Normal Hair Growth in Children

The document from 1987 provides an in-depth look at the normal patterns of hair growth in children, from embryonic development through puberty. It explains that hair follicles originate from the epidermis around 8 weeks' gestation, with hair shafts visible by 18 weeks. The types of hair include lanugo (shed before birth), vellus, and terminal hair, with terminal hair becoming more prominent pre-puberty. The hair growth cycle consists of anagen, catagen, and telogen phases, with hair length depending on the anagen phase duration. Hair follicle density decreases with age, with males having slightly higher density than females. Initially, hair growth is synchronized, leading to waves of growth, but this changes to a random pattern by the end of the first year. The document also notes changes in hair shaft diameter and medullation with age, and slight differences in hair density and growth rates between sexes and racial groups. Boys aged 3 to 9 have a 5% to 15% faster hair growth rate than girls, and puberty triggers the change from vellus to terminal hair. Racial variations in hair form, color, and density are significant, and children's hair generally darkens with age. The review is intended to help clinicians diagnose hair disorders in children.