Topical Thyroid Hormones Promote Hair Follicle and Epithelial Hair Follicle Stem Cell Growth in Intact Human Scalp Skin Ex Vivo

This study investigates the effects of topically applied thyroid hormones, triiodothyronine (T3) and thyroxine (T4), on hair growth in human scalp skin ex vivo. Using scalp skin from 3 male donors, the researchers applied T3 and T4 in various concentrations for 6 days. The results showed that topical T3 and T4 significantly increased the percentage of hair follicles in the anagen phase and the proliferation of hair matrix keratinocytes. Additionally, they increased the expression of hair growth-promoting proteins FGF-7 and IGF-1, while not affecting the catagen-promoting TGFβ-2. The study suggests that topical thyroid hormones could be a promising treatment for hair loss disorders, warranting further clinical trials.