PDO treatment, a type of dermal needle therapy, is defined as inserting thread into skin lesions for the purpose of prolonging therapeutic stimulation. Recently, PDO treatment has been widely used for cosmetic purposes, such as reducing skin wrinkles and tightening facial skin, based on the belief that PDO will help to regenerate connective tissue.

PDO treatment could enhance anagen induction in the hair follicles and cell proliferation in the hair bulbus which results hair growth and improvement of hair thickness.
The hair follicle undergoes successive cyclic changes. The anagen phase starts with the first emergence of a new hair follicle in the dermis. Hair matrix cells in anagen stage, continuously proliferate and differentiate and form the hair shaft. In order to the start of anagen phase, the dermal papilla signals the multipotent epithelial stem cells in the hair buldge. This two types of cells interact continuously to enable formation and elongation of new hair shaft.
Elongation and thickening of the hair shaft occurs only in the anagen phase. Following the catagen phase leading to involution of the hair follicle, the proliferative activity of the cells in the hair matrix stops, and cell death occurs in the follicular keratinocyte. In the telogen phase, all activities in the hair follicle cease, and thick pigmented hair changes to inactive dead hair or club hair. Finally, the club hair is ejected, and a new hair emerges from the follicle, signaling the start of a new anagen phase.

Hair miniaturization, which is the characteristic feature of androgenic alopecia (AGA), is associated with shortening of the anagen phase. Therefore, drugs that extend the anagen phase can prevent hair miniaturization and are good candidate therapies for AGA.
TET increases the hair’s thickness and hair re-growth by promoting anagen induction and cell proliferation at the hair bulb. TET significantly increased the expressions of BrdU and PCNA, the markers of cell proliferation in living tissue. TET had an especially strong effect on increasing the level of PCNA at the hair bulb lesion suggesting that TET enhances the division of cells in the hair matrix, thereby increasing the hair’s thickness during the anagen phase.
Hair shaft synthesis in the anagen phase is regulated by a number of interactions between dermal papilla and the overlying follicular epithelium. Numerous growth factors and molecules are involved in the formation of the hair shaft. Among them, FGF-7 has been known to play an important role in the anagen development of hair follicles. TET increased the expression of FGF-7 at the outer root sheath.

In summary, scalp threading extends the anagen phase of the hair cycle, allowing prolonged survival of the hair shaft. Except on maintainance of the hair growth and formation and enhancement of hair thickness, TET also inhibits premature entering in the telogen phase.

Interestingly, a single application of TET resulted in hair growth comparable to that achieved with consecutive applications of minoxidil. Considering its long-lasting and proliferating potentials, TET can be considered to be a good alternative for the treatment of patients with alopecia.
At 12 weeks, all patients had appreciable degree of increase in hair counts, confirmed with investigator-evaluated improvement in GPI (40%-75%; average of 57%) , trichoscopic hair count increment (48-93 HFU/cm2; average of 67HFU/cm2).