Dr Raul Cetto discusses the mechanisms of action and antiageing benefits of chemical peels
Chemical peeling is the application of a chemical agent of a defined strength, resulting in predictable accelerated exfoliation and skin damage. The release of cytokines and inflammatory mediators following this damage results in thickening of the epidermis, and an increase in dermal volume through deposition of collagen, producing the appearance of rejuvenated skin.1
There are generally three depths of chemical peels: superficial, medium and deep (Figure 1). This article will focus on medium as a discussion on superficial and deep will each warrant an entirely separate article. A medium-depth peel aims to reach the papillary and upper reticular dermis at a depth of approximately 0.45mm. In general terms, medium depth peels use a trichloroacetic acid (TCA) concentration of 35-50%. TCA is an analogue of acetic acid, which was first used by German dermatologist Dr Paul Gerson Unna as a chemical peel – this was documented in 1882.2 Its medical and cosmetic applications continued to be studied throughout the early 20th century and was found to improve the appearance of scars, blemishes and wrinkles in a 50% solution. However, complications such as hyperpigmentation and scarring were high at this concentration. By the 1950s, dermatologists had found several new ingredients to produce mixtures with a lower solution of TCA to reduce the risk and produce a more predictable outcome.3
Several chemical agents are commonly used in medium-depth peels to produce a predictable and controlled exfoliation of the skin –discussed below.
TCA at 35-50% can be used in the treatment of photoageing, particularly actinic keratosis, pigmentation, fine facial rhytides and moderate perioral wrinkles.3 It is not appropriate for the treatment of lax skin or deep rhytides caused by movement of the muscles of facial expression, which would be better treated using a deeper acting peel.5 TCA causes protein to denature leading to keratocoagulation and keratinocyte death. As the skin then re-epithelialises, collagenesis is observed and the previously present abnormal keratinocytes are replaced by healthy new cells.6 The concentration of TCA will also determine the depth of action. For example, a 15-20% TCA concentration will only reach the epidermis, whereas a 45% TCA solution will likely penetrate to the upper reticular dermis.7 Multiple applications should be considered as an alternative to a higher concentration, for example several applications of 20% TCA in six week intervals can produce the same effects as one application at 45%. Higher concentrations or multiples applications of TCA are better tolerated by patients with thick, seborrheic skin, rather than those with smooth thin skin. A period of pre-treatment of the skin with retinoid or hydroquinone (available on prescription only) will improve the penetration, as will proper skin degreasing with an alcohol preparation solution.3 Augmentation of the TCA should also be considered, for example an application of 0.025-0.05% retinoic acid just before TCA application enhances penetration and may provide better results.3 The best results for patients with photoageing are obtained in patients with phototype II, although it is also effective in type III and IV phototype patients. TCA is not systemically absorbed and therefore can be used safely in patients with cardiac, hepatic and renal morbidities.3
Jessner’s solution consists of resorcinol, salicylic acid, lactic acid at 85%, and ethanol at 95%. This was first described by American dermatologist Dr Gary Monheit in 1989.8 Jessner’s solution destroys the epidermal barrier function by breaking the intercellular bridges between keratinocytes allowing a TCA solution (35% is typically used) to better penetrate the epidermis.8 This combination clinically improves the appearance of photoaeing skin, actinic keratoses, and rhytides.8
In 1986, Brody and Hailey reported positive results to treat actinic degeneration, acne scarring, rhytids, and pigmentary aberrations with the application of solid carbon dioxide to ‘ice’ the skin, to enhance the penetration of a 35% TCA solution used.9
The histological specimens studied by Brody and Hailey showed an expanded papillary dermis with neocollagen formation in the sub-epidermal region of the dermis and a mid-reticular dermal band consisting of elastic fibres and collagen. This technique was reported to penetrate to the upper reticular dermis and to be more effective than Jessner’s solution plus 35% TCA in the treatment of acne scarring;9 however, it has been reported that it can destroy melanocytes not confined to the epidermis and therefore result in hypopigmentation, particularly in darker skins.10 It was also noted that the depth of penetration is difficult to control and somewhat unpredictable, yielding variable results and complication, because the depth of action of the solid CO2 is dependent on how hard the operator applied the block to the skin, which is a difficult measure to standardise.9,10
Glycolic acid peels penetrate the skin easily and have anti-inflammatory, keratolytic, and antioxidant effects.11 The glycolic acid peel is applied prior to the TCA. Different concentrations of glycolic acid can be used (30%-70%) to adjust the intensity of the peel.11 Glycolic peels are usually better tolerated by patients compared to Jessner’s solution because it produces less visible exfoliation post procedure.12
Chemical peels can potentially cause several complications, some of which can be treated easily. In general, medium-depth peels produce fewer complications, and with less frequency than deep peels as their penetration is more superficial, so the damage to the skin is more limited. There is no risk of systemic complication when using a medium-depth peel.
Reactive hyperpigmentation can occur after any depth of chemical peel. Usually, lighter complexions have lower risk of hyperpigmentation.1 Priming the skin by using a combination of hydroquinone and retinol creams for several weeks before a medium-depth peel, can reduce the rate of hyperpigmentation.1 Demarcation lines, a harsh line between treated and untreated areas, can be softened if the boundary of the peeling area is hidden under the mandibular line and feathered gradually to the normal skin.13
Hypopigmentation is associated with darker skin types and increased post-peel sun exposure.6
Bacterial and fungal complications in chemical peels are rare.1,14 Patients with positive history of herpes simplex infection should be treated prophylactically with antiviral medications acyclovir or valacyclovir during peeling, until full re-epithelisation is achieved, as all peels can reactivate the virus. Toxic shock syndrome has also been reported after chemical peels, and patients should be warned of the symptoms for this reason.3,14
The contributing factors to the likelihood of post-peel scarring are not well understood yet. However, delayed healing and persistent redness may precede scarring. A topical steroid should be used to treat such scarring as soon as a diagnosis is made, but this may still not prevent unsightly scars from forming.1 The most common location of post-peel scars is in the lower part of the face, and this may be due to more aggressive treatment in this area or possibly due to eating and speaking during the healing process, which moves these tissues.3,7
These are inclusion cysts, which appear as a part of the healing process in up to 20% of patients after chemical peels, usually eight to 16 weeks’ post procedure and can be long-lasting or even permanent. They are more likely to occur in patients who have had a deep peel rather than a medium. If they do not resolve spontaneously, patients can be treated with mild epidermabrasion following re-epithelialisation, gentle extraction or electrodissection.1
Acneiform eruption after chemical peels can appear immediately after re-epithelialisation and is not a rare complication. It can be related to exacerbation of previously existing acne or may be due to overuse of oily preparations on the new skin. Short-term systemic antibiotics, together with discontinuation of any oily products will usually provide relief.1
In the patient’s consultation, various contraindications should be discussed to ascertain whether the patient is a good candidate for the proposed intervention. Absolute contraindications are active and recent bacterial, viral, fungal or herpetic infection, open wounds, a history of the use of medication with photosensitising potential, such as exogenous oestrogen, an oral contraceptive pill or isotretinoin use in the preceding 12 months, inflammatory dermatoses (psoriasis, atopic dermatitis, pemphigus) and facial skin melanoma. In addition, most would call a non-compliant patient an absolute contraindication to this treatment as pre-peel treatments and post-peel sun exposure limitation relies entirely on patient compliance, and non-compliance will likely produce an undesirable outcome. The patient must be motivated enough to adhere to a daily regimen for a few weeks before and after the procedure. If a patient has a history of abnormal scarring, then a medium depth or deep peel would not be recommended. Sun-damaged skin shows epidermal changes, elastosis, and collagen distortion in the mid-reticular dermis and, to eradicate this, a deep peel would be required. More superficial peels, even when performed in repetition, do not reach the affected histological level and therefore have a minimal effect on photodamaged skin.10 Practitioners should advise patients to stop smoking. The dynamic action of puffing can create or worsen perioral rhytides. The smoke can cause squinting, increasing wrinkling around the eyes and nose, and furthermore, the chemicals in the smoke can cause enzymatic reactions that can cause wrinkling around the mouth and eyes.10 Patients should be carefully counselled about the downtime of five to 10 days following a medium depth peel.4 Patients who are overly self-conscious may not be prepared for their aesthetic appearance immediately following the peel. Particularly, patients with unrealistic expectations or suspected body dysmorphic disorder should be excluded from these treatments, and counselled in line with General Medical Council (GMC) guidance on these matters.15 All discussion and steps in the counselling process should ideally be fully documented, as recommended by the GMC.16
The type of peel that will be best for any patient will be dependent on their skin type, their medical history, their cosmetic concerns and their expectations. Thorough counselling is absolutely necessary to ensure that the best possible results are achieved. Patient selection is key with regards to medium depth peel application.