but these levels slowly rose to the pre-insertion estradiol levels (or close to those levels) over two to three years (39,40).  

Non-hormonal birth control and estrogen

Non-hormonal contraceptives like condoms and the copper-IUD will not impact your natural hormonal fluctuations and estrogen levels.

To learn more about estrogen’s impacts on the cycle, check out these articles:

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