Scientific Background

TCA has long since been considered the gold standard of chemical peeling agents. It is a stable agent (shelf life greater than 6 months) that is not light sensitive and requires no refrigeration. TCA crystals are naturally occurring and are mixed with distilled water to form a solution concentration measured by a ratio of weight to volume [49].By priming the skin with 70% glycolic acid, Jessner’s solution, or solid CO₂, the cosmetic surgeon can allow for penetration of a lower and safer concentration of TCA (35%) that is deeper and more evenly distributed. The end result is more uniform peeling with fewer complications. Glycolic acid at a concentration of 70% melts away the epidermal barrier by breaking up the individual keratinocytes. Jessner’s solution is composed of 14% lactic acid/14% resorcinol/14 g salicylic acid in 100 ml of ethanol.When applied, this solution destroys the epidermis in a manner similar to that of 70% glycolic acid. Solid CO₂ with acetone, however, creates epidermal necrosis, again enhancing the penetration of the subsequently applied 35% TCA. Following the chemical peel, the process of wound healing is responsible for the smoothening and tightening effect on the skin. In the immediate postprocedure phase, inflammation and coagulation are present. The inflammatory cells promote bacterial killing, granulation tissue production, and probable fibroblast growth.Within 1 day postpeel, keratinocytes have already begun to migrate from the adnexal epithelia across a fibronectin matrix.

In the 10–14 days that follow, re-epithelization is completed, as evidenced by the clinical appearance of an erythematous fresh epidermal layer. Collagen remodeling ensues, a process that may take 3–4 months after a medium-depth chemical peel [47].Histologic studies taken 3 months following a medium-depth peel demonstrate an increased grenz zone, parallel aggregates of new collagen, mucin deposition, and activated fibroblast [50]. Decreased intracytoplasmic vacuoles and spongiosis have also been seen ultrastructurally [51].


Other less popular chemicals used to achieve a medium-depth peel include pyruvic acid, and a modified Baker-Gordon peel using only one or two drops of croton oil [52]. Pyruvic acid at concentrations of 40–70% is a potent peeling agent. It physiologically converts to lactic acid, and with a pKa of 2.39, this small molecule penetrates down to the upper papillary dermis [48].Use of this agent has lead to increased production of collagen, elastin, and glycoproteins [26]. The depth of penetration of a phenol peel, as a photocoagulant, has an inverse relationship with its concentration. A phenol peel at 88% causes a barrier to be formed by precipitated epidermal proteins, which subsequently protects against deep dermal penetration [45]. At 50%, phenol is a potent keratolytic responsible for deep dermal injury.Additionally, fewer drops of the vesicant croton oil limit the penetration by decreasing the epidermolytic or drying effect.

Obagi et al. emphasize the blue peel, which uses concentrations of 15% and 20% TCA and can be used to achieve a medium-peel depth if a higher volume is used [42]. This suggests that the previous classification of peel depth cannot be determined merely by TCA concentration. One coat of a 15% TCA blue peel is said to exfoliate the stratum corneum while four coats of the same agent can peel down to the papillary dermis. This color-coded peel employs all of the properties of traditional TCA with the addition of an FDA-approved blue dye that allows even the inexperienced physician to accomplish uniform application of the peeling agent. The end points for the blue peel can be gauged by the appearance of the skin following its application. Epidermal penetration (exfoliation) is characterized by an even blue appearance without evidence of a sustained frost. The physician assumes that the papillary dermis has been reached when a frost, described as a “thin, organized, transparent sheet,” becomes visible, with the evidence of the color pink in the background (“the pink sign”). Penetration to the immediate reticular dermis is confirmed when the pink background to the frost lessens or disappears completely, giving way to a solid white sheet. This is the maximum depth recommend for the blue peel on facial skin [42].