Topical latanoprost acid for female androgenetic alopecia: a pilot proof-of-concept trial with mechanistic evidence of prostaglandin F2α receptor activation

Background Prostaglandin F2α receptor (FP receptor) signaling is a plausible target for promoting hair growth, but clinical data on topical latanoprost acid (the active free-acid FP agonist) in hair loss are lacking. This study aimed to evaluate the clinical efficacy, safety, and mechanistic basis of topical latanoprost acid in women with female androgenetic alopecia. Methods In this investigator-initiated, randomized, double-blind, single-center, dose-ranging pilot trial, 29 adult women with hair loss predominantly consistent with female androgenetic alopecia were randomized to vehicle ( n = 2) or topical latanoprost acid 0.01% ( n = 8), 0.05% ( n = 13), or 0.1% ( n = 6), applied once daily for 6 months. The primary endpoint was within-participant change in target-area hair count (TAHC, hairs/cm²) from baseline to month 6; trichoscopic activity markers (yellow dots) and follicular-unit (FU) remodeling were secondary and exploratory outcomes. Human hair dermal papilla cells (HHDPCs) were assessed for FP receptor-linked signaling (intracellular Ca²⁺ flux) and DNA synthesis by 5-ethynyl-2′-deoxyuridine (EdU) incorporation after exposure to latanoprost acid versus equimolar latanoprost. Results An increase in TAHC was observed across all active treatment arms (mean ± SEM ΔTAHC: 17.8 ± 4.3, 23.5 ± 6.1, and 16.5 ± 6.5 hairs/cm² in the latanoprost acid 0.01%, 0.05%, and 0.1% arms, respectively). No significant between-arm differences were detected. Secondary and exploratory trichoscopic analyses showed reductions in yellow-dot counts, a decrease in single-hair FUs, and an increase in triple-hair FUs. Safety was favorable, with no serious adverse events. In mechanistic assays, latanoprost acid triggered rapid, concentration-dependent Ca²⁺ flux, whereas equimolar latanoprost produced delayed signals; neither compound altered EdU incorporation. Conclusions In this pilot proof-of-concept trial, topical latanoprost acid showed a coherent clinical-trichoscopic bioactivity signal, supported by FP receptor-linked signaling in HHDPCs. These findings require confirmation in larger randomized pharmacokinetic/pharmacodynamic-integrated trials designed to optimize dose, confirm efficacy, and further characterize long-term safety. Trial registration ClinicalTrials.gov, NCT07412587; registered on February 2, 2026.