Skin aging is accompanied by hair loss due to impairments in hair follicle (HF) epithelial progenitor cells and their mesenchymal niche. This inductive mesenchyme, called dermal papilla (DP), undergoes progressive cell loss and eventual miniaturization that contributes to HF pathogenesis. Using laser ablation and fate mapping, we show that HF dermal stem cells (hfDSCs) reconstitute the damaged DP and maintain hair growth, suggesting that hfDSC dysfunction may trigger degeneration of the inductive niche. Fate mapping over 24 months revealed progressive hfDSC depletion, and in vivo clonal analysis of aged hfDSCs showed impaired self-renewal and biased differentiation. Single-cell RNA-seq confirmed hfDSCs as a central precursor, giving rise to divergent mesenchymal trajectories. In aged skin, hfDSCs exhibited senescent-like characteristics, and senescence-associated secretory phenotypes were identified in the aging HF mesenchyme. These results clarify fibroblast dynamics within the HF and suggest that progressive dysfunction within the mesenchymal progenitor pool contributes to age-related hair loss.  Traditionally, hair restoration has been considered mainly a problem suffered by men. However, 30% of women over the age of 30 lose hair, and unlike men, who now socially can sport a shaved head, women do not have that option available to them. Full hair has been intimately tied with femininity and youthfulness, and hair loss in women can be psychologically even more debilitating at times than in men. In addition, female hair loss is oftentimes a much more complicated subject both medically and surgically speaking. Whereas oftentimes a man who presents to the clinic can be considered simply suffering from genetic male-patterned baldness, female hair loss may have a much more varied cause that demands investigation before a surgical hair transplant can be undertaken, if at all. In addition, there are nuances of surgery that must be understood to achieve excellent outcomes and requires a surgeon who is more advanced in the art of surgical hair transplant than merely a beginner. This article attempts to explore the many aspects of female hair loss and hair restoration in a highly practical manner for the surgeon and should serve as the beginning or continuation of a lifelong approach to the study of hair sciences.

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Hair Therapy and Transplantation

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