Two types of estrogen receptor are distinguishable in the human hair follicle. Estrogen receptor α is involved in keeping the hair follicle in anagen (growth activation of the hair follicle), while estrogen receptor β is responsible for inducing telogen in preparation for the hair to be shed. In humans estrogen receptor α is the predominant estrogen receptor in hair follicles.
Due to the mixed ability of coumesterol to interact with estrogen receptor α and estrogen receptor β, this compound is able to exert actions that increase hair follicle growth. Human estrogen (17 β — estradiol) tends to interact with estrogen receptor β (the primary estrogen receptor in the hair follicle).
Phytoestrogens can act as an anti- estrogen by temporarily binding to estrogen receptor β, thus inhibiting the telogen inducing activity of human estrogen by blocking binding sites. This means coumesterol can prevent activation of estrogen receptor β and reduce premature telogen and extend anagen phase.
Substrates binding to an estrogen receptor usually have a preferential affinity to one receptor type. In this regard, the majority of phytoestrogens show a preference for estrogen receptor β, while coumesterol predominantly binds to estrogen receptor α.