Answer:
Trichloroacetic acid solution was one of the first agents developed for chemical peeling. TCA ranges in concentration from 10% to 50%. Concentrations less than 10% produce little effect. Concentrations greater than 50% have an exceedingly high risk of scarring. In contrast to phenol it produces no systemic toxicity. Trichloroacetic acid is a keratocoagulant. As one increases the concentration, a “frost” or whitening of the skin appears. The whiteness intensifies as the concentration increases. Although the concentration of TCA correlates with the depth of destruction, it is not an absolute indicator since multiple variables must be considered. Concentrations of TCA ranging between 10% and 25% are used for superficial peels. The depth of injury is intraepidermal. The entire stratum corneum is removed as well as a significant portion of the epidermis. Since the depth of destruction is superficial, there is a correspondingly low risk of scarring. As one increases the concentration of TCA to 30% or 40%, the injury reaches the papillary dermis. Classically, this is considered a medium-depth peel. Once the TCA concentration rises above 40%, it is considered a “deep” peel. At this higher concentration the risk of scarring is significantly increased. The higher concentrations of TCA should be used with great caution. A level of deep destruction seems to be achieved with less risk with other methods such as phenol, dermabrasion, or ultrapulsed carbon dioxide laser surgery. Before performing a TCA peel, it is advantageous to have “primed” the skin for several weeks before a peel with Retin-A or glycolic acid. Doing this will maximize the benefits of the peel as well as make the overlying stratum corneum thinner and more compact prior to the peel. The patient is placed on a surgical table with the back tilted to 45 degrees. The hair is either taped back with paper tape or a surgical cap is placed on the head. The skin is carefully inspected for abrasions, cuts, or other injuries that would require modification in technique. (Applying acids to nonintact skin produces unpredictable results). Once the skin has been inspected, it is thoroughly cleaned with acetone, alcohol, or another degreasing agent to remove surface lipids so that acid is absorbed more uniformly. It is preferable to have an assistant in the room to pull the skin taut for the application of acid into deep furrows and wrinkles and blot the lateral canthi when tearing develops. If tears are not adequately dabbed from the area, they can run down the cheeks and leave tracks of diluted acid in their path. Additionally, osmotic capillary action can “wick” acid in a retrograde fashion back into the eye. Two-inch by two-inch gauze sponges are saturated with the acid and squeezed to the point at which almost no more acid drips from the gauze. The patient’s head is tilted to the right and stabilized with one hand. The acid is then applied with smooth, slightly overlapping, long brush-like strokes. It is first applied to the left side of the forehead and brow. The peel is extended up into the hairline and down into the eyebrow. Dry gauze is used to immediately remove some of the excess acid that adheres to the eyebrow hair. If this is not done, there is an additional reservoir of acid, which can then come down onto the skin and lead to a deeper peel in that area. Once the left forehead and temple have been treated, it is wise to wait for a brief interval to assess the degree of frost as well as its rapidity of onset. The left infraorbital and cheek skin are peeled next. The eyelid skin must be held under tension so that precise control of acid application can be achieved. When acid is applied to the infraorbital skin, the patient gazes superiorly to minimize any potential corneal injury. The next area peeled is the left upper lip and left side of the nose. The final area on the left side is the left lower lip, chin, and jawline. It is important to bring the chemical peel under the ramus of the mandible so that any lines of demarcation between peeled and unpeeled skin will be hidden in its shadow. It is ideal to apply less acid here and “feather” the solution since the skin is often thin overlying the mandible and submandibular region. Once the left side of the face has been completed, the patient’s head is gently tilted to the left, and the right side of the face is treated. After the peel is completed the skin is observed for development of a frost. If after inspection the frost is not as deep as anticipated, it is appropriate to retouch those areas. For this purpose, it is prudent to reduce the concentration of acid by 10% to diminish the cumulative effects of reapplication. During the entire peeling process, a fan can be used to aid in patient comfort. Once the peel has been completed and the frost has reached a plateau, cool water compresses are applied, which patients find soothing. This is not meant to neutralize the TCA but merely to dissipate some of the generated heat. The final phase of a TCA peel is the postpeel wound care. Patients should expect their skin to feel tight and drawn over the days following the peel. The skin will darken noticeably and areas of previous hyperpigmentation will show an even greater tendency to darken. Initially, because of the mobility of the skin around the mouth, the skin first starts to peel at the oral commissures. It is vital that patients be instructed not to pull, pick, or in any other way disrupt this newly separating skin. If the strips of skin are annoying to them, they can simply trim the loose edges with a clean pair of cuticle scissors. Pulling at the skin carries the risk of creating a deeper wound and potential scar. Patients should clean their faces very delicately with mild soaps. Astringents and other alcohol-based compounds are to be avoided since they will cause premature drying of the skin and can be quite irritating. When the skin is cleansed during the healing phase, it should be done delicately, and the skin patted rather than rubbed dry. Emollients are used to accelerate healing. The method of application is more critical than the choice of emollient. It must be performed in a way that does not disrupt the newly healing skin. Ointments that are too stiff or thick are difficult to apply and are to be avoided. The skin is in its most vulnerable state at this point and unnecessary additives and chemicals should not be used. Simple products such as Vaseline ointment are inexpensive and effective. Following a chemical peel, sun exposure is to be avoided. Sweating and exercise are contraindicated. It is not only uncomfortable but increases the chance of infection. If the patient is having significant itching at night, it is often helpful to administer an oral antihistamine to avoid inadvertent scratching of the skin during sleep. Satin pillowcases may be helpful in reducing friction on the newly healing skin for patients who turn onto their face at night. Depending on the depth of the peel, complete wound healing can require anywhere from 5 to 14 days. Once the skin has re-epithelialized, it will remain pink. This pinkness or erythema can persist for several months before the patient’s normal skin color returns.
Although TCA can be used to peel nonfacial skin, this must be done with caution. Healing is aided by the presence of appendageal structures. Since these are abundant on the face and ample blood flow is present in this area, healing proceeds quite well. On nonfacial skin wound healing is much slower and scar formation is more frequently seen. For this reason, decreased concentrations of TCA with repeated peels represent a prudent course of action.