Ultrastructure of hairs in healthy children during development: a preliminary study

Abstract

Objective To characterize the morphology and structure of hair surfaces and cross sections in children of different ages, and to understand the development and maturation processes and status of hairs in terms of ultrastructure in healthy children after birth. Methods Ninety healthy child volunteers were equally classified into 3 groups: infancy group (aged less than 1 year), toddler group (aged 1 - 2 years), and preschool-age group (aged 3 - 5 years). Hair samples were collected from the vertex, tempus, and occiput of each child. Field emission scanning electron microscopy was performed to obtain morphological data on surfaces and cross sections of hairs, including minimal and maximal hair diameters, hair index (the ratio of minimal to maximal diameter of hairs), hair cuticle thickness (measured on hair cross sections, each hair has 5 - 10 layers of cuticles), hair cuticle count (the number of cuticles per 100 μm length of hair shaft) and pattern (flat waveform or irregular shape). Statistical analysis was carried out by using analysis of variance, t test, chi-square test, and least significant difference (LSD) test with SPSS19.0 software. Results The minimal and maximal cross-sectional diameters of hairs significantly differed between the three age groups at the same anatomic site (vertex: F=39.67, 28.32, respectively, both P < 0.01; tempus: F=13.12, 11.91, respectively, both P < 0.01; occiput: F=18.41, 16.43, respectively, both P < 0.01), and increased with age, while no significant changes occurred in hair index with age. Meanwhile, significant differences were observed between the three age groups in the thickness of hair cuticles on the vertex (F=6.15, P < 0.01), and in the number of hair cuticles on the vertex, tempus, and occiput (F=3.29, 3.36 and 3.48 respectively, all P < 0.05). LSD test showed a significant difference in minimal and maximal hair diameters between the infancy group and toddler group and between the infancy group and preschool-age group (all P < 0.001), an elevation in the thickness of hair cuticles on the vertex in the preschool-age group compared with the infancy group (0.59 ± 0.09 vs. 0.49 ± 0.08 μm, P=0.003), but a decrease in the number of hair cuticles on the vertex, tempus and occiput in the preschool-age group compared with the infancy group (all P < 0.05). No significant differences were observed between male and female volunteers in minimal and maximal hair diameters, hair index or hair cuticle thickness and number at the same anatomic site. In addition, there were no significant differences in the distribution of the two hair cuticle patterns between the three age groups. Conclusions Hair diameter and cuticle thickness both increase, while hair cuticle number decreases, with the development of children. Key words: Hair; Infant; Child, preschool; Child development; Microscopy, electron, scanning