Chemical peels: A review of current practice

Australasian Journal of Dermatology (2018) 59, 171 181 doi: 10.1111/ajd.12715 REVIEW ARTICLE Chemical peels: A review of current practice Alicia A O Connor, 1 Patricia M Lowe, 1,2 Stephen Shumack 2,3 and Adrian C Lim 2,3 1 Department of Dermatology, Royal Prince Alfred Hospital, 2 Sydney Medical School, University of Sydney, and 3 Department of Dermatology, Royal North Shore Hospital, Sydney, New South Wales, Australia ABSTRACT Chemical peels belong to a group of cutaneous resurfacing procedures that are used in the treatment of photoageing, inflammatory dermatoses, epidermal proliferations, pigmentary disorders and scarring. This review describes best current practice, highlights recent advances in chemical peel technology and discusses the recommended uses for different peel types. It also presents the results of a survey of the chemical peeling practices of 30 Australian dermatologists. Key words: acne vulgaris, chemabrasion, facial rejuvenation, photoageing and pigmentary disorders. INTRODUCTION Over the centuries numerous techniques have been employed to reverse the ravages of age and the effects of cutaneous disease. 1 Among these methods, chemical peeling has withstood the test of time with superficial peels in particular remaining a popular tool in the dermatology therapeutic armamentarium (Table 1). Chemical peels consist of the application of one or more chemical ablative agents to the skin s surface in order to induce keratolysis or keratocoagulation. 1,2 This process causes the controlled destruction of all or part of the epidermis or dermis, resulting in the subsequent exfoliation of these layers. 2 4 After wounding, regeneration and remodelling Correspondence: Dr Alicia A O Connor, Department of Dermatology, Royal Prince Alfred Hospital, Gloucester House Level 3, Missenden Road, Camperdown, NSW 2050, Australia. Email: aliciaann.oconnor@health.nsw.gov.au Alicia A O Connor, MBBS. Patricia M Lowe, FACD. Stephen Shumack, FACD. Adrian C Lim, FACD. Conflict of interest: none. Submitted 24 April 2017; accepted 16 July 2017. of the epidermis and dermis ensues, leading to the improved appearance and texture of the treated skin. 5 Dermatologists frequently use chemical peels to treat an array of cutaneous conditions, including acne vulgaris, actinic or solar keratoses, melasma and scarring. This technique has also been used to rejuvenate the skin of the face, neck, trunk and hand. Peeling agents may be divided into superficial, medium-depth and deep subtypes based on the depth of their penetration (Fig. 1). They may be used alone or in combination with other cosmetic procedures for cutaneous aesthetic enhancement. Synonyms for chemical peels include chemabrasion, chemexfoliation, chemical exfoliation, chemical face lifting, chemosurgery, dermapeeling, facial rejuvenation and surface surgery. 1,6 In this article we review the history, classification, mechanism of action, indications, contraindications, complications and general principles of chemical peels. Furthermore, we examine recent advances and future directions in this field. Finally, we present the results of a survey of the chemical peeling practices of 30 Australian dermatologists. CLASSIFICATION OF CHEMICAL PEELS Chemical peels are classified according to their depth of penetration of the skin into superficial, medium-depth and deep subtypes (Table 2). The depth of penetration is determined by the concentration, ph and type of peeling agent used. 28,29 Anatomical location, epidermal integrity, adnexal structure density and skin thickness also influence the depth of the peel. 28 Other important considerations include cutaneous priming, application technique, occlusion and contact time. 1,28,30 Superficial peels target the epidermis and the epidermal-dermal interface causing partial or complete necrosis. 28,31,32 They exfoliate the skin from the stratum corneum down to the papillary dermis at a depth of 60 lm. 4 Superficial chemical peels work by causing decreased corneocyte adhesion, epidermolysis and increased dermal collagen deposition. 31 34 This results in Abbreviations: AHA BTX-A TCA alpha hydroxy acid botulinum toxin-a injection trichloroacetic acid

172 AA O Connor et al. Table 1 History of chemical peels Year Source Comment 1500 BC Ebers papyrus Ancient Egyptians used alabaster, animal oils, salt, honey & sour milk for cutaneous aesthetic enhancement 7 9 1871 Tilbury Fox 20% Phenol to lighten skin 8,10 1874 von Hebra Iodine tinctures, croton oil, mustard seed, cantharides, sulphuric acid, acetic acid, nitric acid, hydrochloric acid, borax, alkalis & corrosive sublimate for disorders of increased pigment 8,11 1881 Piffard Croton oil to induce inflammation 8 1882 Gerson Unna Described properties of phenol, resorcinol, salicylic acid & TCA 10 1892 Saalfeld Phenol for ephelides 8 1903 & 1952 Mackee Phenol for acne scars Histological changes with phenol peeling 12 1941 Eller Salicylic acid, resorcinol, acetone, formaldehyde solution, beta naphthol, phenol, glacial acetic acid, sulphur, mercurial salts, & solid CO 2 for pitted scars & pigmentation 13 1945 Monash Diluted TCA to treat acne scars, molluscum contagiosum, xanthelasma palpebrarum, tinea versicolor & lichenified eczema 14 1946 Urkov Salicylic acid, resorcinol, lactic acid and ethyl alcohol solution under tape occlusion for superficial peeling; deep exfoliation with cantharides tincture & phenol 15 1950 Jessner Alcohol-based solution of lactic acid, salicylic acid & resorcinol for superficial peeling 8 1960 Ayres Diluted TCA superior to pure phenol for extensive superficial peeling 16 1960 Brown, Kaplan, & Brown Histological changes, technique & complications of phenol peeling 17 1962 Litton Phenol, glycerin, distilled water & croton oil solution for facial rejuvenation 18 1960s Baker & Gordon Phenol-based formula containing Septisol, distilled water & croton oil for facial rejuvenation 19 22 1984 Van Scott & Yu Alpha hydroxy acids for hyperkeratinisation disorders 23 1986 Brody & Hailey TCA 35% + solid CO 2 for medium-depth peeling 24 1989 Monheit Jessner s solution + TCA 35% for medium-depth peeling 25 Late 1980s L Oreal Recherche C8-lipohydroxy acid 26 1994 Coleman III & Futrell Glycolic acid 70% + TCA 35% for medium-depth peeling 27 CO 2, carbon dioxide; TCA, trichloroacetic acid. Figure 1 Depth of chemical peel penetration. the thinning of the stratum corneum, increased epidermal thickness and a more even distribution of melanin. 32,35 Superficial peels are suitable for all Fitzpatrick skin phototypes and may be used on extra-facial sites such as the upper limbs, neck and chest. 3,28 Serial application is often required. Examples of superficial peeling agents include 10 30% salicylic acid, 20 70% glycolic acid, Jessner solution, solid carbon dioxide slush and <20% trichloroacetic acid (TCA). Medium-depth peels penetrate the papillary dermis to the upper reticular dermis at a depth of 450 lm. 4,5,34 They cause extensive protein precipitation, resulting in coagulative necrosis of cells in these layers. 34 This produces oedema and homogenisation of the papillary dermis. 36 Medium-depth peels are typically performed as a one-off procedure. 5,37 Desquamation occurs over 5 days and patients can return to work after 1 week. 6 TCA 35 50% is a commonly used medium-depth peeling agent. 34 TCA 35% may also be combined with glycolic acid 70%, Jessner solution or solid carbon dioxide to form a combination medium-depth peel. 34 Deep peels penetrate to the mid-reticular dermis at a depth of 600 lm. 3,31 They denature epidermal keratin and dermal proteins, causing complete epidermolysis and mid-

Chemical peels 173 Table 2 Classification of chemical peels Superficial Medium Depth of penetration Peeling agent Conditions Stratum corneum to papillary dermis 60 lm Papillary dermis to upper reticular dermis 450 lm Alpha-hydroxy acids (glycolic acid 20 70%, lactic acid, malic acid, pyruvic acid, tartaric acid); beta hydroxy acids (salicylic acid 10 30%), carbon dioxide snow, Jessner solution, lipohydroxy acid, resorcinol, retinoic acid, TCA <20%, Unna paste, 5-fluorouracil TCA 35 50%, TCA 35% + solid CO 2, TCA 35% + glycolic acid 70%, TCA 35% + solid CO 2, TCA 35% + Jessner solution Mild photoageing (actinic keratoses, fine lines, roughness, solar lentigines, yellow stains), acne vulgaris, mild acne scarring, pigmentary disorders (melasma, mild dyschromia, post-inflammatory hyperpigmentation) Mild-to-moderate photoageing, actinic keratoses, fine lines, rhytides, solar lentigines, pigmentary disorders, (melasma, mild to moderate dyschromia) seborrhoeic keratosis, superficial atrophic scars Deep Mid-reticular dermis to 600 lm Baker Gordon, TCA >50% Severe photoageing (advanced rhytides), pigmentary disorders, premalignant skin tumours, scars CO2, carbon dioxide; TCA, trichloroacetic acid. dermal injury. 6,31,35 Deep chemical peels are single-session rather than serial procedures. Wound healing occurs in four distinct phases including inflammation, coagulation, re-epithelisation and fibroplasia. 38 Re-epithelisation occurs after 10 14 days, with the patient being able to return to work in 2 3 weeks. 35,39 Erythema may persist up to 3 months. 6 Examples of deep-peeling agents include concentrations of TCA greater than 50% and Baker Gordon formula. 31 SUPERFICIAL PEELING AGENTS Alpha hydroxy acids Alpha hydroxy acids (AHA) constitute a family of carboxylic acids with a hydroxyl group attached at the alpha position of the carboxyl group. 26 They are derived from fruit such as apples (malic acid), grapes (tartaric acid), lemons and oranges (citric acid), sugar cane (glycolic acid) and milk (lactic acid). 30 At lower concentrations, AHA causes decreased corneocyte adhesion. 33,40 At higher concentrations it promotes epidermolysis. 33,40 AHA requires neutralisation to terminate its action. This is achieved with water, sodium bicarbonate, sodium hydroxide or ammonium salt solutions. 30,41 AHA do not induce a frosting pattern. Glycolic acid is the most common AHA peeling agent. 41 It is available as an esterified, buffered, partially neutralised or free acid solution. 41 Glycolic acid has a pka of 3.83 and is soluble in water. pka is an important concept in chemical peeling. It is the ph at which half of the solution is in a free acid form. 42 A low pka value indicates a greater availability of free acid and hence a stronger peel. 42 Beta hydroxy acids Salicylic acid Salicylic acid (also known as ortho-hydroxybenzoic acid) is a naturally occurring beta hydroxy acid that is derived from the sweet birch, wintergreen leaves and willow tree bark. 5,30 It has a pka of 2.97 and is poorly soluble in water. 28,43 Salicylic acid differs from AHA by the presence of a hydroxyl group at the second carbon atom position. It destroys intercellular lipids that are covalently linked to the cornified envelope surrounding cornified keratinocytes. 28 This results in the desquamation of the stratum corneum and the activation of basal keratinocytes and fibroblasts. 28 Salicylic acid has mild analgesic, antimicrobial, keratolytic and comedogenic anti-inflammatory effects. 28,30 For superficial chemical peeling, salicylic acid is used in concentrations of 10 30% in a hydroethanolic or polyethylene glycol base. 28 It is applied to the skin for 3 5 min, causing a fleeting burning sensation before its analgesic properties prevail. 5,28 Evaporation of the hydroethanolic base leaves a white precipitate often mistaken for frosting. 28 It is important to note that salicylic acid peels do not induce a frosting pattern or require neutralisation. 28 They also have a theoretical risk of salicylism if they are applied to large surface areas at one time. 5,28 Salicylic acid peels are favoured for use in comedonal and inflammatory acne, as well as for oily skin. 28 Lipohydroxy acid C8-lipohydroxy acid (also known as capryloyl salicylic acid, 2-hydroxy-5-octanoyl benzoic acid or b-lipohydroxy acid) is a lipophilic derivative of salicylic acid. 32 It consists of an 8-carbon acyl fatty chain that is attached to the fifth carbon of the benzene ring. 26 Lipohydroxy acid targets corneodesmosome protein structures to separate corneocytes uniformly. 31,32 Its increased lipophilicity means it has a more targeted mechanism of action in the epidermis and sebaceous follicle and a greater keratolytic effect than salicylic acid. 31 Lipohydroxy acid is used in concentrations of 5 10% and does not require neutralisation. 31 It also has antimicrobial, anti-inflammatory and non-comedogenic properties. 31 Jessner solution Jessner solution consists of salicylic acid (14 g), resorcinol (14 g), lactic acid 85% (14 g) and ethanol (100 ml q.s.). 33 It

174 AA O Connor et al. is a clear, amber-coloured solution that needs to be kept in a brown bottle to prevent photo-oxidation. 28,30 Jessner solution is generally applied in two to three coats before mild erythema and delicate, patchy frosting develops. 28,40 It does not require neutralisation. 40 Patients may experience a burning sensation with this peeling agent. 28 It can be used as a preparatory peel to enhance the penetration of another peeling agent such as TCA. Pyruvic acid Also known as acetyl formic acid, pyruvic acid is an a-keto acid that differs from AHA by having a carbonyl group in the position of a carboxyl group. 42 It is a potent peeling agent with a pka of 2.39 and is soluble in water and ethanol. Pyruvic acid is physiologically converted to lactic acid and is used in concentrations of 40 70%. 28,42 It causes ablation of the stratum corneum and dermo-epidermal separation resulting in decreased epidermal thickness. 42 Over a long term it induces increased collagen, elastic fibre and glycoprotein deposition in the papillary dermis. 28 Pyruvic acid causes intense pain on application and its vapour is pungent and irritating. 28,44 Resorcinol Resorcinol is a phenol derivative. It has a pka of 9.32 and is soluble in water, ether and alcohol. 28,30 Resorcinol stimulates prostaglandin E2 formation and disrupts the hydrogen bonds of keratin. 30,45 This accounts for its keratolytic and bactericidal properties. Resorcinol is used at concentrations of 10 50% for chemical peeling and induces a frosting pattern. 28 It is used in the treatment of acne, acne scars, hidradenitis suppurativa nodules and melasma. 45 Adverse effects associated with resorcinol include allergic and irritant contact dermatitis, myxoedema and ochronosis from prolonged use, and methaemoglobinaemia. 44 TCA MEDIUM-DEPTH PEELING AGENTS TCA is a tricholorinated carbonic acid that exists in a hygroscopic and deliquescent crystal form. 28,30,43 It has a pka of 0.26 and is hydrophilic. 42 TCA precipitates epidermal proteins and causes destruction of the upper dermis. 30 It is dissolved w/v in distilled water to create the desired concentration for chemical peeling. 30 This solution is clear and colourless, and is best stored in an amber-coloured glass bottle for up to 6 months. TCA cannot be neutralised and has not been associated with allergic reactions or systemic toxicity. 28,40 It may be used alone or as part of a combination peel. Common pairings include solid carbon dioxide and TCA 35% (Brody peel), Jessner solution and TCA 35% (Monheit peel), and glycolic acid 70% and TCA 35% (Coleman peel). An important concept relevant to TCA is that of frosting. Frosting refers to the whitening of the skin due to protein coagulation (Fig. 2). 46 It is an unreliable but widely used guide of keratocoagulation and peel depth. 33 Superficial TCA peeling is performed with concentrations of 10 30%, which induces a level 1 frosting pattern (Table 3). 28 Medium-depth peeling is performed with TCA 35 50%, which causes a level 2 pattern. Higher TCA concentrations (>50%) cause a level 3 frosting pattern and should be used with caution due to the risk they present of post-inflammatory hyperpigmentation and scarring. 28,40 Several cosmetic procedures use high-concentration TCA in a localised manner. Atrophic acne and varicella scars may be treated with 70 100% TCA via a targeted toothpick application as part of the chemical reconstruction of skin scars technique. 47,48 Xanthelasma palpebrarum may also be treated with a focal application of 50 100% TCA. 49,50 Phenol DEEP-PEELING AGENTS Phenol (C 6 H 5 OH, also known as carbolic acid or hydroxybenzene) is an aromatic hydrocarbon with a pka of 9.99. 43 It is derived from coal tar and in its pure state exists as a crystal. 1,46,51 For chemical peeling, liquefied phenol USP, a solution containing phenol 88% and water 12%, is used. 1,40,51 The physical effects of phenol vary according to its concentration and the surface area to which it is applied. 6 At concentrations of above 80% phenol causes rapid and irreversible denaturation and coagulation of epidermal keratin and proteins. 40 This action results in the formation of a barrier that prevents the penetration of the peeling agent into the deep dermis. 6 Conversely, when phenol is diluted to 50% it functions as a keratolytic agent. 6 It disrupts sulphur bridges and allows phenol to penetrate further into the dermis, causing greater destruction and systemic absorption. 6 Figure 2 Frosting pattern on upper lip of a middle-aged woman treated with a local combination peel of alpha hydroxy acid 70% and trichloroacetic acid 40%.

Chemical peels 175 Table 3 Lipophilic phenol is rapidly absorbed via the skin into the systemic circulation. 51 Serious adverse effects include cardiac arrhythmias, renal failure and hepatotoxicity, making it a potentially dangerous agent in inexperienced hands. 40 Baker Gordon formula The Baker Gordon formula contains 88% phenol (USP; 3 ml), croton oil (3 guttae), hexachlorophene (Septisol) soap (Vestal Laboratories, St Louis, MO, USA; 8 guttae), and distilled water (2 ml). 6 Croton oil is a vesicant derived from the seed of the Croton tiglium plant that promotes deeper penetration and absorption of phenol. 6,46,51 Hexachlorophene is a liquid soap that increases surface tension, acts as an emulsifier and retards phenol penetration. 6,51 It balances the irritant and macerative effects of phenol and croton oil. 6,46 Variants Frosting reaction patterns Frosting intensity Depth of peel Clinical findings I Superficial Blotchy/speckled white frost; mild erythema II Medium Even white frost; background erythema III Deep Solid white frost; no background erythema Several other formulas have been described for deep chemical peeling. They consist of phenol of varying concentrations together with other ingredients such as croton oil, water, distilled water, hexachlorophene, olive oil and glycerine. Examples of these peels include Litton, Brown, and Venner-Kellson formulas. GENERAL PRINCIPLES Chemical peel consultation History The pre-procedure consultation should begin with an assessment of the patient s motivation for chemical peeling as well as their expectations of treatment. Any history of cardiac, hepatic or renal disease, diabetes mellitus, immunosuppression or nutritional deficiency should be elicited, as patients with these comorbidities are at increased risk of toxicity, delayed wound healing and infection. 5,7,51,52 Previous resurfacing procedures, Herpes simplex infection, postinflammatory hyperpigmentation, photosensitivity and abnormal (hypertrophic and keloid) scarring should be noted, as these factors increase the risk of post-peeling complications. 53 Having undergone prior radiation and X-ray therapy also requires evaluation as these treatments may reduce the density of adnexal structures, delaying re-epithelisation and increasing the risk of scarring with dermal peels. 2 5 Likewise, recent facial surgery with significant undermining, large flap repairs and rhytidectomy should be identified as these procedures may alter cutaneous blood supply, impairing wound healing. Finally, concomitant dermatological conditions that may worsen with chemical peeling should be noted. These include eczema, psoriasis, vitiligo, rosacea and seborrhoeic dermatitis. 3,5,31,53 All current and past medications require review. The use of isotretinoin in the previous 6 12 months increases the risk of delayed re-epithelialisation and scarring with medium-depth and deep chemical peels. 3,4,30 Similarly, the use of photosensitising drugs, hormonal agents and oral contraceptives increases the risk of post-peel hyperpigmentation. 5,52,55 The occupation, lifestyle and hobbies of the patient require exploration. The amount of UV light exposure should be quantified and photoprotection maximised. 4,52 The patient s smoking status should also be determined and cessation for at least 1 week before and 6 months after each procedure is recommended. 4,52 Lastly, women of childbearing potential should be asked about possible pregnancy and where relevant, their breastfeeding status clarified. Examination The physical examination should begin with assessment of skin colour using the Fitzpatrick skin phototype scale. 2,5 Skin colour is used to predict the pigmentary response to chemical peeling and to guide the selection of patients for test-spot testing. 2,5 The degree of photoageing should also be assessed with a standardised tool such as the Glogau classification. 2 The patient is then examined for the presence of intact pilosebaceous units, sebaceous gland activity, skin thickness and health, laxity of periorbital skin, pre-existing inflammation and hypertrophic or keloid scarring. 2,4,5 Photographic documentation Baseline photography is highly recommended. Photographs may be used to guide peel selection and for before-and-after comparisons. The use of polarised light to highlight pigment and capillaries is adjunctive to standard lighting. Informed consent A detailed consent discussion should be undertaken by the treating clinician and appropriately documented in the medical record. This process may be facilitated by photographs and videos of the peeling procedure, the provision of written information and the use of a dedicated consent form. 56 Patient selection Superficial chemical peels are suitable for all Fitzpatrick skin phototypes. 30 The ideal candidate for medium-depth and deep chemical peeling has a composite of blue eyes,

176 AA O Connor et al. fair complexion and female sex. 6,7,57 Dry skin, superficial fine rhytides and minimal gross redundancy are other desirable characteristics. 7,27 Care should be taken when treating patients with Fitzpatrick III VI phototypes as they are at greater risk of pigmentary dyschromias and scarring. 6,38 Chemical peeling in male patients should also proceed with a degree of caution. 58 Men have thicker, coarser and more oleaginous skin, making the penetration of the peeling agent less predictable. 6 Moreover, they are less likely to employ cosmetic camouflage techniques during the post-treatment phase. 6,58 Test-spot testing The role of test-spot testing in chemical peeling remains controversial and thus is infrequently performed. 59 Testspot testing involves the application of the medium-depth or deep-peeling agent to a small area of skin in an inconspicuous area or at the edge of the treatment field. 6,60 Common areas for test-spot testing include the lateral temple, anterior hairline and pre-auricular region. 60 The advantages of test-spot testing include the more accurate predication of peel efficacy, healing time, pigmentary response and post-peel complications. 59,60 It also facilitates the proper selection of candidates, alleviates their anxiety and discourages impulsivity. 60 The disadvantages of this technique include a delay of treatment, misrepresentative results and the persistence of the test-spot until the definitive procedure takes place. 59,60 Pre-peel care Priming is a term that encompasses all pretreatment and preparation activities that are performed on the skin prior to chemical peeling. 5,42 The goal of these activities is to thin the stratum corneum, enhance the penetration of the active agent and accelerate healing. 5,42 These activities enhance patient compliance, detect intolerances and reduce the risk of complications such as post-inflammatory hyperpigmentation and scarring. 5,28,42 They also allow the clinician to identify patients who are non-adherent with treatment regimens, making them less suitable candidates for chemical peeling. 28 Pretreatment Pretreatment of the skin should begin at least 2 4 weeks before the chemical peel and ceased 3 5 days prior. 5,31,42 Patients should be instructed to limit their UV exposure and apply a broad-spectrum sunscreen with a sun protection factor of 50+ that blocks both UVA and UVB each morning. 5,42 Photoprotective activities are important as they prevent sunburn, diminish tanning and reduce melanocyte activity. 52 Sunscreen should ideally be instituted 3 months prior to the procedure and continued indefinitely thereafter. Tretinoin 0.025 0.05% cream should be applied nocte for a minimum of 2 weeks (preferabley longer to avoid pre-peel irritant dermatitis) before the chemical peel. 29,40,52 Tretinoin (all-trans retinoic acid) causes decreased epidermal adhesion resulting in thinning of the stratum corneum. 40 This enables the peeling agent to penetrate the skin more rapidly and deeply. 40 Tretinoin also enhances epithelial differentiation and accelerates epithelial proliferation, hastening re-epithelialisation. 42 It may be restarted after the procedure once healing is complete. 40 Hydroquinone 2 4% cream is a phenolic compound used to treat dyschromias 29 and in the post-peel setting it reduces the risk of post-inflammatory hyperpigmentation. 29,40 In post-inflammatory hyperpigmentation-susceptible individuals hydroquinone is inititated at least 2 weeks before a chemical peel and re-introduced 1 2 weeks postpeel. Hydroquinone reversibly inhibits the enzyme tyrosinase and selectively damages melanocytes and melanosomes via the formation of free radicals. 61 Adverse effects of this bleaching agent include allergic and irritant contact dermatitis as well as ochronosis. 40 Other topical agents that may be used in the pretreatment phase include glycolic acid 5 10%, salicyclic acid 5 10%, kojic acid 1 4%, azelaic acid and topical corticosteroids. Patients should be instructed to avoid waxing, electrolysis and dermabrasion for a minimum of 3 4 weeks prior to chemical peeling. 52 Individuals with a history of recurrent herpes simplex virus infection should be commenced on systemic antiviral treatment prior to medium-depth and deep chemical peeling. 5 Preparation The day prior to peeling the patient should wash their skin with non-residue soap and refrain from using moisturisers and make-up. On the day of the procedure the patient should wash their skin with a non-residue cleanser and wear no jewellery or contact lenses. 43 Prior to chemical peeling the skin should be degreased with acetone, triclosan or isopropyl alcohol to remove residual cosmetics, oils, loose keratin, and other debris. 1,28,30,54 PEELING TECHNIQUE Location, personnel and equipment Chemical peeling should be undertaken in a dedicated procedural room with appropriate lighting, adequate ventilation and access to resuscitation equipment. 6 An assistant should be present to position the patient, manage equipment and to blot tears from the medial canthal regions to prevent the backtracking of the peel agent into the eye. Under no circumstances should the patient be left alone during the procedure. At a site separate to the patient, the peeling agent should be checked and poured into a small, clearly labelled glass receptacle or prepared according to the product specification. The clinician should remove any crystals that have formed in the solution as these may increase the concentration of the solution that is applied. The peeling agent should be securely stored and never passed across the patient in case of inadvertent spillage. Neutralising agents and eye

Chemical peels 177 irrigation solutions such as water, saline or glycerine must be readily available. Local occupational health and safety practices and infection control guidelines must be followed. This includes wearing gloves throughout the procedure. Patient The patient undergoing facial chemical peeling should be positioned supine with their head elevated on a pillow at 45 and a towel placed around their neck. Their eyes should remain closed for the procedure and appropriate eye shielding provided where appropriate. A surgical cap or hair band is used to keep the hair off the treatment site. Petrolatum or zinc oxide paste may be applied to the lateral canthi, nasal alar grooves, nasolabial folds, lips and oral commissures to prevent pooling of the peeling agent in these areas. Pain control and anxiety management is an important aspect of patient care. This may be achieved by physical agents (e.g., cool packs and fans), oral agents (e.g., paracetamol, non-steroidal anti-inflammatory agents and anxiolytics), regional nerve blocks and general anaesthesia. 43 Superficial peels generally do not require anaesthesia, whereas phenol peeling often requires sedation, regional or general anaesthesia. 6 spatula is used to apply gels. Chemical peeling should start on areas of thicker skin. The forehead, cheeks, nose and chin are treated first, followed by the perioral and periorbital skin (Fig. 3). The peeling agent should be applied in an upward direction with firm even strokes and extended beyond the vermillion border and into the oral commissures. 4,7 Care should be taken to avoid overlapping brush strokes and skipping areas. A feathering technique should be employed at the edge of the treatment field to avoid sharp demarcation lines. 4 In areas of deep wrinkling the clinician should stretch the skin to prevent pooling of the peeling agent. Post-procedure care Good post-peel care ensures prompt recovery of the skin and prevents unwanted complications. The patients should be given written information on what to expect over the ensuing days and instructions on how they should care for their skin. They should be instructed to wash their face with a non-soap cleanser and to avoid rubbing, scrubbing, scratching or picking their skin. A bland emollient should be applied regularly to the skin until peeling is complete. Indications and contraindications Indications and contraindications for chemical peels are listed in Table 4. Application The application technique varies according to the peeling agent used. Liquid products may be applied with a brush, cotton tip applicator or cotton or gauze swab. A wooden Table 4 Indications and contraindications for chemical peels Indications Aesthetic conditions Dilated pores, photoageing, superficial fine rhytides, superficial scars Epidermal proliferations and tumour Actinic keratoses, dermatosis papulosa nigra, milia, seborrhoeic keratoses, sebaceous hyperplasia, warts Inflammatory dermatoses Acne cosmetica, acne excoriee, acne vulgaris, comedonal acne, pseudofolliculitis barbae Pigmentary disorders Ephelides, lentigines, melasma, post inflammatory pigmentation Contraindications Absolute Active infection (bacterial, viral or fungal), history of allergy to peeling ingredient, isotretinoin therapy within the previous 6 months (for medium-depth and deep chemical peels), open wounds, pregnancy Relative Inflammatory dermatosis (e.g. rosacea, atopic dermatitis, and psoriasis), radiation exposure, recent facial rejuvenation surgery Figure 3 Aesthetic units of the face.

178 AA O Connor et al. If crusting develops a topical antibacterial agent may be prescribed. Make-up may be applied after re-epithelisation has taken place. Sun avoidance and daily application of sunscreen should also be encouraged. COMPLICATIONS Chemical peels are a relatively safe procedure provided they are performed under the supervision of an experienced clinician. Appropriate patient and peel selection, counselling, priming and aftercare minimises the risk of complications. 53 Despite such measures, adverse effects can occur following chemical peeling and vary according to peel depth. They are divided into minor and major subgroups. Minor Minor complications may occur within minutes to hours of the procedure. These include irritation, burning, erythema, pruritus, oedema and blistering. 11,52,62 Minor complications also occur in a delayed fashion appearing over days to weeks. These include the development of acneiform eruptions, infection (bacterial, fungal and viral), persistent erythema, demarcation lines and milia. Pigmentary changes (hyperpigmentation and hypopigmentation), textural changes, scarring (atrophic, hypertrophic and keloid) and the increased pigmentation of naevi may also occur. 2,53 Major Although they are rare, major local and systemic complications of chemical peeling include allergic reactions, laryngeal oedema, toxic shock syndrome, cardiotoxicity, salicylism, acute kidney injury, lower lid ectropion, corneal damage, significant scarring and dyspigmentation. 63 COMBINATION TECHNIQUES Chemical peels are often combined with other cosmetic procedures for cutaneous resurfacing. This synergistic approach to facial rejuvenation provides a fast, cost-effective and less invasive alternative to surgery. 64 Microdermabrasion Chemical peeling may be combined with microdermabrasion for the treatment of photoageing, moderately deep rhytides and acne scars. Microdermabrasion involves the mechanical exfoliation of skin by the application of microcrystals. 65 A specialised closed-circuit device containing a vacuum propels aluminium oxide, sodium bicarbonate or salt crystals of varying velocities against the skin. 65 This action abrades the stratum corneum allowing for increased penetration of the chemical peel. Microneedling Microneedling (also known as percutaneous collagen induction or collagen induction therapy) involves the penetration of the stratum corneum into the papillary dermis with needles. This results in the formation of microchannels and a demarcation current that stimulates the release of growth factors that are involved in neocollagenesis and neoangioenesis. It may be combined with glycolic acid to manage acne scars. 66 Botulinum toxin-a injections (BTX-A) BTX-A injections may be combined with chemical peeling techniques for facial rejuvenation. The relaxation of the facial muscles responsible for dynamic rhytides allows for superior collagen remodelling and cutaneous healing. 64 This combination technique carries a theoretical risk of excessive toxin dispersion in the setting of marked inflammation. The timing of BTX-A injections should thus be carefully considered when using aggressive peels. In the authors experience, BTX-A injections may be performed at the same time as a superficial peel, but are best performed a week before medium-depth and deep chemical peels. Dermal fillers Soft tissue augmentation with hyaluronic acid may also be combined with superficial chemical peeling. However, non-hyaluronic fillers in conjunction with concurrent medium or deep chemical peels carries a theoretical risk of biofilm formation and should be discouraged. Ablative laser resurfacing Individuals with mixed photoageing such as combination complexion and volume issues may benefit from the sequential application of ablative laser and medium-depth chemical peeling in one session to different areas. For example, TCA 35% is applied to the skin first, followed by fractionated carbon dioxide laser to treat periorbital and perioral rhytides. 42 CURRENT PRACTICE Over a 4-week period (19 November to 18 December 2016) we conducted an online survey to understand better the chemical peeling practices of Australian Dermatologists. A 17-question electronic survey constructed using SurveyMonkey (San Mateo, CA, USA) was emailed to the 52 dermatologists listed on the Australasian College of Dermatologists website as performing chemical peels (Table S1). The response rate was 60% (31/52), of which 30/31 respondents performed chemical peels. Of these respondents 60% were male, 77% were aged between 35 and 54 years and 43% had 10 19 years of clinical practice as dermatologists. Most respondents (40%) in our survey prescribed chemical peels on a weekly basis. The most common depth of chemical peel performed was very superficial (73%). In contrast, only three (10%) respondents reported performing deep chemical peels. Boutique or pamper peels were

Chemical peels 179 performed by 27% of respondents. Dermatology nurses (73%), dermatologists (47%) and dermal therapists (27%) most commonly performed the chemical peel. In total, 77% of our respondents reported combining chemical peels with other treatments. These included BTX-A injections (52%), dermal fillers (39%) and radiofrequency procedures (22%). Nine (39%) respondents reported combining chemical peels with treatments other than those listed in the survey, which included AHA, topical retinoids, oral acne therapy, intense pulse light, cryotherapy, daylight photodynamic therapy and shave excision. Only 20% of respondents reported performing a test-spot test as part of their clinical practice. Reasons cited included routine practice, darker skin type, patient ethnicity (e.g., Asian), previous adverse outcome (e.g., postinflammatory hyperpigmentation or dyspigmentation) or prior to the performance of a deep chemical peel. The most common age range of patients on whom chemical peeling was performed on was 30 41 years (33%). Altogether 70% respondents reported performing chemical peels on both men and women, 30% on women alone and none exclusively on men. Fitzpatrick phototype I and II (93 and 97%, respectively) were the most common skin types selected for chemical peeling. Common areas for chemical peeling included the face (100%), chest (40%) and neck (37%). The most common indications for chemical peeling were photoageing (87%), comedonal acne (67%), lentigines (60%) and melasma (60%). Two respondents listed xanthelasma and acne rosacea as other indications for chemical peeling. Adverse outcomes with chemical peeling were reported by 27 (90%) respondents (Table 5). The most commonly encountered adverse effects included hyperpigmentation (67%), persistent erythema (52%), oedema (37%) and acne or folliculitis (37%). Five (19%) respondents indicated other adverse effects. These included a lack of efficacy, desquamation and death (one respondent). Despite a follow-up email sent to all respondents, further details of the latter serious adverse event could not be elucidated. RECENT ADVANCES AND FUTURE DIRECTIONS Boutique or pamper peels (e.g., Valeant Pharmaceuticals, Irvine, CA; Rationale, Rationale Skincare Melbourne, Victoria, Australia; Aspect Dr, Advanced Skin Technology, Melbourne, Victoria, Australia) have become increasing popular in recent years. These products consist of conventional peeling agents (e.g., AHA, beta hydroxy acid and TCA) in combination with various botanical extracts, vitamins and other adjunctive ingredients, which may be incorporated in a proprietary topical delivery vehicle. While there is no significant evidence favouring boutique peels over conventional peels, superior marketing, cobranding with cosmeceutical ranges and a greater emphasis on enhancing the patient s experience have increased the presence of boutique peels in the chemical peel sphere. Table 5 Adverse effects of chemical peels (from a survey of Australian dermatologists) There is also an increasing trend for superficial peels to be used as maintenance therapy after intense pulsed light and fractional resurfacing procedures. This offers patients the opportunity to engage with trained nurses and therapists to develop a maintenance skin care programme with at-home cosmeceuticals in conjunction with periodic inclinic peels. CONCLUSION Chemical peels remain a rapid, safe and cost-effective technique for cutaneous rejuvenation, particularly in our ageing, photodamaged population. 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Chemical peels 181 63. Perkins SW. Complications of chemical face peeling: prevention and management. Facial Plast. Surg. 1995; 11: 39 46. 64. Landau M. Combination of chemical peelings with botulinum toxin injections and dermal fillers. J. Cosmet. Dermatol. 2006; 5: 121 6. 65. Kisner AM. Microdermabrasion with chemical peel. Aesthet. Surg. J. 2001; 21: 191 3. 66. Sharad J. Combination of microneedling and glycolic acid peels for the treatment of acne scars in dark skin. J. Cosmet. Dermatol. 2011; 10: 317 23. Supporting Information Additional Supporting Information may be found online in Supporting Information: Table S1. Results of the chemical peel survey (n=31).