Xenoestrogen
Xenoestrogens are a type of xenohormone that imitates estrogen. They can be either synthetic or natural chemical compounds. Synthetic xenoestrogens include some widely used industrial compounds, such as PCBs, BPA, and phthalates, which have estrogenic effects on a living organism even though they differ chemically from the estrogenic substances produced internally by the endocrine system of any organism. Natural xenoestrogens include phytoestrogens which are plant-derived xenoestrogens. Because the primary route of exposure to these compounds is by consumption of phytoestrogenic plants, they are sometimes called "dietary estrogens". Mycoestrogens, estrogenic substances from fungi, are another type of xenoestrogen that are also considered mycotoxins.
Estrogen and neurodegenerative diseases
Nonsteroidal estrogens include xenoestrogens, phytoestrogens and mycoestrogens. They are very useful in neurodegenerative diseases' therapy when considering about the side effects caused by estradiol. 
As the development of chemical synthesis, it becomes possible for people to construct new molecules. Drug companies can exploit naturally existing compounds and synthetic compounds that have estrogen-like activity to produce patented proprietary drugs, especially the contraceptives. 
Phytoestrogens are plant derived estrogens and have similar structures with 17beta-estradiol thus may cause estrogenic or anti-estrogenic effects.