Hair follicles develop in the epidermis at nine weeks of fetal life but do not fully develop into their mature form until puberty. The hair begins to grow as a bud and continues to grow from the division of cells in the hair bulb located in the dermis.

Variances in hair texture result from differences in the shape of the hairs, as determined by the shape of the follicle and the activity of follicular cells.

Terminal hairs are the heavy, course, long, and pigmented hairs that are seen in areas of the body such as the scalp, beard, pubic area, eyebrows, and eyelashes, and axilla.

Hair color is determined by the type and amount of pigment produced by the melanocytes at the papilla, which decreases with age and causes grey hair. When white hair grows, it is the result of a lack of pigment and the presence of air bubbles in the medulla of the hair shaft.

There are three phases of hair growth: anagen (the growth stage), telogen (the resting stage), and catagen (the regression stage).

Hair is classified as vellus hair when it is soft and fine, very short, and unpigmented. These hairs have a short anagen stage and a long telogen stage.

Dermaplaning does not cause vellus hair to grow back thicker or darker.

Lasers used for hair reduction are ineffective on hair with no pigment.

Laser hair reduction only affects hairs in the anagen stage of the growth cycle, which is the reason for specific timing between treatments.