The primary female sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics.

Oestrogen is one of the most important, and most well-known, female sex hormones. Alongside the hormone progesterone, oestrogen is needed for female bodies to be able to function and undergo:

  • Puberty (including the development of secondary sex characteristics, such as breasts)
  • The menstrual cycle
  • Pregnancy

The hormone may primarily be known around the world for its function in female sexual and reproductive health, but this is not where its uses end. It also plays various roles and offers various functions around the body, contributing to:

  • Cognitive health
  • Bone health
  • Maintaining healthy cholesterol
  • Maintaining healthy skin
  • The functioning of the cardiovascular system
  • Other essential bodily functions in both male and female bodies

Both male and female bodies produce oestrogen, but female bodies will normally produce more of it. In a female body, oestrogen will primarily be produced by the ovaries, but some will also be produced by the adrenal glands and fat tissues. In a male body, oestrogen will be produced in the testes, as well as the adrenal glands. Altogether, these parts help to make up the human endocrine system, which helps the oestrogen to move through a person’s bloodstream.

Different types of oestrogen may be produced at different times and under different circumstances. For convenience, these have been noted separately below.

Oestrone (E1)

This type of oestrogen is present in the female body after menopause. It is a steroid, a minor sex hormone, and a weaker form of oestrogen that can be converted into other forms of oestrogen by the body if this should ever be necessary.

Oestradiol (E2)

This type of oestrogen is an oestrogen steroid hormone and the major female sex hormone. This makes it the most common type of oestrogen in female bodies during the person’s reproductive years. Despite this, oestradiol is produced in both male and female bodies.

Oestradiol is involved in the regulation of the menstrual cycle and is the type of oestrogen that is responsible for secondary sexual characteristics in females. These include the development of breasts, the widening of the hips, and the female-associated pattern of fat distribution. It is also important in the development and maintenance of female reproductive tissues, such as mammary glands, the uterus, and the vagina during puberty, adulthood, and pregnancy.

As well as assisting the female reproductive system, oestradiol also contributes to the healthy functioning of bone tissue, fat, the skin, the liver, and the brain.

Oestriol (E3)

This type of oestrogen is a steroid and a minor sex hormone, as well as being a weak type of the hormone. Levels of oestriol in women, non-binary, or transgender people who are not pregnant are almost undetectable. However, these levels rise during pregnancy because oestriol is synthesised in large quantities by the placenta. Doing this allows the uterus to grow, preparing the body for the baby to be delivered.

Levels of this hormone will peak just before the person gives birth.

Oestetrol (E4)

This is a weak oestrogen steroid hormone only ever produced in detectable levels during pregnancy. It is produced exclusively by the foetal liver.