The structure and function of the hair and skin can certainly be impacted by low or high levels of thyroid hormones, such as the active hormone T3 and the prohormone T4, the main product of the thyroid gland.95 However, the specific mechanism by which T3/T4 stimulation affects human hair follicles, and whether an increase or decrease in T3 and/ or T4 levels directly influences the development of alopecia, are yet to be known. The gene discussed is TG; the disease is alopecia.