There are three main forms of estrogen in the body:
1) Estrone E1
2) Estradiol E2
3) Estriol E3
Some of the differences are estrone, E1 for short, is the one estrogen that remains in the body even after menopause and is often the one thought to be responsible for the female related cancers such as breast cancer, because it unopposed by other hormones to help provide the healthy balance, that is meant to be.
EstradioI is nicknamed E2 and that is the predominant hormone that we use to help abate some of those symptoms such as hot flashes, night sweats, mood swings, etc.
Estriol, E3 is called the third or sometimes even called a weak estrogen because it actually helps balance the estrogen activity in the body by almost being an anti-estrogen estrogen and really helps promote that balance.