INTRODUCTION — Skin resurfacing procedures produce improvements in skin quality, texture, and appearance through harnessing the normal wound-healing processes that follow skin injury (table 1A). Chemical peels are one of the most common facial skin resurfacing procedures; laser resurfacing, dermabrasion, and microneedling are examples of other common skin resurfacing procedures. (See "Nonablative skin resurfacing for skin rejuvenation" and "Ablative laser resurfacing for skin rejuvenation".)
The major advantages of chemical peels include the extensive clinical experience with this modality, the quickness of chemical peel procedures, relatively low cost, and unparalleled therapeutic flexibility due to the wide variety of chemical peeling agents available. Knowledge of the appropriate indications and risks of chemical peeling and familiarity with the properties of individual peeling agents are essential for counseling patients, planning treatments, optimizing results, and minimizing risk for complications.
The general principles of chemical peeling, common peeling agents, and the assessment of candidates for chemical peels will be reviewed here. Guidance on skin preparation prior to chemical peels, performance of chemical peels, and post-treatment care is provided separately. (See "Chemical peels: Procedures and complications".)
GENERAL PRINCIPLES — Chemical peels induce controlled skin injury through the application of caustic substances to the skin. The most common indications for chemical peels are actinic keratoses, solar lentigines, ephelides, dyschromias, rhytides (wrinkles), acne scars, and photoaging (table 1A). Chemical peels are typically performed on the head or neck but can be safely adapted to use on the chest, forearms, and hands .
Combining chemical peels with other cosmetic interventions is helpful in some scenarios. (See "Management of acne scars", section on 'Chemical peels' and "Photoaging" and "Melasma: Management" and "Postinflammatory hyperpigmentation".)
Mechanisms of action — The primary mechanisms of action of chemical peeling agents are the induction of keratolysis (separation of epidermal keratinocytes), keratocoagulation, and protein denaturation. Keratolysis (a mechanism of alpha- and beta-hydroxy acids) results in superficial exfoliation, which can improve skin texture and facilitate even distribution of pigment in the epidermis. Keratocoagulation and protein denaturation (a function of trichloroacetic acid [TCA] and phenol) in the epidermis and dermis lead to the release of proinflammatory cytokines and chemokines that stimulate restorative and rejuvenating effects in the skin. Examples of these effects include regeneration of keratinocytes, the production and deposition of new collagen and elastin, and the reorganization of structural scaffold proteins and dermal connective tissue .
Peel types — The depth of skin injury a chemical peel induces correlates with the clinical effects and is dependent upon the agent used and application technique. Peel depths are typically described as light (superficial), medium-depth, or deep (table 1A). The potential for more profound changes to the skin increases as the depth of the peel increases.
Light (superficial) chemical peels cause injury only to the epidermis. The effects of light peels generally consist of improving acne, skin brightening, and evening out skin color and texture. Medium-depth peels injure the epidermis and papillary dermis, allowing for both the effects of light peels and improvement in features related to abnormalities in the superficial dermis, such as mild wrinkling and mild scarring. Deep chemical peels induce the greatest degree of injury, extending into the reticular dermis. Deep chemical peels can lead to improvements in deep wrinkles and deep acne scars. (See "Management of acne scars", section on 'Chemical peels'.)
COMMON PEELING AGENTS — The depth of a chemical peel is dependent on the specific peeling agent and its mechanism of action as well as factors such as the concentration of the peeling agent, the number of applications or volume of acid applied during the treatment session, the duration of contact with the skin (glycolic acid peels), and the characteristics of skin in the treated area (thin skin versus thick, sebaceous skin).
●Jessner's solution (14% resorcinol, 14% salicylic acid, and 14% lactic acid mixed in ethanol)
Most keratolytic acid peels do not penetrate past the epidermis, making them the primary agents used for light (superficial) chemical peels. Use of high concentrations or combination treatment with other peeling agents may result in deeper peels.
Glycolic acid — Glycolic acid, a hydrophilic chemical peeling agent, is the most common alpha-hydroxy acid utilized for chemical peels and is generally used in concentrations of 20 to 70%. Light chemical peels are typically performed with 30 to 50% glycolic acid, whereas 70% glycolic acid is capable of inducing a medium-depth peel . In contrast to salicylic acid and Jessner's solution, application of a neutralizing agent (eg, sodium bicarbonate, water) is necessary to halt the action of glycolic acid on the skin.
Salicylic acid — Salicylic acid is more lipophilic than glycolic acid, allowing for better penetration through the skin's lipid layer. This characteristic may facilitate treatment of acne, as salicylic acid may offer greater penetration of acne lesions and oily skin. Salicylic acid is used for light chemical peels; typical concentrations for chemical peeling are 20 to 30%.
Jessner's solution — Jessner's solution contains 14% resorcinol, 14% salicylic acid, and 14% lactic acid mixed in ethanol. Jessner's solution has strong keratolytic effects and primary indications include acne and hyperkeratotic disorders.
Other agents — Other keratolytic peeling agents include 40% mandelic acid (an alpha-hydroxy acid), the combination of 20% salicylic acid and 10% mandelic acid, 10 to 30% lactic acid (a beta-hydroxy acid), 40 to 70% pyruvic acid (an alpha-ketoacid), retinoic acid, and resorcinol .
Protein denaturants — Protein denaturants penetrate the skin and coagulate proteins that comprise the epidermis, dermis, and blood vessels. The major protein denaturants used in chemical peels are trichloroacetic acid (TCA) and phenol (table 2).
Trichloroacetic acid — TCA has a long history of use for light and medium-depth peels and is typically applied in concentrations of 10 to 35%. The depth of TCA peels increases with the concentration of TCA and with successive applications during a treatment session. The main indications for TCA peels are photodamage, actinic keratoses, lentigines, fine rhytides, and superficial acne scars.
TCA is used both alone and in combination with other peeling agents. Risk for scarring and dyspigmentation with higher concentrations of TCA (eg, 50%) has contributed to a preference for use of lower concentrations (eg, 35% TCA) in combination with other peeling agents to achieve similar results. Combination therapy with a keratolytic agent (also known as modified TCA peels or accelerated TCA peels) allows for better control of the peel because the keratolytic agent disrupts the stratum corneum and allows for rapid and uniform penetration of TCA. Examples of keratolytic agents used in combination with TCA include Jessner's solution, glycolic acid, and solid carbon dioxide ice.
Other measures have been taken to improve the safety of TCA peels. Penetration of TCA may be slowed through use of peel products containing additional ingredients, such as glycerin and saponin. Saponin facilitates mixing of hydrophilic TCA and hydrophobic glycerin to create an emulsion that promotes even penetration of the mixture through the lipid layers of the skin.
In addition, because reapplication of TCA to a particular area augments penetration of the peel, blue dyes are included in some TCA products to facilitate tracking of skin areas in which TCA has been applied. Moreover, TCA should be acquired from a reliable source that uses the weight:volume (W:V) method to formulate the peel solution and ensure accuracy of the concentration.
Phenol and croton oil — Phenol is a protein denaturant that is primarily utilized for deeper peels. The addition of croton oil, a vesicant and epidermolytic agent, to phenol is an important determiner of the effect of phenol peels; compared with high concentration of phenol alone, croton oil promotes deeper and more uniform keratocoagulation .
Major formulations used for these peels have contained phenol, croton oil, water, and, historically, hexachlorophene and include the Baker-Gordon formula and Hetter's formula. The latter incorporates lower concentrations of croton oil (2.1% versus ≤1.6%) to improve the safety of the peel, and many clinicians now prefer Hetter's formula over the older Baker-Gordon regimen . In place of hexachlorophene, solutions incorporate surfactants containing sodium C14-16 olefin sulfonate and triclosan or polyethylene glycol (80) sorbitan laurate, based upon availability and stability [6,7].
Phenol peels result in protein denaturation extending into the reticular dermis. The primary benefit of these peels compared with more superficial peels is the induction of marked dermal neocollagenesis . Common indications include photodamage, rhytides, and acne scars. Other uses have included xanthelasma, actinic keratoses, actinic cheilitis, and lip augmentation and eversion . (See "Photoaging" and "Management of acne scars", section on 'Chemical peels'.)
Phenol peels must be performed with caution. Phenol penetrates the skin quickly, making it a difficult agent to control. Potential serious complications include cardiac arrhythmia and scarring. (See "Chemical peels: Procedures and complications", section on 'Special precautions for phenol peels' and "Chemical peels: Procedures and complications", section on 'Application'.)
INDICATIONS — The most common indications for chemical peels are reviewed in a table (table 1A). Details on the role of chemical peels for these and other conditions can be found in UpToDate topics reviewing treatment of specific conditions. Examples include:
PRECAUTIONS AND CONTRAINDICATIONS — Avoidance of chemical peels or measures to minimize risk for side effects may be indicated in the setting of increased risk for dyspigmentation, poor healing, scarring, or exacerbations of pre-existing skin disease after peeling (table 1B). Risk for these types of adverse outcomes generally increases as the depth of peeling increases:
●Increased risk for dyspigmentation – The major risk factor for cosmetically significant postinflammatory hyperpigmentation (PIH) and permanent hypopigmentation following chemical peels is moderately to highly pigmented skin (skin phototypes III to VI (table 3)). Treatment of this population with light, medium-depth, or deep peels warrants thorough counseling of patients. Patients should be informed of the potential for PIH and the need for careful adherence to pretreatment and post-treatment measures designed to reduce risk for PIH. For most patients, PIH is a temporary issue that can be remedied with topical therapies and light peels. In contrast, hypopigmentation is usually a function of depth of peeling and is, for the most part, permanent. (See "Chemical peels: Procedures and complications".)
●Increased risk for poor wound healing – Caution is necessary for medium-depth or deep chemical peeling in patients with medical conditions that can inhibit normal wound healing after the procedure. Peels of this depth should be avoided in patients with malnutrition or severe protein deficiency. Relative contraindications include other factors that may impede healing, such as smoking (tobacco, marijuana, electronic cigarettes [e-cigarettes]), history of radiation therapy in the treated area, and certain medications (eg, systemic glucocorticoids) or diseases that impair wound healing [8-10]. (See "Risk factors for impaired wound healing and wound complications".)
●Increased risk for hypertrophic or keloidal scarring – Patients with a history of hypertrophic or keloidal scarring may have increased risk for such scarring following medium-depth or deep chemical peels. We consider a history of keloidal scarring on the face an absolute contraindication for medium-depth or deep facial chemical peels. Hypertrophic or keloidal scarring in other body areas is considered a relative contraindication for medium-depth or deep facial chemical peels [11,12]. (See "Keloids and hypertrophic scars".)
●Current or recent isotretinoin therapy – The validity of the longstanding recommendation to avoid chemical peels for at least 6 to 12 months following isotretinoin therapy because of concern for increased risk for poor wound healing or scarring has been questioned [13,14]. The results of a systematic review suggest that there may not be a risk for increased scarring or poor wound healing following superficial chemical peels in patients with current or recent isotretinoin use and that delaying treatment may not be necessary [13,14]. However, more data are necessary to confirm best practices for chemical peels in this population.
Although we perform light chemical peels shortly after cessation of isotretinoin therapy, we typically avoid these procedures during the active treatment period because skin dryness and peeling related to isotretinoin may contribute to uneven penetration of the peel solution. We typically avoid medium-depth or deep chemical peels until at least three to four months have elapsed after completion of isotretinoin. (See "Oral isotretinoin therapy for acne vulgaris", section on 'Cutaneous procedures'.)
●Pre-existing skin disease – Relative contraindications for medium-depth and deep chemical peeling include active inflammatory skin conditions, such as rosacea, eczema, and acne vulgaris, in the treatment area and skin disorders that exhibit the Koebner phenomenon (induction of new lesions in sites of skin trauma) because of the potential for chemical peel-induced exacerbations. Examples of disorders that may exhibit the Koebner phenomenon include flat warts, lichen planus, psoriasis, and vitiligo.
●Active skin infection – Active skin infection is typically a contraindication to light, medium-depth, or superficial chemical peels. The compromised state of the skin barrier after a chemical peel may contribute to the spread of the infection to the treated area. The chemical peel can be performed after resolution of the infection.
●Pregnancy and lactation – Medium-depth and deep chemical peels are generally avoided in pregnant patients because chemical peels are typically elective procedures, and there are insufficient data to confirm safety in pregnancy. (See "Common problems of breastfeeding and weaning", section on 'Maternal use of medications'.)
There are insufficient data for definitive conclusions on the safety of chemical peels during lactation. Light chemical peels are likely safe, given that transmission to breast milk is likely to be minimal. We typically avoid trichloroacetic acid (TCA) and phenol peels during lactation.
●Hepatic or renal disease – Individuals with hepatic or renal insufficiency may be at increased risk for toxicity from phenol peels. Phenol is metabolized by the liver and excreted via the kidneys. Hepatic and renal disease are considered relative contraindications for phenol peels.
PATIENT ASSESSMENT — The selection of appropriate candidates for chemical peels includes not only the recognition of an appropriate indication but also an assessment for characteristics that may require a cautious approach to the procedure or avoidance of chemical peeling (table 1A-B).
History and physical examination — A focused patient history allows for the identification of patient characteristics that influence eligibility for chemical peels, risk for adverse effects, and the protocol for treatment. (See 'Precautions and contraindications' above.)
We typically obtain the following information:
●Medical history, including current and past cutaneous and systemic infections and diseases
●Current and recent medications
●History of radiation therapy in the treatment area
●History of postinflammatory hyperpigmentation (PIH), delayed wound healing, or excessive scarring (eg, keloids, hypertrophic scars) following other cutaneous procedures or injury
●History of facial surgeries that may compromise blood supply and impair wound healing
●Pregnancy and lactation status of females
A focused physical examination should include careful inspection of the area to be treated to ensure that there is an appropriate indication for chemical peeling and assess the general health of skin in the area to be treated. The physical examination should assess features that may influence the approach to treatment, including baseline skin pigmentation and signs of skin disease or abnormal scarring. (See 'Precautions and contraindications' above.)
Obtaining a history of prior treatments for the condition of concern can also help to guide the approach to treatment. Patients who have failed to achieve adequate results with previous chemical peels may benefit from a different approach to treatment.
PEEL SELECTION — Selection of an appropriate peel begins with identification of the appropriate depth of peel (light, medium depth, deep) based upon the condition being treated. Selection among the agents and peeling procedures available to achieve a particular depth may be further influenced by the specific condition, clinician comfort and experience with specific agents, and local availability of peeling agents.
Guidance on the preferred approach for specific conditions can be found in UpToDate topics that review the treatment of specific conditions. (See 'Indications' above.)
PATIENT COUNSELING — Candidates for chemical peeling should be counseled carefully regarding the nature of the procedure, preoperative and postoperative care and responsibilities, expected outcome, adverse effects, and alternatives to chemical peeling. Patient expectations for treatment results and recovery should be discussed thoroughly to ensure that expectations are appropriate. Providing sample high-quality pretreatment and post-treatment photographs of other patients with similar concerns often helps patients conceptualize expected responses.
Ultimately, patients who will proceed with chemical peeling should be able to comprehend the procedure, alternatives, risks, and expected cosmetic outcomes and should be willing and able to adhere to pretreatment and post-treatment instructions. (See "Chemical peels: Procedures and complications".)
SUMMARY AND RECOMMENDATIONS
●Chemical peels are common skin resurfacing procedures that can improve a variety of cutaneous abnormalities. The most common indications for chemical peels are actinic keratoses, solar lentigines, ephelides, dyschromias, rhytides (wrinkles), acne scars, and photoaging (table 1A). (See 'General principles' above and 'Indications' above.)
●Chemical peeling of the skin involves the induction of keratolysis, keratocoagulation, and/or protein denaturation through the application of caustic substances to the skin. A variety of peeling agents are utilized to achieve different effects on the skin. Common peeling agents include glycolic acid, salicylic acid, Jessner's solution, trichloroacetic acid (TCA), and phenol (table 2). (See 'General principles' above and 'Common peeling agents' above.)
●Chemical peels can be divided into light, medium-depth, and deep peels. Light peels induce injury limited to the epidermis. Medium-depth peels injure the epidermis and papillary dermis. Injury from deep peels extends from the epidermis to reticular dermis. (See 'Peel types' above.)
●Patients who may be candidates for chemical peels should be carefully assessed for an appropriate indication as well as characteristics that may increase risk for complications (table 1B). A focused history and physical examination can identify patients for whom precautions are indicated. (See 'Indications' above and 'Precautions and contraindications' above and 'Patient assessment' above.)
●Preparation for treatment involves selection of the most appropriate peeling agent and procedure as well as careful and thorough patient counseling. Patients who will proceed with chemical peeling should be able to comprehend the procedure, alternatives, risks, and expected cosmetic outcomes and should be willing and able to adhere to pretreatment and post-treatment instructions. (See 'Peel selection' above and 'Patient counseling' above and "Chemical peels: Procedures and complications".)
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