22 Chemical Peels

Rebecca Small, MD, and Kathleen O’Hanlon, MD

Chemical peeling is a skin resurfacing procedure that utilizes topical agents to remove the outermost layers of the skin.¹ This controlled method of wounding stimulates a reparative healing response with regeneration of a healthier epidermis and dermis. Chemical peeling, also called chemexfoliation, is commonly used for skin rejuvenation to improve photodamage, reduce hyperpigmentation and acne, and smooth rough skin texture and superficial scarring.²

As with all skin resurfacing procedures, deeper penetration into the skin is associated with greater potential benefits. However, risks and complications also increase with greater depths of penetration into the skin. The depth of penetration achieved with chemical peels ranges from the superficial epidermis to deep dermis. Standard terminology for skin resurfacing depths is illustrated in Figure 19-12 in Chapter 19, Aesthetic Principles and Consultation. The focus of this chapter is light chemical peels, which include very superficial chemical peels that remove the stratum corneum, and superficial chemical peels that remove the entire epidermis and may extend to the upper papillary dermis.³

Chemical peels are one of the most common cosmetic procedures performed in the United States, ranking closely behind botulinum toxin, laser hair removal, and dermal fillers, according to data from the American Society for Aesthetic Plastic Surgery.⁴ They are technically straightforward to perform and, with minimal start-up costs, they are often one of the first aesthetic procedures incorporated into office practice.^1,⁵ Chemical peels can be readily combined with other minimally invasive aesthetic modalities such as microdermabrasion, topical products, and nonablative lasers to enhance skin rejuvenation results.

Patient Selection

While almost any patient will derive benefit from light chemical peels, patients with mild to moderate photoaging changes such as solar lentigines, skin dullness, rough texture ⁶^–⁸ (e.g., Glogau types I and II), and acneic conditions^9,¹⁰ typically derive the most noticeable benefits (see Chapter 19 for a description of Glogau types). Results with light chemical peels are slow and progressive, requiring a series of treatments for improvements to become evident. Light peels may also improve fine lines, coarse pores, and superficial atrophic scarring,⁷ but results are not comparable to more aggressive forms of skin resurfacing, such as medium-depth peels or laser resurfacing. Assessment of patients’ expectations at the time of consultation and commitment to a series of treatments is essential to ensure success with these treatments.

Very superficial chemical peels (e.g., glycolic acid 20%, salicylic acid 20% and retinol) can be used in all skin types (Fitzpatrick types I through VI). Patients with darker skin types (IV through VI) have increased risks with aesthetic procedures, particularly postinflammatory hyperpigmentation, and these gentle peels are one of the treatment options available to manage aesthetic skin conditions in darker skin types such as acne, enlarged pores, and hyperpigmentation (see Chapter 19 for a description of Fitzpatrick skin types).¹¹^–¹⁴ A conservative approach for providers getting started with superficial chemical peels (e.g., glycolic acid 70%, trichloroacetic acid 20% to 30%, and Jessner’s 4 to 7 layers) is to restrict use of these peels to lighter skin types (Fitzpatrick types I through III) to minimize the risk of complications.

Patients with erythematous conditions such as rosacea, telangiectasias, and poikiloderma of Civatte are also treated conservatively with light chemical peels, as aggressive chemical peels may exacerbate erythema associated with these conditions.¹⁵

Indications

• Photodamaged skin

• Hyperpigmentation (e.g., solar lentigines, melasma, postinflammatory hyperpigmentation)

• Dull, sallow skin color

• Comedonal acne (whiteheads and blackheads); also called clogged pores or skin congestion by laypersons

• Papulopustular conditions including acne vulgaris, acne rosacea, pseudofolliculitis barbae

• Rough skin texture

• Enlarged pores

• Fine lines

• Atrophic scars (e.g., acne and chicken pox scars)

• Keratosis pilaris

• Thickened scaling skin (e.g., ichthyosis)

• Early thin seborrheic keratoses

• Actinic keratoses

• Enhanced penetration of topical products.

While the superficial and very superficial peels discussed in this chapter are appropriate for the above indications, some subtle trends for selecting one peel over another exist with regard to indication. Salicylic and glycolic acid are often used for oily skin and acneic conditions; lactic acid for dehydration; mandelic acid for sensitive skin; and retinoids for augmenting other peels they are combined with to enhance skin sloughing.

Alternative Therapies

Microdermabrasion (MDA) is comparable to a superficial chemical peel in terms of the depth of resurfacing, and is a reasonable alternative treatment for skin rejuvenation. MDA offers certain advantages over chemical peels such as greater control over the depth of exfoliation, comparatively less discomfort, and no “downtime” for skin flaking and peeling. However, MDA equipment is more costly than chemical peels. Superficial dermaplaning, which uses a specialized scalpel blade that is gently scraped across the skin, is another alternative method of exfoliation and is particularly useful for patients with erythematous conditions such as rosacea.

Deeper skin resurfacing can be achieved using more aggressive procedures such as medium-depth chemical peels or laser resurfacing. Laser resurfacing may be performed as an ablative procedure, where the epidermis is removed (e.g., with the 2940 nm wavelength), or as a nonablative procedure, where the epidermis remains intact (e.g., with the 1550 nm wavelength). Relative to light chemical peels, laser resurfacing and deeper chemical peels offer significantly greater reduction of wrinkles and improvements in photodamaged skin. However, these more aggressive resurfacing procedures have longer recovery times and greater risks of complications.

Light chemical peels will not improve deep wrinkles related to volume loss and hyperdynamic musculature, which respond to treatment with dermal fillers and botulinum toxin, respectively.

Products Currently Available

Numerous chemical peels are available and common agents, along with their typical depth of skin penetration, are summarized in Figure 22-1.¹⁵^–¹⁸ Many factors influence the depth of penetration with chemical peels, and although a given chemical peel may be classified as a superficial peeling agent, in practice, peels may vary in the depth of penetration. Figure 22-1 is, therefore, intended only as a general guide for chemical peel depths.

FIGURE 22-1 Chemical peel agents and depth of skin resurfacing.

Chemical Peel Depth of Penetration

The depth achieved with light chemical peels ranges from very superficial resurfacing with removal of the stratum corneum, to superficial resurfacing with penetration to the upper papillary dermis. Although the type and concentration of chemical agent used are the main determinants of the depth of penetration in the skin, other factors also influence the depth of penetration including ¹⁹:

• Chemical peel agent

• Concentration

• pH

• Application time (i.e., the duration for which the peel is in contact with the skin)

• Application technique (e.g., application pressure)

• Quantity (e.g., number of layers)

• Skin preparation (e.g., previous skin resurfacing procedures, topical products used at home prior to procedure)

• Skin type (e.g., thick sebaceous or thin dry skin)

• Area of the body treated (e.g., face, neck, back).

Alpha Hydroxy Acids

Alpha hydroxy acids (AHAs) are derived from organic fruit acids and include: glycolic (sugar cane), lactic (milk), malic (apples), tartaric (grapes), citric (citrus), mandelic (almonds), and phytic (rice) acids. These products are keratolytic and penetrate through the stratum corneum, causing exfoliation by disrupting corneocyte adhesion. AHAs in more acidic formulations (i.e., lower pHs) and in higher concentrations have stronger biologic effects. Glycolic acid peels typically have a pH of 2.5 to 3. Very low pHs (pH < 2) of glycolic acid, however, are associated with greater risk of necrosis and crusting, and do not offer improved results over less acidic preparations.²⁰ AHAs found in topical products as part of daily skin care regimes typically contain low AHA concentrations (10% or less) in less acidic formulations (pH 3.5 or greater).

Glycolic acid (GA) is the most commonly used AHA and is an agent frequently selected by providers getting started with chemical peels.¹² Glycolic acid is a small, water-soluble molecule that readily penetrates the skin. GA peels are clear colorless solutions that do not change in appearance upon application to the skin, unlike salicylic acid for example. Figure 22-2 shows GA applied to the dorsum of one hand, and salicylic acid on the other hand with its characteristic white precipitate. Because GA chemical peels do not exhibit a reliable clinical endpoint that is visible, application must be carefully monitored and timed, and the acid neutralized at the appropriate point to control the procedure. Clinical response to glycolic acid can be variable. Some patients have a brisk inflammatory response to low-strength (20% to 35%) short-duration applications (1 to 3 minutes), whereas others may tolerate higher strengths (70%) for longer duration (up to 7 minutes). The effects of GA can be terminated after application through neutralization, which raises the pH and renders the acid ineffective. Neutralization of alpha hydroxy acids may be performed with water or sodium bicarbonate solution (5% to 15%). If neutralization is not performed, AHAs will continue to be active and may penetrate deeper than intended.

FIGURE 22-2 Salicylic acid (on the left) produces a white precipitate or pseudofrost, while glycolic acid (on the right) is clear and colorless.

(Copyright Rebecca Small, MD.)

Beta Hydroxy Acids

Salicylic acid (SA), derived from willow bark, is a lipophilic, slower penetrating acid than GA. For the purposes of this chapter it will be classified as a beta hydroxy acid, but it should be noted that in the purest chemical terms, the hydroxyl group of beta hydroxy acids is neutral and in salicylic acid it is acidic. SA dissolves and reduces sebum, has anti-inflammatory effects, and is FDA approved as an anti-acne therapy.

The benefits of SA as compared to the AHAs include less stinging, because SA has a mild anesthetic effect; a visible clinical endpoint with a fine white precipitate (“pseudofrost”), which helps ensure even application (see Figure 22-2), and no requirement for neutralization. Once a white precipitate is formed, there is little additional penetration of the acid and water may be used to wash off the precipitate. A disadvantage of SA is more obvious post-treatment desquamation than with GA. SA peels are available as pure or combination products, and instructions for application and endpoints vary based on the product used. For example, La Roche-Posay’s Biomedic SA peel 30% ends with frosting, whereas SkinCeutical’s SA/Mandelic Peel (SA 20% combined with mandelic acid 10%) does not frost.

Trichloroacetic Acid

Trichloroacetic acid (TCA) is an agent familiar to many clinicians who have used it as therapy for condylomata acuminata (in highly concentrated preparations of 80% to 90%). For superficial chemical peels, it can be used as pure TCA 10% to 30%, or in combination with other peeling agents, such as TCA 15% combined with lactic acid 10%, or TCA 15% combined with SA 15% and lactic acid 15%. After application, TCA causes skin erythema and a whitish discoloration called frosting, which occurs 30 seconds to 2 minutes after application. Histologically, frosting corresponds to coagulation of epidermal proteins and keratinocytes. The intensity of frosting correlates directly with the depth of penetration (see Table 22-1).²¹ The desired clinical endpoint for superficial depth peels with TCA is level I frosting, visible as patchy erythema with faint white coloration.

TABLE 22-1 Frosting with Trichloroacetic Acid Chemical Peels and Depth of Penetration

Frosting	Depth of Penetration	Clinical Findings
Level I	Superficial	Patchy erythema with faint patchy white color
Level II	Medium	Even white color with some erythema visible through the white
Level III	Deep	Opaque confluent white

The technique for application of TCA is very important because the depth of penetration is dependent on the application quantity. It is usually applied in multiple consecutive applications, called layers, with a period of 2 to 3 minutes of observation for clinical endpoints between layers. Neutralization is not required with TCA, but water may be used at the end of the treatment to remove the white precipitate. Frosting usually disappears within 1 to 2 hours and erythema becomes more evident. A disadvantage of pure TCA is that it has significant post-treatment peeling and may be more painful than SA and GA peels. However, combination TCA chemical peels, as listed above, do not appear to be more uncomfortable than other superficial peel agents. A well-known TCA peel is the Obagi Blue Peel™, which has TCA 20% peel formulated with a blue-colored base containing glycerin and saponins to slow penetration and release of TCA in the skin.

Jessner’s Solution

Jessner’s solution is a combination of resorcinol 14%, salicylic acid 14%, and lactic acid 14% in ethanol, which was originally developed to lower the concentration of any one agent and, hence, reduce the risk of toxicity.²² Modified Jessner’s formulations are also available that have no resorcinol, such as salicylic acid 14%, lactic acid 14%, and citric acid 8% in ethanol (e.g., PCA Peel^®). Once applied, erythema is followed by a powdery whitening of the skin due to precipitation of salicylic acid. Neutralization is not required, but water may be used to remove the white precipitate. Jessner’s peels are frequently applied in multiple layers, with a period of 4 to 7 minutes of observation for clinical endpoints between layers. Figure 22-3 shows a patient with mild erythema and a faint whitish coloration after application of six layers of a Jessner’s peel.

FIGURE 22-3 Jessner’s peel immediately after application of six layers, showing mild erythema and faint white skin coloration from the salicylic acid precipitate.

(Copyright Rebecca Small, MD.)

Retinoids

Topical retinoids, such as tretinoin (Retin-A) and tazarotene (Tazorac), have been principal therapies for acne and skin rejuvenation for many years as part of home skin care regimes. More recently, retinoids have been used as superficial peeling agents ranging from tretinoin peels 0.05% to 1%²³ to lower strength preparations containing retinol (e.g., retinol 15% combined with lactic acid 15%). Retinoid peels cause a yellowish discoloration after application. They are not neutralized and are typically washed off by the patient 8 hours after application. Retinol peels may be layered over other superficial peeling agents (such as glycolic and salicylic acids) to enhance desquamation. Figure 22-4 shows a patient immediately after application of six layers of Jessner’s peel followed by one layer of retinol 15% peel combined with lactic acid 15% peel with characteristic yellow skin coloration.