• TCA peels

Just as lasers offer the physician a certain level of control and safety, TCA peels have evolved in this direction as well. There have been a number of modified TCA peel combinations that were developed in an attempt to obtain more consistent results while giving the physician more control over the peel. The most common variations are Monheit’s Jessner-TCA peel, Coleman’s glycolic acid-TCA peel, Obagi’s blue peel.

These peels are designed to allow fairly consistent peeling into the papillary dermis and into the superficial reticular dermis if performed correctly. Thus, their main indications are for epidermal and upper dermal pathology such as photodamage, actinic keratoses, lentigines, ephelides, fine rhytides, and superficial, non-fibrotic (stretchable) scars. Deeper cutaneous abnormalities such as expression lines, furrows, or scars are somewhat amenable to correction with these peels. However, the risk of subsequent textural change or scarring increases with deeper peels.

• Phenol peels

Phenol peels are categorized as deep peels. Similar to TCA, phenol works through protein denaturation and coagulation. However, phenol differs from TCA in that it penetrates quickly to the level of the reticular dermis. Phenol is partially detoxified by the liver and excreted through the kidneys. Percutaneous absorption of phenol can lead to rapid elevation of serum phenol levels, resulting in systemic toxicity and cardiac arrhythmias. Therefore, all patients should be cleared from a cardiac, hepatic, and renal standpoint preoperatively. In addition, intraoperative cardiac monitoring is imperative.

Phenol peels have in the past been primarily indicated for deep rhytides in older, fair-skinned individuals because of the risk for hypopigmentation. Although any resurfacing method that reaches the reticular dermis may cause permanent hypopigmentation, the traditional Baker–Gordon peel resulted in unacceptably high rates of hypopigmentation. Weaker solutions of phenol (25–50%) can be used to achieve lighter peels, however the results are no better than TCA peels and there is still the risk for systemic toxicity. Newer modifications of phenol peels with reduced levels of croton oil have significantly reduced the amount of postoperative hypopigmentation, post-operative erythema, and scarring. Both Hetter and Stone independently described modifications of phenol peels that allow better control over depth of penetration, allowing patients of a variety skin types to be treated. These newer formulations have contributed to a recent comeback of phenol peels, as they provide physicians with clinically and financially effective alternatives to CO₂ and Erbium:YAG resurfacing.

• Modified trichloroacetic acid peels

Trichloroacetic acid (TCA) can be used to reach a variety of depths and is therefore considered the ‘workhorse’ of chemical peels. It acts by causing protein coagulation and denaturation of the cells in the epidermis and dermis as well as the blood vessels. TCA is self-neutralizing, meaning the peel will stop once it has coagulated a certain amount of protein. This is a key concept, because subsequent applications of TCA will drive the peel deeper, regardless of concentration, until the acid has coagulated proteins deeper down in the skin. Based on this knowledge, it is incorrect to refer to TCA peels as light or deep according to acid concentration.

There are four ways in which TCA can be formulated. To avoid errors in formulation, it is of utmost importance to purchase the acid from a reliable source using the weight to volume (W:V) method. The authors use a 30% TCA solution, which is then modified as part of the Obagi’s blue peel to create a 15%, 20% and 25 % solution.

In an attempt to obtain more consistent results while giving the physician more control over the peel, variations of the TCA peel (Monheit’s Jessner-TCA peel, Coleman’s glycolic acid-TCA peel, Obagi’s blue peel) have been developed (Table 11.1). Anatomically, they are designed to peel through the papillary dermis and into the most superficial aspect of the reticular dermis (Obagi’s blue peel). Their main indications are for epidermal and upper dermal pathology: photodamage, actinic keratoses, lentigines, ephelides, fine rhytides, and very superficial, non-fibrotic scars. Deeper cutaneous abnormalities such as expression lines, deep furrows, or deep scars are not amenable to correction with these peels.

Table 11.1 Summary of modified TCA peel solutions

^a Jessner’s solution: 14% resorcinol, 14% salicylic acid and 14% lactic acid mixed in ethanol

^b Obagi’s blue peel base: non-ionic blue dye, glycerin, saponin

In an attempt to speed the penetration and depth of TCA peels, two modified peels were created which incorporate the use of a keratolytic agent. Monheit described a Jessner’s-TCA peel utilizing a keratolytic acid preparation, Jessner’s solution, applied prior to the application of TCA. Jessner’s solution is comprised of 14% each of resorcinol, salicylic acid, and lactic acid mixed in ethanol. Application of the Jessner’s solution allows for faster and deeper penetration of the subsequently applied 35% TCA. A similar mechanism is employed with Coleman’s glycolic acid-TCA peel, which uses 70% glycolic acid, also acting as a keratolytic, prior to application of 35% TCA.

The Obagi’s TCA blue peel is unique in that instead of increasing the speed and depth of the peel, the process is slowed down. This allows the physician better control of depth during the peel. The Obagi’s TCA-blue peel incorporates a non-ionic blue dye, glycerin, and a saponin with a specific volume of 30% TCA to yield a 15%, 20%, or higher percentage of TCA-blue peel solution. Traditionally, straight TCA is a colorless solution that requires close attention to avoid reapplication over previously treated areas. Part of the reason for incorporating a blue dye into the blue peel solution is to stain the stratum corneum thus helping the physician to visualize even application of the peel. The saponin is an emulsifying agent that creates a homogenous TCA-oil-water emulsion that penetrates the skin in a slower and more even fashion.

• Modified phenol peels

For the most part, phenol peels fall into the category of deep peels. In a fashion similar to TCA, phenol exerts its actions by protein denaturation and coagulation; however it quickly penetrates the skin to the level of the reticular dermis. Thus, phenol peels are typically ‘quick’ peels with little time for adjusting the peel depth. There are a number of phenol peel solutions used historically with the Baker-Gordon formulation being the most recognized. Most solutions have phenol, water, croton oil, and either Septisol (Steris Corp., Mentor, OH), or other oils such as sesame seed or olive oil.

The Baker-Gordon formula resulted in impressive clinical outcomes but was fraught with about one year of postoperative erythema followed by permanent hypopigmentation. There was also a substantial risk of scarring or textural change. This limited the use of this solution to older, very fair-skinned patients.

Both Stone and Hetter evaluated the role of the different components in the various phenol solutions and they both came to the conclusion that the croton oil concentration was the most important factor in predicting the depth of skin injury (Table 11.2). Croton oil is a very strong desiccant with cytotoxic properties even in minute concentrations. Croton oil is not water-soluble but is soluble in alcohol, benzene, ethyl acetate, and chloroform. Thus it is believed that phenol, which has a benzene ring in its structure, acts as a carrier for the croton oil.

Table 11.2 Summary of various phenol-croton oil peel solutions