Translating Hair Longevity Biology into Cosmetic Science: A Narrative Review and Three-Pillar Domain-Based Framework

Abstract

Hair aging results from the parallel, interconnected decline of three biological compartments — the scalp, the hair follicle, and the hair fiber — driven by intrinsic aging processes and cumulative environmental exposure. Existing conceptual models, including the Hair Aging Hallmarks framework and integrative reviews of hair longevity biology, have clarified the mechanisms underlying this decline but have not been systematically translated into cosmetic-science action. This narrative review proposes a Three-Pillar Hair Longevity Framework — Scalp Longevity, Follicle Longevity, and Fiber Longevity — organized into eleven biologically coherent domains and modulated by two transversal, cross-domain determinants: oxidative stress/mitochondrial dysfunction and the cutaneous exposome. For each domain, the underlying biology is summarized together with the cosmetic ingredients, formulation strategies, and at-home haircare technologies with the strongest evidentiary support. The framework is restricted, by design, to cosmetic science and consumer-accessible technology; it does not address medical treatment or the management of specific hair or scalp pathologies. Its domains were deliberately defined at a level of granularity intended for direct translation into future clinical, professional, and patient-facing communication materials, without requiring reinterpretation of the underlying biology.