Introduction

• The problem being treated

This chapter discusses chemical peeling indications, associated complications and expected results in darker skin. Chemical peeling is a form of skin resurfacing that induces epidermal and/or dermal injury/destruction followed by regeneration of epidermal and dermal tissues. The benefits seen with chemical peeling vary in different ethnic and racial groups. Many agents are available for chemical peeling today. In ethnic skin, efforts are focused on superficial and medium-depth peeling agents and techniques. Dermatologists should be confident that the peeling agent has a documented safety profile as well as efficacy in darker skin types. It is interesting that, while the majority of the world has this particular skin type, there is little information in literature regarding peeling agents and techniques in dark skin individuals. Since darker skin has its peculiarities, dermatologists should be particularly careful when performing cosmetic procedures in this skin type.

The usual classification of chemical peels comprises superficial, medium and deep peels. For superficial peels, AHA, Jessner’s solution, tretinoin, TCA in concentrations of 10–30% and most recently lipo-hydroxy acid are used to induce an exfoliation of the epidermis. Medium-depth agents such as TCA (30–50%) cause an epidermal to papillary dermal peel with subsequent regeneration. Deep peels using TCA (>50%) or phenol-based formulations penetrate the reticular dermis to induce dermal regeneration. The success of peeling in darker skin is crucially dependent on the physician’s understanding of the chemical and biological processes, as well as of indications, clinical effectiveness and side effects of the procedure (see Box 9.1).

• Patient selection

Dark skin as well as ethnic skin, brown skin, black skin and pigmented skin are terms used to describe skin of color. Such individuals are classified as Fitzpatrick’s skin types IV through VI. Over the years, this racial group has been increasingly interested in cosmetic procedures. In 2008, this patient group had approximately 20% of all cosmetic procedures. When considering cosmetic procedures in darker racial groups, dermatologists should be aware of the special characteristics, as well as structural and physiologic differences in the skin of such individuals. These differences can significantly affect and influence cosmetic surgical outcomes.

Skin color depends largely on the content and distribution of melanin in the epidermis. The melanocytes of darker skin, in particular black skin, produce more epidermal melanin. In black people, the melanosomes are larger, distributed singly within keratinocytes, and persist up to the stratum corneum. Comparative studies showed some differences between epidermis of black and white people. Although the stratum corneum has an equal thickness in both groups, in black skin there are more cell layers and it has an increased resistance to stripping compared to white skin. Moreover, the stratum corneum of darker skinned people has greater intracellular cohesion, higher lipid content and an increased electrical resistance compared to white skin counterparts. While there is no difference in corneocyte surface area between black and white skin people, desquamation was up to 2.5 times greater in black skin. The epidermis of dark skin is more effective at blocking the transmission of ultraviolet radiation than white skin epidermis due to increased content of epidermal melanin, which confers greater intrinsic photoprotection. An interesting study showed significant differences in the amount of ceramides in the stratum corneum amongst various racial groups. The lowest levels are in black people followed by progressively higher levels seen in white, Hispanic, and Asian people. Darker skin recovered faster after barrier damage induced by tape stripping. Clinically darker skin types are frequently plagued with dyschromias due to the labile responses of cutaneous melanocytes. Main stratum corneum differences between black skin and white skin are depicted in Table 9.1.

Table 9.1 Comparison of stratum corneum characteristics between black skin and white skin

Characteristic	Black skin	White skin
Thickness	=	=
Number of cell layers	↑	↓
Lipid content	↑	↓
Electrical resistance	↑	↓
Desquamation	↑	↓
Corneocyte surface area	=	=
Ceramide content	↓	↑
Resistance to stripping	↑	↓
Recovery from stripping	↑	↓

=, equivalent; ↑, higher; ↓, lower

While chemical peeling is an excellent modality to treat photodamage associated skin changes in Fitzpatrick skin types I and III, the main indications for chemical peeling in skin types IV–VI are dyschromias, postinflammatory hyperpigmentation (PIH), acne vulgaris, scarring, melasma, and pseudofolliculitis barbae as well as textural changes and oily skin (Box 9.2). Despite major concerns regarding peel complications in darker skin such as PIH, hypopigmentation and scarring, recent studies suggest that peelings, particularly superficial peels, can be performed safely in darker groups.

• Expected benefits

Chemical peeling can be used to improve the appearance of ageing, wrinkled or sun-damaged skin. The degree of skin improvement resulting from a chemical peeling depends on the depth of the peel. Peel depth should be adjusted to correlate with the depth of the pathological process to be treated. For example, actinic lentigines are characterized by elongation of epidermal rete ridges with focal excess melanocytes and melanophages with concomitant increased melanin production. Complete elimination of these common lesions requires at least a medium-depth peel. Sun-damaged skin shows epidermal changes, elastosis, and collagen distortion in the midreticular dermis. To eradicate moderate to severe photodamage, deep peels are required. More superficial peels, even when performed in repetitive fashion, do not reach the affected histological level and therefore have a minimal effect on photodamaged skin. Also, superficial peels are less effective in treating acne scars. However, analysis of morphologic, physiologic, and clinical data suggests that the benefits of chemical peeling in dark skin can be optimized by utilizing superficial peels while also simultaneously minimizing risks. Given the labile nature of melanocytes of darker skin individuals, medium-depth and deep peels are more likely to induce substantial complications and side effects and the authors do not recommend these peels in darker skin.

Superficial peels, which are generally epidermal and pose little risk of scarring, are usually performed in multiple weekly or monthly applications for maximum efficacy. Interim home care products are recommended to augment and prolong benefits. The main clinical results for superficial peels in darker skin include improvement of skin texture and superficial dyschromias. Although minimal postoperative care is needed for superficial peels and patients may return to their normal daily activities immediately, compliance with pre- and postpeel treatment is essential. The patient must be motivated to adhere to a daily skin regimen for a few weeks before and after the procedure. The patient must also be able to tolerate the erythema and scaling that occur after a peel. In addition, patients must avoid the sun before and after a peel.

Although the technique of chemical peeling is relatively simple, great care must be taken to minimize possible side effects. Potential complications of chemical peels include: pigmentary changes, infections, milia, acneiform eruption, hypopigmentation, scarring, and cardiotoxicity. While most of these adverse events are fortunately rare, they occur more frequently following medium and deep peelings.

Patients with skin types IV–VI have a higher risk of PIH, even with low concentrations of superficial peeling agents. Abnormal pigmentation may develop very soon after the peel or months later, and it is often the result of poor technique or early sun exposure after the peel. Other causes of PIH include estrogens, photosensitizing drugs or pregnancy. Sun avoidance and the daily use of broad spectrum sunscreen are very important for its treatment, especially in darker skinned patients. Oral contraceptives may exacerbate hyperpigmentation, and if possible, they should not be used during the peripeel period. Also aggressive chemical peelings should be avoided in pregnant patients. Epidermal PIH responds well to various treatments, whereas dermal hyperpigmentation is more resistant. Bleaching agents such as hydroquinone and kojic acid may be used to gradually lighten the pigmentation, and are especially effective when used in combination with retinoic acid or alpha hydroxy acids (AHA) products, which promote exfoliationof the epidermis. Cautious titration of peeling agents is also recommended in darker skinned types. It is best to start with low concentrations of peeling agents in dark skin. In comparison to superficial TCA (25–30%) peels, superficial peels such as tretinoin, glycolic acid, salicylic acid and Jessner’s induce a lower frequency of postprocedure complications.

Overview of Treatment Strategy

Chemical peels can be classified by the depth of penetration into the skin (Table 9.2). Superficial peelings (epidermis to upper papillary dermis) are the most commonly used peels in all phototypes. These agents include tretinoin 1–5%, TCA 10–35%, glycolic acid solution 30–50% or glycolic gel 70%, salicylic acid 20–30% in ethanol and Jessner’s solution (Combes’ formula).

Table 9.2 Types of peels by depth

Peel Type	Depth (µm)	Examples
Superficial	100	Glycolic acid (buffered); salicylic acid; Jessner’s; TCA 10–15%; Combination peels: TCA + salicylic acid; Jessner’s + salicylic acid; Vi Peel^™; Nomelan fenol kh; Melanage^™
Medium	200	Glycolic acid unbuffered; Jessner’s; Jessner’s + 20% to 35% TCA; Hetter VL (phenol)
Deep	≥ 400	Hetter all around; Stone 100 (grade 2); Exoderm-Lift