Disclosed herein are topical compositions of 5-α reductase inhibitors, such as dutasteride or finasteride, or a pharmaceutically acceptable salt, ester, or derivative thereof and the use of the compositions for the treatment of hair loss secondary to endocrine therapy in patients with breast cancer (Endocrine Therapy-Induced Alopecia or ETIA), androgenetic alopecia (AGA), alopecia areata, and hirsutism. The topical composition is advantageous over the existing oral compositions of 5-α reductase inhibitors because the topical composition is safer and more effective. The topical formulation may allow for a slow release of the active ingredient dutasteride, better penetration at the therapeutically effective amount of dutasteride with an improved safety profile because it does not need to travel through the bloodstream to be efficacious, thereby minimizing the risk of systemic side effects.