Oestrogen 101: What it is, What it Does and How it Changes-image

Oestrogen 101: What it is, What it Does and How it Changes

Medically Reviewed by Hertility on July 18, 2024

Oestrogen—the matriarch of female sex hormones. But what exactly does it do in the body, what’s its role in the menstrual cycle and what are the symptoms to look for if your oestrogen has become imbalanced? Read on to find out. 

Quick facts:

  • There are 3 different types of oestrogen, but the main one for those assigned-female-at-birth is oestradiol (E2).
  • E2 plays a big role in regulating our menstrual cycles, fertility, libido, skin health, heart health, bone density, and much more.
  • Our oestrogen levels fluctuate throughout our menstrual cycles and naturally decline with age. 
  • Imbalances in oestrogen levels are common and can be due to various underlying health conditions, medications and dietary or lifestyle factors.
  • Testing your oestrogen levels can help you figure out if you have an imbalance and see if your E2 levels could be impacting your fertility.

What is oestrogen?

Oestrogen is an important reproductive hormone in people of all sexes. It’s generally known as the ‘female’ sex hormone, because of its role in the development of the female reproductive system and regulation of the menstrual cycle

Oestrogen works to enable ovulation and produce female sex characteristics. When we have healthy levels of oestrogen, it can help us to feel feisty, frisky and fabulous.

Whilst it’s true that oestrogen plays a bigger role in those assigned-female-at-birth, everybody produces oestrogen, regardless of sex.

In those assigned-female-at-birth, oestrogen is produced mainly in ovaries and depends on other reproductive hormones including follicle stimulating hormone (FSH), luteinising hormone (LH) and testosterone for both its production and regulation.

Like all of our hormones, our oestrogen levels can sometimes become off-balanced—with many different lifestyle and genetic factors impacting its production and regulation throughout the body.

Types of oestrogen?

There are three different types of oestrogen, also sometimes spelt estrogen (the American spelling).

  • Oestrone (E1): This is mostly produced after menopause and is the least potent, often referred to as a ‘weak oestrogen’. Like all three, it is responsible for the development of female sexual development, but as it’s less potent, it sometimes serves as a repository and the body converts it to E2 when needed.
  • Oestradiol (E2): This is the most active and abundant form—and generally the one most people are talking about when they refer to oestrogen. E2 is made in the ovaries during our reproductive years (after puberty and before menopause) and plays a big role in regulating our menstrual cycle. E2 is the type we test for in our at-home Hormone and Fertility tests.
  • Oestriol (E3): Another ‘weak’ or less potent form of oestrogen that’s produced during pregnancy in the placenta. Rising during pregnancy, E3 helps to support both the uterus and embryo and maintain a healthy pregnancy throughout each term.

What does oestrogen do?

Oestrogen wears many hats—it helps to regulate our menstrual cycles, triggers the development of secondary sex characteristics like breasts and pubic hair and helps to maintain things like our skin’s moisture, our mood and even our bone and heart health.

Let’s take a look at these in more detail:

  • Helps to maintain skin moisture and elasticity: Oestrogen stimulates the production of hyaluronic acid, a substance that retains water in the skin and promotes the production of collagen and elastin, proteins that give the skin its elasticity and firmness.
  • Protects bone health: Oestrogen inhibits bone breakdown and promotes the activity of osteoblasts, special bone-building cells. Deficiency can lead to bone loss and increased risk of osteoporosis.
  • Regulates cholesterol levels and promotes heart health: Oestrogen increases the levels of high-density lipoprotein (HDL) cholesterol, often referred to as “good” cholesterol, which helps remove low-density lipoprotein (LDL) cholesterol, or “bad” cholesterol, from the bloodstream, reducing the risk of plaque buildup in the arteries. It also helps to promote the dilation of blood vessels, which can improve blood flow to the heart.
  • Regulates mood: Oestrogen influences neurotransmitters, such as serotonin and dopamine, which are involved in mood regulation. Fluctuations in oestrogen levels during the menstrual cycle or menopause can affect neurotransmitter activity and lead to changes in mood.
  • Regulates the menstrual cycle: Oestrogen plays a central role in regulating the menstrual cycle and ovulation (more on that below).
  • Stimulates the development of female secondary sex characteristics: Oestrogen is responsible for breast development, the widening of hips, the deposition of fat in certain areas of the body and the enhancement of pubic and underarm hair growth during puberty.
  • Helps to grow the lining of the womb, vagina and vulva: Oestrogen promotes the growth and maintenance of the uterine lining (endometrium) during the menstrual cycle. It also helps maintain the thickness and health of the vaginal and vulvar tissues, keeping them lubricated and preventing dryness.
  • Helps to grow the lining of the womb, vagina and vulva: Oestrogen promotes the growth and maintenance of the uterine lining (endometrium) during the menstrual cycle. It also helps maintain the thickness and health of the vaginal and vulvar tissues, keeping them lubricated and preventing dryness.

What is oestrogen’s role in the menstrual cycle?

Like all of our menstrual cycle hormones, our oestrogen levels during the menstrual cycle fluctuate. 

During the first part of our menstrual cycles, the follicular phase, which lasts from day 1 of our periods until ovulation (when we release a mature egg), our oestrogen levels start off low but steadily increase. In this phase, our eggs are maturing in preparation for ovulation. 

Our eggs mature in our ovaries, in little sacs called follicles. These follicles make oestrogen, so whilst your eggs are maturing, your follicles steadily release this oestrogen—and it rises until it reaches a peak, just before we ovulate.

Because of oestrogen’s feel-good factors, just before and during ovulation is the time of the month when we’ll be killing it, feeling our most fierce and fabulous. This is the time to book that big presentation at work, go on that first date or really push it in your gym session.

This peak in oestrogen causes a surge in LH, which triggers the release of a mature egg from one of our ovaries during ovulation.

After ovulation, oestrogen levels gradually drop and despite a small second wind around a week later, they continue to level off throughout the second stage of our menstrual cycles—the luteal phase.

At the end of our cycles, if the ovulated egg has not met a sperm and been fertilised, all of our menstrual cycle hormones, including oestrogen, drop off to their baseline levels—triggering our periods. 
If our oestrogen levels get off balance, it can disrupt the balance of our other menstrual cycle hormones—potentially impacting ovulation.

No ovulation = no pregnancy. So if you’re trying to get pregnant, testing your hormone levels is really important for understanding your ovulation and general menstrual cycle health.

What affects oestrogen levels?

As well as fluctuating naturally month to month, lots of other lifestyle, genetic and medical conditions can affect our oestrogen levels, including:

  • pregnancy, postnatal hormonal fluctuations, and breastfeeding
  • puberty and menopause
  • being overweight and obesity
  • extreme dieting or anorexia nervosa
  • strenuous exercise or overtraining
  • the use of certain medications, including steroids, ampicillin, oestrogen-containing drugs, phenothiazines, and tetracyclines
  • some congenital conditions, such as Turner’s syndrome
  • high blood pressure
  • diabetes
  • primary ovarian insufficiency (POI)
  • an underactive pituitary gland
  • polycystic ovary syndrome (PCOS)
  • tumours of the ovaries or adrenal glands

Does oestrogen decline with age?

Thanks to our wonderful ‘biological clocks’, as we age, our oestrogen levels gradually decline. This is because our number of egg cells decreases as we age and as a result, our follicles stop growing and producing as much oestradiol (E2).

After menopause (when our periods stop completely), our E2 levels completely drop off, which is what causes the common low oestrogen menopausal symptoms like hot flushes, dry skin and mood swings. During perimenopause (the lead up to menopause), E2 levels fluctuate up and down which can also cause menopausal symptoms.

Declining oestrogen levels has whole-body knock-on effects, but luckily these days hormone replacement therapy (HRT) can be a great option to relieve symptoms for many people during perimenopause and postmenopause.

How do I know if my oestrogen levels are normal?

Because our oestrogen levels fluctuate during our cycles, as we age, and are dependent on whether we’re taking hormonal birth control or not, our ‘normal’ level is constantly changing. 

Like all of our hormones, our oestrogen is super sensitive and can easily get off balance. Oestrogen imbalances can cause a whole host of symptoms and can be caused by both lifestyle and genetic factors.

Symptoms of high oestrogen levels

Oestrogen dominance is a phrase that has been used to describe a phenomenon when oestrogen levels are too high in relation to the other sex hormones in your body. 

Although it’s not a clinically recognised term, being more sensitive or having excess oestrogen is known to cause symptoms like irregular periods, abnormal vaginal bleeding, bloating, swollen or tender breasts and weight gain.

Some causes of high oestrogen levels include underlying health conditions, genetic factors, dietary and lifestyle factors and environmental pollutants.

Symptoms of low oestrogen levels

On the flip side, when oestrogen levels are too low we can experience irregular periods, fertility difficulties, reduced bone density, vaginal dryness, hot flashes and dry skin—to name a few. 
Having very low oestrogen levels can be caused by your ovaries not working properly, which occurs in menopause or primary ovarian insufficiency (POI). However, underlying health conditions like pituitary gland disorders, as well as having very low levels of body fat, a high caffeine intake, smoking and excessive exercise can also result in lower oestrogen levels.

Luckily, testing our E2 levels with a hormone test can help us to decipher if our oestrogen levels are within the normal range for us.

Oestrogen FAQs

Where can I get an oestrogen blood test?

You’ve landed in the right place. With a Hertility Hormone and Fertility test you can get an accurate reading of your baseline E2 levels alongside other reproductive hormones. Your test will be sent straight to your door for you to do at-home and you’ll receive a doctor-written report along with your results. If your E2 levels come back out of range, you can arrange to chat with one of our doctors and we can support you with whatever treatments you may need.

Can I get pregnant with high oestrogen levels?

Technically, yes. Although it can be harder as high oestrogen (which some people refer to as oestrogen dominance) can impact your fertility because of how it throws off your other menstrual cycle hormones. If you’re experiencing symptoms of oestrogen dominance it’s best to get your hormones tested before you try to conceive so you know where you’re at.  

How can I increase oestrogen levels?

Firstly, the cause of low oestrogen levels must be identified. If you have not gone through menopause, have no underlying conditions and lead a healthy lifestyle but are struggling with low oestradiol symptoms, your doctor might suggest going on hormonal contraception to improve them.

Certain lifestyle factors like smoking, being underweight or exercising excessively can also cause lower levels of oestrogen.  If you’re going through perimenopause or gone through menopause, hormone replacement therapy (HRT) is an effective way to improve symptoms of low oestrogen. HRT comes in the forms of topical gels, sprays, patches, pessaries and oral tablets. 

How can I reduce oestrogen levels?

Again, there are several lifestyle factors you can try to reduce your oestrogen levels if you have oestrogen dominance. These can include, reducing your alcohol intake (alcohol spikes our oestrogen levels), reducing caffeine intake, focusing on an oestrogen-friendly diet in general such as eating more fibre, improving your sleep and losing any excess body fat.

Again, your doctor may suggest trying some hormonal contraception to regulate your oestrogen levels if they are high.

Are there natural oestrogen supplements?

If you’re looking to naturally boost oestrogen levels, have a look to see if there are any changes you can make to your lifestyle. Consuming a healthy, balanced diet (focusing on a Mediterranean diet can help), as well as cutting down on stress, smoking and excessive exercise are all things you could do to ensure your oestrogen levels are in check.


Ruby Relton

Ruby Relton

Ruby is a scientific researcher specialising in reproductive science and women’s health, with a BSc in Biomedical Science from the University of Strathclyde and an MSc in Reproductive Science and Women’s Health from UCL—where she received the Anne McLaren Award for academic excellence, featuring on the Dean's list of outstanding students. Ruby's research includes inequalities and diversity in reproductive health, menopause and sports gynaecology.

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