Chemical peeling is an aesthetic procedure intended to visibly improve the skin on the face or body via the external application of a chemical agent to induce the controlled destruction of a specific layer of the skin. It can accelerate the process of exfoliation, but it can also destroy the superficial layer of the skin or a portion of the dermis. The dead skin eventually peels off, and newer and healthier epidermal tissues are revealed. The regenerated skin is generally smoother, less wrinkled, and has pronounced improvements in terms of pigmentation and blemishes. Chemical peeling is one of the oldest forms of skin rejuvenation. It was introduced in the 1950s with the use of phenol for treating facial scars caused by acne. Peeling techniques have evolved since then with the discovery of other peeling agents, such as alpha-hydroxy acids (AHAs) and trichloroacetic acids (TCAs), both of which act on different layers of the skin and provide different results with less adverse effects and shorter downtime. Chemical peeling remains a popular treatment in aesthetic dermatology due to its flexibility and efficacy in reversing age-related cutaneous changes such as sallow complexion, pigmentation, wrinkling, and sagging. In order to select the right type of treatment for each patient, an aesthetic practitioner must possess a detailed understanding of the different types of chemical peels and their mechanisms of action, expected outcomes, potential side effects, and unwanted results, contraindications, and cautions.
When considering patients for chemical peeling, physicians and aesthetic professionals should evaluate the patients’ medical histories. Patients should be asked about their history of herpes simplex virus (HSV1 and HSV2) infection, human immunodeficiency virus (HIV) status, medication use, keloid formation, and other pertinent conditions that may affect treatment outcome. For example, some patients may be regularly applying benzoyl peroxide, an anti-acne compound that reduces the thickness of the stratum corneum, and this action can make the skin more penetrable. This is relevant because peeling acids can easily penetrate the skin, so they can cause unexpected burns. Chemical peels are generally used for cosmetic concerns and thus should be tailored to a patient’s Fitzpatrick skin type, desired outcome, and ability to tolerate a post-treatment recovery period. Essentially, a patient’s wish for a specific improvement of their skin should be weighed against realistic expectations and the careful clinical judgement of appropriate treatment options. When performing a physical examination, a physician should pay attention to a patient’s skin type and their degree of photodamage. To assess the patient’s skin, use the Fitzpatrick scale and the Glogau photoaging classification system.
Priming the Skin for Chemical Peeling
Skin priming is the foundation of an effective chemical peel. It is divided into two phases: pretreatment and preparation. The skin must be prepared at least two weeks prior to peeling. Both phases aim to thin the epidermal barrier; enhance agent penetration; reduce post-peeling side effects and complications; accelerate healing; and, more importantly, reduce the likelihood of post-inflammatory hyperpigmentation (PIH). During the pretreatment or pre-peel phase, topical agents are applied days or weeks before the procedure. The second phase includes steps that are taken directly before the actual peel, such as patient degreasing and cleansing at home and upon arrival at the clinic. Typical pretreatment regimens include the application of mild glycolic acid, salicylic acid, kojic acid, lactic acid, azelaic acid, hydroquinone, and tretinoin. A broad-spectrum sunscreen must accompany any pre-peel regimen.
Classification of Chemical Peels
Chemical peels are traditionally divided into three categories, depending on the depth of penetration and injury created. Superficial peels only act on the epidermis and can be further subdivided into superficial and very superficial, with the latter affecting the stratum corneum only. Medium-depth peels destroy the entire epidermis and the papillary dermis, while deep peels create a wound at the level of the mid-reticular dermis. The depth of chemical exfoliation is not dependent on the peeling agent but instead on a number of factors, including the concentration and pH of the solution, the mode and number of applications, the patient’s skin type, and the skin concern being treated. For example, a 70% glycolic acid is considered a superficial peel when applied for about five minutes, but it can act as a medium-depth peel if left on the skin for 15 minutes or longer. Similarly, various concentrations of TCA can be applied as a superficial, medium, or deep peel. It is now possible to combine different peeling agents to maximize the exfoliative benefits of peels and minimize adverse effects.
Medium-depth chemical peels may be used for the improvement of fine lines and wrinkles associated with sun damage, and it can also treat pigmentary disorders and textural changes, multiple keratosis, solar lentigos, and superficial scars. TCA in concentrations of 40% to 60% have been used for years, but although it is effective in these concentrations, it does have a higher risk of pigmentation and scarring. Now, the recommended medium-depth chemical peel is a combination of 35% TCA and another agent, such as glycolic acid, Jessner’s solution, and solid CO2. The use of TCA in a concentration greater than 35% is discouraged unless intentional controlled scarring is desired; this is the case when treating icepick scars.
Jessner’s solution and 35% TCA (Monheit combination)
This chemical peel combination uses Jessner’s solution, which consists of 14g of resorcinol, 14g of salicylic acid, and 14g of 85% lactic acid. Ethanol is added to come up with a 100ml solution. In preparation for the peel, the skin is scrubbed with acetone for about two minutes to remove sweat and sebum. One or two coats of Jessner’s solution is then applied to alter the permeability of the epidermal barrier and facilitate even and rapid penetration of the TCA solution. After this step, cool water compresses may be placed to treat mild burning. Additionally, topical anesthetics, such as EMLA or LMX, may be applied to improve the patient’s comfort. Apply 35% TCA after cleansing and drying the skin; this results in the formation of a speckled and white frosting and mild, uniform erythema.
Glycolic acid 70% and 35% TCA (Coleman combination)
Like Jessner’s solution, glycolic acid is keratinolytic and allows for the faster penetration of TCA. 70% glycolic acid is applied after the patient washes his or her face with water and a gentle soap. The treated areas are rinsed with cool water or neutralized with bicarbonate solution after exactly two minutes. This peel combination is effective; however, glycolic acid at 70% is not suitable for dry or inflamed skin.
Solid carbon dioxide and 35% TCA (Brody combination)
Prior to treatment, the skin is prepared with povidone iodine and the application of an alcohol wipe and an acetone scrub for three minutes. Areas that require a deeper peel, such as the glabellar lines, deep furrows around the mouth, crow’s feet, and epidermal lesions, should be marked. Solid carbon dioxide causes epidermal injury without a risk of scarring, hypopigmentation, and a deeper dermal freeze.
Mechanism of action
TCA is the principal medium-depth peeling agent and acts as a protein denaturant. As it is water soluble, it does not penetrate sebaceous skin easily; therefore, priming is required to degrease the skin, and superficial peeling may be performed to thin and increase the permeability of the stratum corneum. This step allows for a deeper and uniform penetration of chemical agents and a more even and predictable depth of protein denaturation.
The patient’s skin may feel tight and swollen, especially around the eyes, immediately after a medium-depth chemical peel is used. Some practitioners recommend the use of emollient several times a day to promote faster re-epithelialization. This typically begins on the third day, and there may be crusting and leaking of serous exudate involved. Patients should be advised that picking at the exfoliating epidermis may cause scarring. When the epidermal peeling has cleared, patients may notice a brighter and more even complexion. The process of dermal remodeling continues, resulting in the production of new collagen and an ongoing improvement in skin quality.
Deep chemical peels are mainly performed using phenol-containing solutions. TCA at concentrations of over 50% have been utilized, but higher incidences of complications makes phenol a better alternative.
Phenol deep peeling
In contrast to medium-depth peels, a phenol peel has an increased risk of scarring, PIH, hypopigmentation, and delayed healing. Additionally, phenol is directly toxic to myocardium and is rapidly absorbed into the circulation, so it carries the risk of heart failure. Full-face peels require full cardiac monitoring with intravenous hydration throughout the procedure. Administration of an antibiotic, antiviral medication, and oral steroids during the procedure is recommended. Because of the intense discomfort associated with phenol peels, patients may be treated under general anesthesia. At the very least, oral or intravenous sedation is used before and after the procedure. Phenol or carbolic acid is applied using rolled and rung gauzes. Other applicators can be used, depending on the doctor’s experience. A cotton wound around one end of a wooden skewer to form a cylinder is also ideal. The application of phenol triggers frosting. A pure white color indicates rapid frosting, while a gray-white color indicates the slower and deeper penetration of the solution into the skin.
Mechanism of action
Phenol and TCA work by penetrating through the skin, which causes coagulation and the extensive denaturation of proteins at a specific layer in the dermis. However, phenol penetrates the skin more rapidly, so it is described as a quick peel. Unlike TCA, using phenol is an aggressive form of treatment, with depth adjustments hard to achieve. Undiluted 88% phenol was originally used for medium-depth peels; however, the Baker-Gordon formula penetrates deeper than pure phenol. It combines 88% USP phenol with croton oil, septisol liquid soap, and distilled water. There are various modifications of the formula, such as the ones described by Stone and Venner-Kellson, which involve the addition of olive oil and glycerin and the modification of the concentrations of croton oil. Phenol peels are indicated for the treatment of severe photoaging, deep wrinkles, acne scarring, pigmentary disorders, and premalignant skin tumors.
Many patients treated with phenol achieved dramatic results that lasted for years. Unfortunately, the recovery period from this peel is longer and more involved than other types of chemical peeling. A non-permeable tape should be applied to the skin immediately within the first 48 hours after treatment. The waterproof mask prevents patients from touching their skin and reduces the risk of contaminating the healing skin deprived of its immune protection. During the first week of treatment, it would be helpful to keep the patient in isolation or limit their social contact to family and close relatives, as mouth movements, such as chewing and talking, can crack the developing wound. Underneath the mask, the skin will be wet and coated with exudate; this liquid is a combination of liquefied epidermal layers and inflammatory lymph. By day nine, re-epithelialization should occur, and necrotic tissues can be gently removed with emollient and the regular application of warm compresses. The regenerated skin will be swollen and erythematous for up to four weeks.
Complications from chemical peels
Medium and deep peels usually provide dramatic improvements, but several complications can also occur. The appropriate choice of peel, careful patient evaluation, pre-treatment regimen, and close monitoring of clinical signs or endpoints are important in reducing risks and occurrences of complications. Erythema may last within three to four weeks. If redness continues for more than a month after treatment, consider prior skin disease like eczema or rosacea or an unintentional deeper depth of peel. Scarring is not often seen in patients treated with medium-depth peels, but it may still occur months after the peel was applied. Identify areas with prolonged erythema and induration, as this could be a sign of potential scarring. Topical steroid application may help prevent this complication. It is common for patients with a history of herpes simplex infection to develop herpetic lesions. Antiviral prophylaxis is recommended for high-risk patients. Deeper peels are not indicated for dark-skinned individuals, because the likelihood of permanent hypopigmentation. If it occurs, the application of 4% hydroquinone, a lightening agent, can help.
Patients who wish to reverse skin aging without undergoing surgery may choose from several chemical peeling options instead. During consultation, assess a patient’s desired outcome and the degree of photodamage present. The Glogau scale and Fitzpatrick classification system are two important assessment tools to use while deciding if your patient is a good candidate for chemical peeling. The Fitzpatrick classifies skin types based on their colors and reaction to the sun’s UV rays. The Fitzpatrick classification system shows how melanocytes behave in each individual and if chances of hypopigmentation, PIH, and scarring are high in certain people. Although chemical peels are minimally invasive, thoroughly evaluating a patient’s medical history is necessary to recognize underlying diseases, medications, and practices that will influence the results of the peel. This treatment is not only doctor-dependent or agent-dependent, as it also depends on a patient’s willingness to be involved in his or her own care. A pre-treatment regimen and post-treatment wound care must always be performed. Finally, the efficacy of chemical peeling is dependent on the experience of the practitioner performing the procedure. A practitioner with experience with chemical peeling is likely to yield better results than a novice peeler.