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What is Estriol?

Since Estriol is the active ingredient in our Natural Estrogen Cream people often ask us “What is Estriol and what does it do?”.   Estriol, aka E3, is one of the three major endogenous estrogens occurring naturally in the female human body. The other two hormones belonging to the group are estradiol (E1) and estrone (E2). Of these 3 estrogens, estriol is a steroid which functions as a minor female hormone, usually secreted during pregnancy. The level of the hormone in non-pregnant women is almost undetectable.

At first, estriol was regarded with little or no significance due to its relatively low activity compared with the other members of the estrogen family. This relative inactivity led several people to reach a conclusion that estriols are too weak to matter in the human body. While estriol may be synthesized in little quantities or may be too weak to matter, ongoing research suggested that it can safely perform the same function as the other members of the estrogen family thus reducing symptoms associated with perimenopause and menopause.

Estriol is mainly synthesized in high quantities by the placenta. It is one of the less produced estrogens in the body and it circulates in similar ways as the other members of the estrogens due to a relatively high rate of metabolism and excretion.

Functions of Estriol

All members of the estrogen group function to bring about secondary sexual changes in the female body such as the enlargement of the breast and hips, but doesn’t stop there. The other functions common with Estriol are:

  • Reduction in the prevalence of perimenopausal and menopause symptoms such as hot flashes, vaginal dryness, and loss of bone density.
  • Prevents post-menopausal urinary tract infections.
  • Protects the bones against the occurrence of osteoporosis.

While a lot of people are of the view that estriol is the weakest of all estrogens, it will interest you to know that Estriol’s strength is found in its weakness. Tests carried out on these hormones reveal that using estrogens to control perimenopausal and menopausal symptoms are linked with some complications and side effects such as breast cancer; BUT it’s actually the weak activity of estriol makes it one of the best treatments for the perimenopausal and menopausal symptoms because it doesn’t lead to the complications that have been associated with estradiol and estrone.

This weak activity allows it to bind to estrogen receptors on the breast cells but with a weaker activity. The presence of estriol blocks the activity of estradiol from binding to the cells and this subjects them to a higher estrogenic activity which protects against breast cancer.

Therefore, Estriol may be the best option for women who have a high sensitivity or reactivity to the stronger estrogens for the treatment of hormonal imbalance due to aging.

Side effects of Estriol

Contrary to what is obtainable from the other members of the estrogen group, the use of estriol in the treatment of perimenopausal and menopausal symptoms has little or no side effects since it has a weak activity and binds to a different estrogen receptor which limits the activity of the other members of the estrogen group.


While research has shown that the use of estriol is safer for women who cannot tolerate higher levels of estrogen, we suggest you consult with your physician before engaging in any form of HR.

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