Pérez-Romero AG, Sánchez-Dueñas LE, Aceves-Villalvazo MA, Morfín-Hernández L

Language: Spanish
References: 18
Page: 99-105
PDF size: 220.47 Kb.

ABSTRACT

BACKGROUND: The human hair follicle is a highly specialized organ whose cyclic activity determines the structural characteristics of the hair shaft according to the anatomical region. Despite its clinical relevance, quantitative data regarding growth kinetics and cycle duration remain dispersed across medical and forensic literature.
OBJECTIVE: To integrate and systematize available evidence on the anatomical variability of the follicular cycle, hair elongation rates, and the distribution of terminal versus vellus hair, contrasting adult physiology with pediatric follicular maturation.
RESULTS: The review establishes that the scalp exhibits the most prolonged cycle (anagen phase of 2–8 years) with a consistent growth rate of 10 mm/month. In contrast, regions such as eyebrows and eyelashes display brief growth phases (2–3 months and 4–10 weeks, respectively), functionally adapted for ocular protection. Complementary forensic studies reveal differential growth rates in the axilla (≈0.4 mm/day) and pubis (≈0.3 mm/day). In the pediatric population, growth velocity shows an age-dependent evolution, accelerating from 0.22 mm/day in infants to 0.38 mm/day by age three.
CONCLUSIONS: Human hair biology is defined by a functional duality: it follows a strict regional anatomical programming but retains plasticity in response to the microenvironment. The final clinical length depends not only on growth kinetics but is also modulated by molecular signaling networks (Wnt/BMP), neuroendocrine balance, and the cumulative impact of the exposome on the hair fiber.

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