ELOS and laser hair removal technologies successfully achieve long-term hair reduction. Before you book your session, or if you are a physician who needs to purchase new technology in the clinic for hair removal, it is better to read the following carefully. There are three main types of hair: lanugo, vellus, and terminal hair. Lanugo hairs are fine hairs that cover a fetus and are shed in the neonatal period. Vellus hairs are non-pigmented and have a diameter of 30 mm. Terminal hair shafts range from 150 to 300 mm in cross-sectional diameter. The type of hair produced by an individual follicle can change (e.g., vellus to terminal hair at puberty or terminal to vellus hair in androgenic alopecia). Hair color is determined by the amount of pigment in the hair shaft. Melanocytes produce two types of melanin: eumelanin, a brown-black pigment, and pheomelanin, a red pigment. Hair follicles cycle through three stages: anagen, the active growth phase; catagen, in which growth stops and the cycling part of the follicle undergoes cell death; and telogen, in which hair shedding occurs. On the scalp, a typical anagen follicle continues to produce a hair shaft for 2 to 3 years giving rise to longer hair. The shorter hairs found in other body locations have correspondingly shorter anagen periods. The catagen stage of the hair cycle, lasting only a few weeks, ends as the catagen hair enters a “resting” (telogen) stage, which lasts three months. New anagen hair growth is started by cells in the bulge region. On the scalp, most hair follicles (80–85%) are in the anagen phase, and the remaining follicles are either in the catagen (2%) or in the telogen (10–15%) phase. However, in other body areas, anagen hairs may account for only 20–50% of the total number of hairs present. Telogen may last for a couple of months on the face and many months on the upper arms and legs.
Human hair growth patterns convey social information about sex, age, and racial background. Patients with hair growth abnormalities can experience considerable emotional stress and social exclusion. It is classified as either hypertrichosis or hirsutism. Hypertrichosis refers to excess hair growth at anybody’s not androgen-dependent site. Hirsutism is the abnormal growth of terminal hair in women in male-pattern (androgen-dependent) sites, such as the face and chest. Although hypertrichosis is often a primarily cosmetic problem, it may also represent a cutaneous sign of an underlying systemic disease. It can provide essential aid in diagnosing, and familiarity with its various causes is critical. One of the two important mechanisms of hypertrichosis is the conversion of vellus to terminal hairs. The surge of androgen production in adolescence causes the follicles in the axillae, groin, and, in males, the beard and chest to grow broader and deeper into the dermis and undergo conversion to terminal hairs.