Introduction

Chemical peels are a method of resurfacing the skin. By inducing a controlled wound to the skin, chemical peels replace part or all of the epidermis and can induce collagen remodeling which helps to improve photodamage, rhytides, pigmentation abnormalities, and scarring. Chemical peels are divided into three categories depending upon the depth of the wound created by the peel (Boxes 2.1 and 2.2). Superficial chemical peels penetrate the epidermis only, while medium-depth peels damage the entire epidermis plus the papillary dermis to the level of the upper reticular dermis. Deep chemical peels create a wound to the level of the mid-reticular dermis. Each category of peel addresses a different aspect of photodamage and pigmentary abnormality. Healing time and complications vary among the different categories of peel as well, with some peels being more appropriate for certain skin types. Therefore, in order to maximize the benefits of a peel for a patient and to minimize adverse effects, it is important to choose which, if any, peel is appropriate for each patient. See also Box 2.3.

Evaluation of the Patient

When evaluating a patient for a peel, an extensive history should be taken. The patient should be questioned regarding a history of herpes simplex virus infection, human immunodeficiency virus (HIV) status, keloid formation, previous x-ray therapy of the skin, nicotine use, oral isotretinoin use, and a history of a previous facelift or browlift. Patients with a history of herpes simplex virus should be treated prophylactically to prevent an outbreak of herpes. Patients infected with HIV are poor candidates for a peel because their immunocompromised state delays wound healing and increases the risk of wound infection and subsequent scarring. Patients who have been treated with oral isotretinoin should wait 6–12 months after completion of the treatment since there is some evidence that isotretinoin also inhibits wound healing and can induce atypical scarring. Similarly, patients who have recently had a facelift or browlift should wait 6–12 months before undergoing a medium or deep peel. Extensive undermining during facelifts compromise the skin’s blood supply and, thus, wound healing is delayed. Superficial x-ray therapy to the skin destroys the pilosebaceous units which, in turn, leads to delayed reepithelialization, while nicotine use decreases the blood supply to the skin and delays wound healing. Both of these underlying factors can result in an increased risk of scarring.

The physician should also perform a physical examination and pay particular attention to the patient’s skin type and degree of photodamage. Skin type can be classified using both the Glogau photoaging classification and the Fitzpatrick skin type scale (Box 2.4 and Table 2.1). Together, these skin classification systems can be used to objectively assess the patient’s skin and are an important component in choosing the appropriate peel. The Glogau photoaging classification system is used to quantify photodamage. Patients with Glogau type I skin would benefit most from a superficial peel, while those with Glogau type IV skin would benefit from deep peels. The Fitzpatrick skin type scale can be used to predict how a patient’s pigmentation will respond to each specific chemical peel. Patients with Fitzpatrick skin types I and II can usually be treated with all chemical peels safely and successfully, while care must be taken in those patients with Fitzpatrick skin types III to VI, since patients with these skin types have a much higher risk of developing postinflammatory hyperpigmentation (PIH; Fig. 2.1).

Table 2.1 Fitzpatrick’s classification of sun-reactive skin types

* Asian Indian, Oriental, Hispanic, or light African descent, for example

Figure 2.1 Patient with Fitzpatrick skin type VI. Patient would have an increased risk of developing postinflammatory hyperpigmentation following certain chemical peels

The physician should also note the sebaceous quality of the skin as well as the presence of any inflammatory skin disorders, such as seborrheic dermatitis or psoriasis. Patients with very sebaceous skin may require additional prepeel degreasing of the skin in order to achieve the same depth of penetration of the peeling agent as patients with very thin, nonsebaceous skin. Patients with an underlying inflammatory skin disorder will have increased absorption of the peel and may inadvertently sustain a deeper peel than intended; in addition, they may develop a hypersensitivity syndrome following a chemical peel, and patients with psoriasis may exhibit the Koebner phenomenon after a peeling procedure. Other important factors for a physician to consider when evaluating a patient for a chemical peel would include the use of sunscreen and topical retinoids. There has been some evidence that the use of topical tretinoin preoperatively can help to induce more rapid healing after a chemical peel procedure. Patient education regarding sunscreen use will help to minimize the risk of PIH and will help to mitigate further sun damage.

Perhaps the most important discussion that a physician must have with a patient preoperatively is one regarding realistic expectations. Without doubt, eliciting clearly a patient’s chief complaint is of the utmost importance and can prevent any misunderstanding after the operation. The physician should realistically describe the postoperative course, healing time, anticipated results, and potential risks of the procedure. If a risk of PIH exists, hydroquinone should be used preoperatively to reduce the chance of that occurring.

Superficial Chemical Peels

Superficial peels can be categorized further into ‘very light’ and ‘light’ peels. See Box 2.5.

• Very light chemical peels

These include 10–15% trichloroacetic acid (TCA), alpha-hydroxy acid (AHA), beta-hydroxy acids such as salicylic acid, topical tretinoin, and one to two coats of Jessner’s solution (14% resorcinol, 14% salicylic acid, 14% lactic acid, and ethanol). These peels penetrate the stratum corneum and possibly the upper layers of the stratum spinosum. Because of the very superficial depth of penetration of these peels, they tend to be safe and appropriate for all skin types, but still must be used judiciously.

While a single treatment of a very superficial peel can induce exfoliation, a series of these peels is necessary in order to achieve additional benefit. Improvement of skin texture, through the removal of the stratum corneum, induction of acanthosis and an increase in thickness of the granular layer, as well as improvement of melasma and solar lentigenes can be achieved through a series of very superficial peels (Fig. 2.2). PIH is not common with superficial peels as they create minimal inflammation, but can occur.

Figure 2.2 Patient with melasma. Patient would be a good candidate for treatment with a series of superficial chemical peels

Glycolic acid, AHA, and salicylic acid peels may be helpful in the treatment of acne vulgaris. These peels are keratolytic and can help to alleviate comedones. Salicylic acid, in particular, is helpful in the treatment of acne because it is lipophilic and penetrates the sebaceous units. Scaling, erythema and PIH are temporary and usually resolve with no long term effects. In patients with Fitzpatrick skin types IV to VI, the use of salicylic acid as a very light chemical peeling agent seems to result in a much lower incidence of PIH. Very light peels can also be used prior to starting topical 5-fluorouracil (5FU) therapy for actinic keratoses. By inducing an exfoliation of the stratum corneum, these very light peels allow an increased penetration and effectiveness of 5FU.

Medium Depth and Deep Chemical Peels

Medium-depth chemical peels include combination peels such as solid CO₂ plus TCA or Jessner’s solution plus TCA. Some authors also include 88% phenol as a medium-depth peeling agent, but others classify it as a deep peel. Historically, 50% TCA was used as a medium-depth peel, but the development of many complications such as scarring and PIH limited its use, although the use of 50% TCA is quite effective in the treatment of isolated lesions such as xanthelasma.

‘Combination peels’ have replaced 50% TCA as the gold standard for medium-depth peels. These peels combine a superficial peeling agent, such as Jessner’s solution or 70% glycolic acid, with 35% TCA. This combination induces a similar depth of penetration as 50% TCA without an increased risk of complications. Combination medium-depth peels are more effective in treating actinic keratoses, rhytides, melasma, seborrheic keratoses, and solar lentigines, and a greater improvement of skin texture is achieved than with superficial peels. However, patients with Fitzpatrick skin types IV to VI have a greater risk of PIH when undergoing a medium-depth peel compared to a superficial one. Postoperatively, patients experience erythema and desquamation of the skin which resolves in 8–10 days. On account of the associated risk of renal and cardiac toxicity, 88% phenol is rarely used as a medium-depth peeling agent, although, by performing the peel slowly over 1 hour and by using intravenous saline, the risk of systemic absorption of the phenol can be decreased. Nevertheless, the patient’s cardiac status must still be monitored throughout the procedure.

Treating actinic keratoses with a medium-depth peel produces results comparable to topical 5FU; however, the treatment course is much shorter with a medium-depth peel (i.e., one peel versus 4 weeks of topical application). The healing time is also much faster. Specifically, patients heal in approximately 1 week after undergoing a medium-depth peel, but treatment with topical 5FU can result in 3–4 weeks of recovery. Medium-depth peels can also be used to blend the skin after laser resurfacing of the periorbital and perioral regions. Patients with Fitzpatrick skin types I to III are most appropriate for medium-depth peels; patients with skin types IV to VI will probably experience PIH, which may last for years. Hydroquinone or Kojic acid, used either before or after the peel, may be effective in treating PIH. Medium-depth peels can improve skin texture and rhytides. Histologically, this is evidenced by an increase in the amount of glycosaminoglycans and elastin in the dermis and an increase in the Grenz zone.

Patients with acne and rosacea may not benefit from a medium-depth peel. Rosacea patients may experience prolonged erythema while patients with acne may experience a flare-up due, perhaps, to swelling and inflammation induced in their skin or to the use of heavy emollients as part of the postpeel regimen.

Deep chemical peels are comparable to CO₂ laser resurfacing and are most appropriate for Fitzpatrick skin types I and II. These peels dramatically improve deep rhytides, acne scarring, and skin laxity. However, due to the depth of penetration and the direct melanotoxic effect of phenol, a significant percentage of patients develop permanent postinflammatory hypopigmentation. Hypopigmentation is usually not as noticeable in lighter skinned patients (Fitzpatrick skin types I and II), but in patients with darker skin types this can be devastating. Deep peels include the Baker-Gordon peel, which is composed of croton oil, phenol, and Septisol liquid soap. Postoperatively, deep peels produce erythema and crusting for up to 14 days.

Summary

In conclusion, chemical peels are a safe and inexpensive method of resurfacing the skin. However, it is critical for the physician to choose the appropriate peel for the appropriate patient in order to achieve the desired end point and to decrease the risk of complications. Superficial peels are safe in virtually all skin types. These peels can effectively treat melasma, acne vulgaris, thin seborrheic keratoses, and lighten solar lentigenes. They may also induce subtle changes in skin texture. Medium-depth peels are most safely used in Fitzpatrick skin types I–III. Patients with Fitzpatrick skin types IV–VI can be treated with medium-depth peels, but the risk of PIH is greatly increased. Deep peels can dramatically improve deep facial rhytides, acne scarring, and photodamage. Because of the high incidence of postpeel hypopigmentation, these chemical peels are most appropriate for patients with Fitzpatrick skin types I and II.