Definition of Vellus Hair:
Vellus hair is light, short, and fine in texture and is distributed throughout the entire human body. The length and thickness of the item in question vary according to the individual. The primary purpose of vellus hair is to provide a protective barrier to the skin and retain body heat. During puberty, hormonal changes trigger the transformation of specific vellus hair follicles into terminal hair follicles, resulting in heightened hair density in those areas.

The density, color, and length of vellus hair exhibit inter-individual variation. The vellus hair of certain individuals may only be discernible when viewed nearby and under intense illumination. There is a noticeable variation in the thickness and darkness of vellus hair among individuals. Vellus hair exhibits thickness variations across different body regions (Vogt et al., 2007).
The structure of vellus hair is similar to that of terminal hair. The hair follicle serves as the origin of hair growth for both the genitalia. The sebaceous gland within each hair follicle secretes sebum, an oily substance that lubricates the skin and hair. In contrast to terminal hair, vellus hair frequently lacks a medulla. The medulla is a structural element present in the cortex of hair that facilitates robust and expeditious growth.