Chapter 88. Hair Growth Disorders

Effluvium:

Active process of hair shedding

Alopecia:

Loss of hair, reduced hair density (scalp or body)

Terminal hair:

Large hair follicle with a thick, medullated hair shaft >30 μm, roots are located in the subcutaneous fat

Vellus hair:

Very small colorless non-medullated hair (<30 μm, roots are located in the upper dermis), only a few mm long. Vellus hairs can be found on the entire body except for palms and sols in different densities, depending on the body site.

Vellus-like hair:

Hair that evolves from a former terminal hair follicle that had been miniaturized (due to androgenetic alopecia or alopecia areata), very small colorless hair (<30 μm, roots are located in the dermis), fibrous tissue (fibrous streamer) replaces the former terminal follicle below the root down to the subcutaneous fat

Intermediate hair:

Hair in a transition stage from terminal to vellus-like due to a miniaturization process (∼50–30 μm, roots are located in the deeper dermis)

Lanugo hair:

First hair produced in utero, pigmented, around 2–3 cm long, lanugo hairs are usually shed between week 32–36 of gestation but can be still present at birth in one third of children

Hirsutism:

Growth of terminal hair on the body in a male distribution in women

Hypertrichosis:

Increased growth of terminal hair or growth of lanugo hair on the body in an androgen-independent pattern

Canities:

Graying of hair

Canities subita:

Sudden (over night) graying of hair, appears in diffuse alopecia areata, when white hairs are spared by the inflammation and remain on the scalp while dark hair falls out very quickly

Poliosis:

Localized white hair

Cicatricial alopecia:

Irreversible hair loss, with loss of follicular ostia, and potentially skin atrophy

Hair cycle:

Life-long cyclic transformation of hair follicles, which begins in utero

Anagen:

Active growth phase, duration and growth rate depend on the body site (around 3–6 years on the scalp)

Telogen:

Resting period, the hair shaft does not grow longer; duration depends on the body site (around 3 months on the scalp)

Catagen:

Apoptosis driven regression phase between anagen and telogen

Exogen:

Process of hair shaft shedding

Anagen hair:

Hair with a pigmented root (except in white hair) and an inner root sheath (shows the form of a golf club ...