There are 3 types of wires and these are Lanugo hairs that fall out after birth, thin Vellus hairs scattered throughout the body, and thicker and longer Terminal hairs. Hair has 3 concentric areas: the cortex, which is the largest part of the hair, the cuticle that covers the cortex from the outside, and the medulla, which is the central area of the hair. In general, hair grows by 10 to 15 mm each month and this growth is dynamic. This hair growth consists of 3 phases:
The anagen phase is the growth phase in which the hair grows actively, approximately 84% of the hair is in this phase and lasts for 3 to 10 years. The catagen phase is the phase in which the hair strands stop growing, about 1% of hair is in this phase and lasts for 2 to 3 weeks. Telogen phase is the phase in which there is no activity or hair growth in the hair bulb, approximately 15% of the hair strands are in this phase and lasts for 3 to 4 months. In humans, these 3 phases occur simultaneously in different hairs. In general, every human hair goes through 10 to 20 complete cycles (as anagen - catagen - telogen) during their average lifespan (Cheong et al., 2017).