Diagram of the molecular structure of estrogen.
Scientifically Reviewed
Home/Cycle Matters / Reproductive Health

Hormones 101: What is estrogen?

Our bodies are complicated, but learning about them doesn’t have to be. Discover the role of hormones in the menstrual cycle, as we answer questions like ‘what is estrogen?’, ‘what is estrogen dominance?’ and more. But first, let’s start at the beginning and kick off with the basics.

What is a hormone?

In simple terms, a hormone is a chemical substance that acts as a signal to different parts of the body. Hormones are produced in glands and then travel through the body to other tissues where they give a message, which in turn triggers a process. Hormones are produced by various glands throughout the body and are part of a fine balance that keeps the body functioning normally.

What is estrogen?

Estrogen or oestrogen is the main female sex hormone. Estrogen is not exclusive to female reproductive health. It also plays an important role in men’s bodies too – just as testosterone (typically associated with masculinity), has a function in the female body.  However, estrogen is found in higher quantities in women, as we’ll discover from its role in the menstrual cycle.

As well as being a crucial part of a healthy menstrual cycle, you may also recognize estrogen, as it’s common in hormonal birth control, as well as in HRT (hormone-replacement therapy). Birth control methods containing synthetic estrogens work by keeping hormone levels consistent and so preventing ovulation.

Estrogen and the menstrual cycle

In women, estrogen is primarily produced in the ovaries. Throughout the menstrual cycle, estrogen levels vary depending on the stage of the cycle. This sex hormone controls the growth of the lining of the uterus in the first stage of the cycle (known as the follicular phase). After ovulation, if the female egg cell is not fertilized, then a woman’s estrogen levels decline sharply, this triggers her period and the start of a new menstrual cycle. Estrogen also has an important link with another key sex hormone, progesterone.

What is estrogen dominance?

Our bodies are fine-tuned and complex, so it sometimes happens that hormones become imbalanced. One way this can happen is through estrogen dominance, which in turn relates to other health issues. Estrogen dominance can present with the following symptoms:

  • Breast tenderness and swelling
  • Fibrocystic breast lumps
  • A slump in libido (sex drive)
  • Irregular menstrual cycle (as well as heavy periods or no periods)
  • Increased premenstrual syndrome
  • Mood swings
  • Anxiety
  • Headaches
  • Weight gain
  • Hair loss
  • Cold hands and feet
  • Lethargy
  • Trouble sleeping
  • Memory problems

These can also be symptomatic of other conditions as every woman’s cycle is unique. This should not be used as a diagnosis and you should speak to your healthcare professional if you have any concerns or think you might be affected by estrogen dominance.

Birth control without hormones

Natural Cycles is a birth control app that is powered by an algorithm that tracks your body temperature. This data can tell you where you are in your cycle, so you know your own fertility. If you’re looking for a non-hormonal method that will teach you more about your body, Natural Cycles might be a suitable birth control option for you.

Did you enjoy reading this article?

Discover Natural Cycles° today

Jen on the roof terrace at Natural Cycles headquarters.

Written By

Jennifer Gray

Jennifer Gray is an award-winning writer with more than five years’ experience covering reproductive topics ranging from birth control to planning pregnancy. She is passionate about providing women with accurate information grounded in science they can use to take charge of their own health - while also dispelling myths that exist within the field of women’s health. She holds a Master of Science from the University of Edinburgh and currently lives in Ireland.

Jack in a suit and tie holding a microphone and giving a presentation.

Scientifically Reviewed

Jack Pearson

Dr. Jack Pearson is a previously HCPC registered Embryologist with a PhD in reproductive medicine. Prior to joining Natural Cycles leading Medical Affairs, he worked for more than 10 years in a clinical setting working at some of the busiest fertility clinics in the UK. Today he spends most of his time working with experts at the world’s leading institutions to carry out important research with the vision to further the field of female health. He earned his PhD from the University of Sheffield specializing in Sperm Metabolism and currently lives in London.

Featured Posts

Birth Control

11 Non-hormonal birth control methods and how they work

13 min read

Birth Control

Switching birth control methods: what you need to know

9 min read

Period & Bleeding

11 Signs your period is coming

11 min read

Want to learn more about a hormone-free future?

Subscribe to our newsletter for access to our latest articles, exclusive promotions and more.

Keep reading...

Reproductive Health

How long do sperm live?

Sperm can live inside a woman's body for up to five days. If you have unprotected sex even a few days before you ovulate, there's a chance of getting pregnant. In this article, we’re tackling the life cycle of sperm, plus their survival rate in different circumstances. Read on to learn more about what can influence sperm production, survival, and health.

6 min read

Reproductive Health

Basal body temperature & natural family planning

The basal body temperature (BBT) method – a.k.a the temperature method – is a type of natural family planning that tracks your body’s temperature to help determine when you are ovulating. In this article, we will cover the crucial link between measuring basal body temperature and finding your fertile window. We’ll also look at what to expect when using the temperature method and how the BBT method can be used to help you plan or prevent pregnancy.

7 min read

Reproductive Health

Why is my menstrual cycle getting shorter?

We can experience a shorter menstrual cycle for many reasons, like recent use of birth control, pregnancy, perimenopause, and more. Tracking your cycle can help you notice if and when your cycle is getting shorter. Cycle regularity can be a useful indicator of our overall health, so it’s good to be aware of what may cause things to change. In this article, we’ll explore some of the reasons for a shorter menstrual cycle, the causes for an irregular period, and when to reach out to a healthcare provider.

6 min read