Current understanding and treatment of sex hormone-related hair diseases

Hair follicle (HF) growth is regulated by local and systemic environments. Sex hormones, a systemic factor, paradoxically promote and suppress hair growth in different sites of the body, leading to diseases such as hirsutism, androgenetic alopecia, and female pattern hair loss. The past decades have seen progress in the treatment of sex hormone-related hair diseases, but the pathogenesis of some of these diseases remains obscure and even controversial. We review the biological effects of major sex hormones on hair growth and summarize their known impacts. We discuss the different responses of animal and human HFs to sex hormones, summarize the pathogenesis of sex hormone-related hair diseases, and highlight the benefits of and controversies in the current management of these diseases. Finally, we discuss future research directions such as interactions between sex hormones and the immune system and the possible role of epigenetics in these hair disorders.