The Story
The field of hair restoration is a dynamic specialty where advanced technologies allow surgeons to achieve more aesthetically pleasing results. Hair loss appears to have troubled humanity since the dawn of history, as evidenced by a recipe for restoring hair that was included in the 1500 BC Ebers Papyrus of ancient Egypt.
The success of modern hair transplantation depends on a phenomenon first described by Orentreich in 1957 called donor dominance. With this phenomenon, hair taken from the permanently haired area of patients with androgenetic alopecia (donor area) and transferred to the hairless areas (recipient area) of the scalp, continues to grow in its new location for as long as it would have to continue growing in the area from which it was taken.
The hair
Hair varies among ethnic groups and in each individual. It has two separate structures: the follicle embedded within the skin and the part of the hair that is visible on the surface of the body. In addition, there are several types of hair.
Most hair shafts emerge from the scalp as individual hair clusters—4. Clusters are the visible surface portion of the follicular unit (FU) and usually consist of one to four terminal hair follicles and one vellus follicle. The direction of the hair differs depending on the part of the scalp on which it grows.
Therefore, both the direction and angle of the incisions must be adapted to be consistent with the direction of the hair in a specific scalp area.
Hair cycle
The hair follicle is a dynamic organ whose cyclical activity requires regeneration and reassembly of the non-permanent portion of the hair follicle during each cycle. Normally, the amount of new scalp hair formation is equal to the amount that is lost, thus maintaining consistent coverage.
The hair follicle cycle goes through three main phases: a growth phase (anagen), an active phase, a regression phase (catagen) and a resting phase (telogen).
Recently, two additional stages in the follicular cycle have been identified: the release phase (exogenous) and the lag phase (kenogen). Furthermore, it is the type of follicle and its physical location that determine the length of each follicular phase.
Hair loss or disorder
Diseases that cause hair loss are classified by two important factors: the spread or location of hair loss and the existence of a healthy follicle.
In general, the factors that cause hair loss are inflammation, genetics, environment and hormones.
Androgens
Androgens paradoxically have different effects on human hair follicles, these effects being dependent on their location in the body. Testosterone is the circulating androgen in men that when reduced to dihydrotestosterone (DHT) by a 5α-reductase enzyme, binds to the androgen receptor. In hair follicles, the 5α-reductase enzyme, androgen receptors (AR) and AR coactivators may regulate androgen sensitivity. In hairless scalps, the 5α-reductase enzyme and androgen receptors are increased.
Androgenetic alopecia (AGA) or male pattern hair loss (MPH)
AGA, also known as male pattern alopecia, is the most common cause of hair loss, affecting up to 70% of men by mid-adulthood. APM occurs in the presence of androgens in genetically susceptible individuals. The recent increase in the level of prostaglandin D2 in hair follicles has been suggested as one of the main causes of APM.
The key feature of APM is follicular miniaturization whereby the duration of the active growth phase is reduced from 2–6 years to a few months, and the resting phase is relatively elongated. The new generations of hair are consequently shorter, finer, and lighter in color and typically obscure the scalp to a lesser extent. The transition may be gradual or may come in waves; however, the course and extent of APM are unpredictable.
In men, the pattern usually begins with bi-temporal recession, followed by vertex baldness and mid-frontal hair loss, allowing retention of terminal hair follicles in the occipital region of the scalp. The most commonly used system to assess MPA is the Hamilton-Norwood scale.