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

Oestrogen is a group of hormones that controls your menstrual cycle and supports your fertility, bones, heart, skin, mood and vaginal health. The main type before menopause is oestradiol. Your oestrogen levels rise and fall across your cycle and gradually fall with age, and levels that are too high or too low can cause symptoms.

You might have come across oestrogen because your periods have changed, you’re trying to conceive, or you’ve noticed symptoms that could be hormonal. This guide explains what oestrogen does, how it changes through your cycle and life, the signs of high and low oestrogen, and how to get your levels tested.

Quick facts:

• There are three main types of oestrogen. Oestradiol (E2) is the most active type during your reproductive years.
• Oestrogen helps control your menstrual cycle, ovulation and fertility. It also supports your libido, skin, heart, bones and mood.
• Your oestrogen levels change throughout your cycle and naturally fall with age, so there’s no single “normal” level.
• Oestrogen levels can be affected by health conditions, medicines, your weight, diet and lifestyle.
• Low oestrogen can cause irregular or missed periods, hot flushes, vaginal dryness and weaker bones.
• “Oestrogen” and “estrogen” are the same hormone. Estrogen is the American spelling.

Not sure whether your oestrogen is behind your symptoms? Hertility’s Advanced Hormone and Fertility Test checks your oestradiol alongside other key hormones from home, timed to your cycle. You’ll get a doctor-written report explaining what your results mean for you.

What is oestrogen?

Oestrogen is a reproductive hormone that everyone makes, whatever their sex. Levels are much higher in women. It’s often called the “female” sex hormone because it drives the development of the female reproductive system and controls the menstrual cycle.

Before menopause, most oestrogen is made in your ovaries by follicles, the small sacs that contain your developing eggs. Its production depends on other hormones:

• follicle stimulating hormone (FSH) and luteinising hormone (LH), which are made by your brain and tell your ovaries to make oestrogen
• testosterone , which your ovaries convert into oestrogen

Smaller amounts of oestrogen are also made in fat tissue.

What are the different types of oestrogen?

Your body naturally makes three main types of oestrogen, plus a fourth specialised type found during pregnancy:

• Oestrone (E1) It becomes the main type after menopause, when it’s mostly made in fat tissue. Your body can convert it into oestradiol when it’s needed. This is a weak form of oestrogen.
• Oestradiol (E2) is the most active and abundant type, and usually the one people mean when they talk about oestrogen. Your ovaries make it between puberty and menopause, and it plays a big role in controlling your cycle. It’s the type measured in Hertility’s Advanced Hormone and Fertility Test.
• Oestriol (E3)  It’s made by the placenta during pregnancy, where it helps support the womb and the developing baby. This is also a weak form of oestrogen.
• Estetrol (E4): A type of oestrogen that is only produced during pregnancy by the liver of the developing baby.

Weak forms of oestrogens can attach to oestrogen receptors, but their effect on the body is less compared to more active oestrogens. 

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:

• It controls your cycle and ovulation. Rising oestrogen helps trigger the release of an egg each month.
• It builds your womb lining. It thickens the lining of your womb (the endometrium) each cycle, ready for a fertilised egg to implant.
• It keeps your vagina and vulva healthy. It keeps these tissues thick, moist and elastic, which helps prevent dryness.
• It drives the changes of puberty. These include breast development, wider hips, changes to where your body stores fat, and the growth of pubic and underarm hair.
• It keeps your skin healthy. It helps your skin hold moisture by boosting hyaluronic acid, a substance that holds water in the skin. It also supports collagen and elastin, the proteins that keep your skin firm.
• It protects your bones. It slows bone breakdown and supports the cells that build new bone. When oestrogen falls, bone density can drop, raising the risk of osteoporosis.
• It supports your heart and blood vessels. It tends to raise HDL (“good”) cholesterol, which helps clear LDL (“bad”) cholesterol. It also helps your blood vessels relax and widen. This is one reason heart disease risk rises after menopause.
• It affects your mood and brain. It influences brain chemicals involved in mood, such as serotonin and dopamine. That’s why changing levels before a period or during perimenopause can affect your mood, sleep and concentration.
• It supports your sex drive. Healthy oestrogen levels support your libido and keep sex comfortable.

How does oestrogen change during your menstrual cycle?

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

1. At the start of your period, oestrogen is low.

2. In the first half of your cycle (the follicular phase), eggs mature inside follicles in your ovaries. As the follicles grow, they release more oestrogen, so levels rise steadily.

3. Just before ovulation, oestrogen peaks. This triggers a surge of LH, which causes a follicle to release a mature egg. 

During this phase of your cycle i.e. from the start of your period to ovulation, oestrogen levels are high. You may notice your skin is feeling clearer and you have increasing energy levels and improved mood. Your cervical fluid also changes throughout the follicular phase, during the early to mid follicular it is dry or sticky, around the mid to late follicular phase it can become thicker, sticky or creamy and as you move towards ovulation, it becomes wet and slippery, like egg white. Additionally, some people notice an increase in their libido around ovulation.

4. In the second half of your cycle (the luteal phase). After the egg is released, the follicle’s walls form a new structure called the corpus luteum. The main function of the corpus luteum is to produce high levels of progesterone and some oestrogen. Progesterone rises to prepare your womb lining for a possible pregnancy.

5. If the egg isn’t fertilised, oestrogen and progesterone fall back to baseline, and this triggers your period. When oestrogen levels are lower before your period, you may start noticing Premenstrual symptoms (PMS).

Why this matters for getting pregnant. Oestrogen helps trigger ovulation, so low or disrupted oestrogen can affect whether you ovulate. If you don’t ovulate, you can’t get pregnant. That’s why checking your hormones is useful if you’re trying to conceive. Read more about ovulation.

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
• extreme dieting or anorexia nervosa
• strenuous exercise or overtraining without refuelling adequately
• 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

How does oestrogen affect your fertility?

Oestrogen is involved in almost every step of getting pregnant.

It triggers ovulation. As follicles grow in the first half of your cycle, they release more and more oestrogen. When levels peak, they trigger the surge of LH that releases an egg.

It helps sperm reach the egg. Rising oestrogen changes your cervical mucus, making it clear, slippery and stretchy around ovulation. This type of mucus helps sperm swim through your cervix towards the egg.

It prepares your womb. Oestrogen thickens your womb lining so that a fertilised egg has somewhere to implant. Progesterone then takes over after ovulation to keep the lining ready.

If your oestrogen is low, you may not ovulate regularly, and your womb lining may stay thin. If your oestrogen is high compared with progesterone, it’s often a sign that you’re not ovulating every cycle. Either way, it can make it harder to conceive.

That’s why oestradiol is one of the hormones usually checked when you’re trying to get pregnant. It’s also closely monitored during IVF and egg freezing, to track how your follicles are growing. If you’re trying to conceive and your cycles are irregular, Hertility’s Advanced Hormone and Fertility Test can help you understand what’s going on.

Does oestrogen decline with age?

Yes. As you get older, your ovaries contain fewer eggs and follicles, so they gradually make less oestradiol.

During perimenopause, the years leading up to menopause, oestrogen doesn’t fall steadily. It goes up and down unpredictably, which can cause irregular periods, hot flushes and mood changes. Read our guide to what perimenopause is.

After menopause, once you’ve gone 12 months without a period, oestradiol falls to low levels and oestrone becomes the main type. Lower oestrogen causes many common menopause symptoms, such as hot flushes, vaginal dryness, dry skin and mood changes. It also raises your long-term risk of osteoporosis and heart disease.

Hormone replacement therapy (HRT) can relieve symptoms of low oestrogen for many people during perimenopause and after menopause. Find out more about menopause stages, symptoms and treatments.

Does hormonal contraception affect oestrogen?

Yes, but in different ways depending on the type.

The combined pill, patch and vaginal ring contain a synthetic form of oestrogen, along with a progestogen. They stop you ovulating, so your ovaries make much less of their own oestradiol. The oestrogen in your contraception takes its place, which is why you’re unlikely to have symptoms of low oestrogen while using them.

Progestogen-only methods, such as the mini pill, implant and injection, don’t contain oestrogen. The progestin has several effects in the body that help prevent pregnancy, the mucus in the cervix thickens, making it difficult for sperm to enter the uterus and fertilize an egg. Some of these methods stop ovulation and also thin the lining of the uterus. However, your own oestradiol usually is not drastically affected while on the mini-pill and implant. The contraceptive injection, however, can impact oestrogen levels.

The hormonal coil are available in different progestin doses and usually do not stop ovulation. Whether ovulation (and thus oestrogen production) stops depends on the progestin dose in the IUD and how long the IUD has been in place. Ovulation is not stopped in most cases.

The copper coil contains no hormones, so it doesn’t affect your oestrogen.

Hormonal contraception can affect your test results, so always tell your doctor or testing provider what you’re using. Read more abouttesting your hormones on hormonal contraception.

How do I know if my oestrogen levels are normal?

There’s no single normal oestrogen level. Oestradiol changes so much that a result only makes sense alongside a few other things.

The day of your cycle. In a natural cycle:

• Oestradiol is lowest at the start of your period.
• It rises steadily to a peak just before ovulation, often several times higher than your starting level.
• It falls after ovulation, then rises a little again in the second half of your cycle.

A result that’s normal just before ovulation would look high at the start of your cycle.

Your life stage.

• Oestradiol is much higher in pregnancy.
• It goes up and down unpredictably in perimenopause.
• It’s low after menopause.

Your contraception. Hormonal contraception can suppress your natural oestradiol, so your result needs to be read with that in mind.

The lab. Oestradiol is usually measured in picomoles per litre (pmol/L) in the UK. But different labs use different methods and reference ranges, so a result should always be compared with the range given by the lab that ran it.

That’s why oestradiol is usually tested around day 3 of your cycle, when it’s at its baseline, and alongside FSH and LH. A raised FSH with a low oestradiol, for example, can suggest your ovaries are working harder to respond. Find out why cycle day 3 matters for hormone testing.

What happens when oestrogen is too high?

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.

High oestrogen is often less about the amount of oestrogen itself, and more about the balance between oestrogen and progesterone. When oestrogen isn’t balanced by enough progesterone, you may notice:

• heavier or irregular periods, or bleeding between periods
• breast tenderness or swelling
• bloating
• worse PMS and mood changes
• weight gain

Higher oestrogen usually happens for one of three reasons.

You’re not ovulating regularly. Progesterone is mainly made after ovulation. So if you don’t ovulate every cycle, oestrogen can go unbalanced. This is common with PMOS (formerly known as PCOS) and during perimenopause, when oestrogen can also spike higher than usual. Over time, unbalanced oestrogen can thicken your womb lining too much. That’s one reason long gaps between periods should be checked.

Your body is making more oestrogen. Oestrogen rises naturally in pregnancy. Carrying extra weight can also raise oestrogen, because fat tissue makes it. Rarely, a tumour of the ovary or adrenal gland can produce extra hormones.

Medicines. Some hormonal medicines can raise oestrogen levels.

Some research suggests that certain chemicals in the environment, known as endocrine disruptors, may also affect hormone levels, but the evidence is still developing.

What is “oestrogen dominance”?

You’ll often see “oestrogen dominance” online, usually alongside supplements or diets that claim to fix it. It describes oestrogen being high compared with progesterone, but it isn’t a recognised medical diagnosis. The symptoms people link to it can have many different causes, so it’s better to find out what’s actually going on with a doctor than to try to “balance” your oestrogen yourself.

What happens when oestrogen is too low?

When oestrogen is too low, the effects show up across your body. Your periods may become irregular, light or stop altogether, and you may not ovulate, which can make it harder to get pregnant. Without enough oestrogen, the tissues of your vagina can become dry and thin, which can make sex uncomfortable. You may also notice:

• hot flushes and night sweats
• a libido
• poor sleep
• low mood
• dry skin

Over time, low oestrogen can weaken your bones.

Low oestrogen usually happens for one of two reasons.

Your ovaries are making less oestrogen. This is what happens naturally during perimenopause and menopause, as your egg supply runs low. It can also happen earlier with premature ovarian insufficiency (POI), where your ovaries stop working normally before the age of 40. Treatments such as chemotherapy, radiotherapy or surgery to remove the ovaries can also stop the ovaries producing oestrogen.

Your brain isn’t sending the usual signals to your ovaries. Your ovaries need signals from your brain to make oestrogen. If your body doesn’t have enough energy, it can switch these signals off to save energy. That can happen if you have very low body weight, an eating disorder, eat too little for the amount of exercise you do, or are under severe stress. This is known as hypothalamic amenorrhoea. Problems with the pituitary gland, which sends these signals, can have the same effect.

Other factors. Smoking is linked with lower oestrogen and an earlier menopause. Oestrogen is also naturally low while you’re breastfeeding.

If your periods have stopped, or you’re under 40 and have symptoms of low oestrogen, speak to your GP. Low oestrogen affects your long-term health, so it shouldn’t be ignored.

How do I test my oestrogen levels in the UK?

Oestrogen is measured with a blood test. In the UK, you can get it tested through the NHS, at a private clinic or with an at-home test.

On the NHS. Your GP may test your oestradiol if your periods are irregular or have stopped, you’re having difficulty getting pregnant, or you have symptoms that suggest a hormone problem. It’s usually tested alongside FSH and LH. If you’re 45 or over and have typical symptoms of perimenopause, you usually won’t need a blood test, because perimenopause can be diagnosed from your symptoms. But testing can still help rule out other causes.

At a private clinic. Private GP services and clinics can test your oestradiol without a referral, usually from a blood sample taken from your arm.

At home. Hertility’s Advanced Hormone and Fertility Test lets you test your oestradiol from home with a finger-prick sample, or you can book a nurse visit. It starts with an Online Health Assessment that builds a personalised panel of up to 10 hormones. Your test is timed to your cycle, and your results come with a doctor-written report and a personalised Care Plan. If your oestradiol is outside the expected range, you can speak to a Hertility expert about what it means and what to do next.

Can you change your oestrogen levels?

Sometimes. It depends on why your levels are high or low, so the first step is always finding the cause.

If your oestrogen is low:

• If it’s caused by under-eating, very low body weight or intense exercise, restoring your energy balance by eating enough and reducing very intense training can help your cycle return. This can take time, so get support from a doctor or dietitian, especially if your periods have stopped.
• If you smoke, stopping is one of the most helpful things you can do.
• If it’s caused by perimenopause, menopause or POI, hormone replacement therapy (HRT) is the most effective treatment. It comes as tablets, patches, gels, sprays and vaginal pessaries. For some people with low oestrogen, the combined contraceptive pill may be an option instead.

If your oestrogen is high, treatment depends on what’s causing it:

• If you’re not ovulating regularly, for example because of PMOS, treating that condition can help bring your hormones back into balance.
• Lifestyle changes may help. Keeping to a healthy weight and cutting down on alcohol, which is linked with higher oestrogen levels, may both help. A high-fibre diet and good sleep support your overall hormone health.
• Your doctor may suggest hormonal contraception to regulate your cycle.

What about natural oestrogen supplements? Plant compounds called phytoestrogens, found in soy and in supplements such as red clover, are sometimes promoted as a natural way to boost oestrogen.NICE guidance notes they may help some menopause symptoms, but the quality of supplements varies and their safety isn’t fully known. Speak to your doctor before taking any supplement, particularly if you have a history of breast cancer.

When should you see a doctor about your oestrogen levels?

Speak to your GP if:

• your periods have stopped for three months or more and you’re not pregnant
• you’re under 40 and your periods have become irregular or stopped
• you have symptoms of low oestrogen, such as hot flushes or vaginal dryness, and you’re under 45
• you’ve been trying to get pregnant and your periods are irregular
• your symptoms are affecting your daily life

See your GP promptly if you have:

• very heavy periods
• bleeding between periods or after sex
• any bleeding after you’ve gone 12 months without a period

These need checking to rule out other causes.

Get answers about your hormones with Hertility

If you think your oestrogen might be affecting your periods, fertility or wellbeing, Hertility can help you find out what’s going on:

• Hertility’s Advanced Hormone and Fertility Test checks your oestradiol alongside other key hormones, with a doctor-written report and a personalised Care Plan.
• A Menopause Consultation can help if you think you’re in perimenopause or menopause, including talking through HRT.
• A Nutrition Consultation can help if diet, weight or exercise could be affecting your hormones.

Not sure where to start? Take the Online Health Assessment and we’ll build a personalised plan around your symptoms and goals.

Oestrogen FAQs

Where can I get an oestrogen blood test?

With a Hertility Advanced 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.

What are the symptoms of low oestrogen?

Symptoms of low oestrogen include irregular or missed periods, hot flushes, night sweats, vaginal dryness, a lower sex drive, mood changes and difficulty getting pregnant. Over time, low oestrogen can also weaken your bones. Common causes include perimenopause, menopause, very low body weight and intense exercise.

What are the symptoms of high oestrogen?

High oestrogen, particularly compared with progesterone, may be linked with heavy or irregular periods, breast tenderness, bloating, weight gain and worse PMS. Possible causes include pregnancy, carrying extra weight, some medicines, perimenopause and, rarely, hormone-producing tumours.

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. 

What does oestrogen do in the body?

Oestrogen controls your menstrual cycle and ovulation, and builds your womb lining each month. It also keeps your vaginal tissues healthy, protects your bones, supports your heart and blood vessels, and affects your skin, mood, sleep and sex drive.

Is oestrogen the same as estrogen?

Yes. “Oestrogen” is the UK spelling and “estrogen” is the American spelling. They’re the same hormone.

Resources:

• Society for Endocrinology. You and Your Hormones: Oestradiol. https://www.yourhormones.info/hormones/oestradiol/
• Society for Endocrinology. You and Your Hormones: Oestrone. https://www.yourhormones.info/hormones/oestrone/
• Society for Endocrinology. You and Your Hormones: Oestriol. https://www.yourhormones.info/hormones/oestriol/
• NHS. Osteoporosis. https://www.nhs.uk/conditions/osteoporosis/
• NHS. Hormone replacement therapy (HRT). https://www.nhs.uk/medicines/hormone-replacement-therapy-hrt/
• NHS. Early menopause. https://www.nhs.uk/conditions/early-menopause/
• National Institute for Health and Care Excellence (NICE). Menopause: identification and management (NG23). https://www.nice.org.uk/guidance/ng23
• Delgado BJ, Lopez-Ojeda W. Estrogen. [Updated 2021 Apr 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538260/
• Reed BG, Carr BR. The Normal Menstrual Cycle and the Control of Ovulation. [Updated 2018 Aug 5]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279054/