The word “peel” literally means “remove the outer layer”, or “refine”. In effect, this is a process of exfoliating horned cells to improve the visual appearance and the overall condition of skin.
A special place among various peels is occupied by chemical peel. It consistAs not in mechanical exfoliation which does not exclude skin damage, but in dissipation of dead cells in the superficial skin layer upon contact with peel components. As a rule, organic acids are the active components of chemical peel.
A chemical peel entails the application of exfoliating chemicals to the skin, resulting in a destruction of the epidermal and dermal structures. Depending on a variety of influencing factors, the effects of the peels can reach varying depths and alter or injure different structures. Regenerative mechanisms are set in motion in the damaged skin layers, the aim being to cause an objective improvement in the structure, and importantly, the appearance of the skin.
This part deals with the basic dermatological knowledge relating to the hypothetical mechanisms of action of chemical peels. Descriptions of the structure and function of the skin are accompanied by an explanation of the basic principles and mechanisms of epidermal barrier regeneration and dermal wound healing.
Types of chemical peels according to affection depth:
- Superficial peel is effective in the range of several horned epidermis layers. It is the most sparing kind of chemical peel. After the procedure, patients can follow their usual lifestyles. Generally, it is recommended for young problem-prone skin. The effect is not lasting and it is advised to repeat the procedures.
- Medium-depth peel affects the whole horny layer of epidermis up to basal layer. After these procedures, patients need to stay at home for a week because of hyperemia and small- or large-flaked desquamation. This peel is performed to solve particular problems and to fight the age-related skin changes. The effect is long-lasting, and it is recommended to repeat the procedures only in a year.
- Deep chemical peel consists in epidermis rejection with affecting basal layer. This procedure is fairly responsible and performed under anesthesia because it presents a chemical face burn with the following epidermis regeneration. It is directed at the removal of deep wrinkles and scars and is performed at hospital. The effect is rather long-lasting (up to several years), but the procedure can be carried out only once. The rehabilitation period lasts for about 5 months.
Principal purposes of chemical peel:
- Exfoliation (sloughing off) of horned epidermis which results in proliferation (generation) of basal layer cells. This means renewal of the whole skin cover.
- Removal of skin imperfections and problem solving as a result of exfoliation and particular properties of acids.
- Activation of protective and regenerating skin functions due to the stress effect of acids.
What is chemical peel needed for:
Often, chemical peel is chosen to correct cosmetic skin defects of face and other body parts. Consequently, patients are offered:
- Improvement of skin’s visual appearance: skin becomes smoother, tenderer, with an even complexion;
- Disappearance of pigment spots, post acne, scars and stretch marks;
- Normalized pH and secretion of sebaceous glands;
- Dry skin;
- Rejuvenation of face skin due to smoothing of wrinkles, increased skin firmness and plasticity thanks to improved synthesis of collagen.
Indications for chemical peel:
- Problem-prone skin (post acne, blackheads, comedones);
- Hyper pigmentation;
- Low-toned, not elastic, loose skin;
- Age-related skin changes;
- Photo aging (skin affected by excessive UV radiation);
- Scars and stretch marks;
- Oily skin with enlarged pores;
- Thickening of the horny layer which results in skin roughness;
- Dull complexion;
- As a preparatory stage before deeper and more serious cosmetological procedures;
Contraindications for chemical peel:
- Any chronic diseases in their aggravation stage;
- Cold-related diseases;
- Pregnancy and breast-feeding;
- Predisposition towards hypertrophic or keloid scars;
- Necessity for radiotherapy;
- Fresh suntan;
- Recent (performed less than 8 weeks ago) traumatic procedures (deep cleansing, mesotherapy, laser resurfacing);
- Mental illnesses;
- Separate peel component idiosyncrasy;
- Intake of immunosuppressants, retinoids, photosensitizing medications;
- Pronounced couperosis;
- Oncology diseases;
- IV–VI skin photo types according to Fitzpatrick scale for medium to deep peels;
- Skin diseases (eczema, allergic dermatosis, atopic dermatitis, psoriasis, etc.) in their aggravation stage;
- Infectious skin diseases (viral, bacterial, fungal);
- Damage of skin cover, traumas in the peel application area;
- Slow dermal wound healing;
- Diabetes and hypertensive disease.
- Multiple nevi;
- Hyper sensitivity of skin;
- Age under 18 years;
Mechanism of acid peel action:
- Damage of epidermis (chemical burn).
- In response, skin cells start intense synthesis of inflammation mediators, signalling molecules, enzyme increase factors.
- Mitotic activity of basal cells is increased (cells actively regenerate).
- New vessels are created and the generation of fibroblasts is intensified. As a consequence, new collagen, elastin, glycosaminoglycans and enzymes are synthesized.
- Derma is thickened and tightened; all skin layers are moisturized.
- Correct pH gradient of the skin is restored and skin renewal enzymes activated.
How is skin cover structured?
Knowledge of skin anatomy and physiology is necessary for understanding the mechanism of any cosmetological procedures.
Skin is not only a human body covering. This is a full-fledged organ with a range of particular functions and complicated structure. The overall skin mass amounts to approximately 5% of body weight. Human skin surface is covered with about 5 million hairs. On the average, every square centimetre of skin contains 100 pores and 200 receptors.
Complete renewal of young skin takes 28 days. With advancing age, this process gets slower every year, and the horny layer thickens and becomes uneven. The thickness of the horny layer can also increase under the influence of ultraviolet rays.
Human skin has regular pH 3.5-5.6. If it is noticeably shifted, skin problems, such as rashes and irritation, may appear. Acidic pH is typical of dry skin, alkaline pH more of oily skin. There can also be mixed-type skin, when skin type differs in separate areas. Thus, it is necessary to know your skin type in order to select correct cosmetic solutions.
Under physiological conditions, the density of the horny layer of the epidermis results from the quality of its keratinous matter (keratin filaments, amorphous substances), and the formation of an intercellular diffusion barrier (lipid cement). Both the construction of an intact skin barrier in the stratum conjonctum and the desquamation in the stratum disjunctum are associated with enzyme activity. Among other factors that influence it, this activity is pH-dependent. The pH optimum of the epidermal lipid hydrolases (B-glucocerebrosidase and acid sphingomyelinase) is about 5.0 whereas that of the phospholipases A1 and A2 and the serine proteases is above 7.0. All these enzymes have significant functions for the epidermal barrier and their Physiological activity is regulated by the epidermal pH gradient and acidic membrane compartments at the stratum granulosum-stratum corneum interface. Influences on the stratum corneum pH gradients alter these enzyme activities, and this can then impair the structure and function of the entire epidermis. In particular, alkaline compounds found in topical skin care products (detergents), which enhance the skin surface pH have a negative effect on the differentiation of the keratinocytes by neutralising the acid surface pH, and also affect the integrity of the barrier.
With superficial chemical peels in acid formulation, one aim is to achieve non-physiological shifts in the epidermal pH gradient. Therefore, using solutions with pH Specifically, this allows for the stimulation of enzymes that synthesise the barrier lipids and control desquamation.
Skin structure consists of three principal layers: epidermis (upper skin layer), derma, or skin itself, and subcutaneous fat (hypoderm). Each has its own layers, appendages and elements.
The upper layer of skin – epidermis has the utmost importance in cosmetology. Its structure is multilayered. In epidermis, melanin is produced. This pigment determines skin color and its intensity.
Unlike aqueous solutions, oil-soluble substances freely penetrate epidermis because cell membranes contain numerous fats and these substances “dissolve” in them. Epidermis has no blood vessels and is nourished by diffusion of tissue fluid from the underlying derma layer.
Basal layer is the base of epidermis. It is a blastogenic layer of intensively multiplying cells which substitute the ones dying and sloughing off every day.
Above the basal layer, there is a spinous layer in which cells have spine-like appendages. Right here, in the intercellular space, lymph circulates to ensure nourishment and metabolism in epidermis cells.
Above the spinous layer, granular, clear and horny (uppermost) epidermis layers are arranged sequentially.
Cells of epidermis:
- Keratinocytes are cells of spinous, basal and granular layers that move permanently. They are created from splitting blastogenic cells of the basal layer located between epidermis and derma. They mature and shift from lower to upper layers (from spinous to granular layer) while cumulating keratin (a very solid protein).
- Corneocytes are created in the end of keratinocytes lifespan. They are cells without nucleus and basic organelles, a kind of a “bag” full of keratin. Corneocytes are dead cells, flat scales forming the horny layer. They carry out the barrier function of epidermis.Corneocytes move further up, come to the skin surface, slough off and are substituted by new ones. Corneocyte renewal takes about three weeks. Corneocytes are mutually bound by a special substance consisting of a double layer of particular lipids – ceramides. Molecules of ceramides have hydrophilic “heads” (water-retaining fragments) and lipophilic “tails” (oil-retaining fragments).
- Melanocytes are cells of the basal layer that are located in the malpighian layer of epithelium and generate melanin. This pigment carries out the protective function by guarding the human organism from infrared and partially from ultraviolet radiation. The degree of melanin concentration determines the color of skin. The state of basal layer in some cases determines the formation of pigment spots.
- Langerhans cells carry out the protective function against foreign bodies and microbes.
- Merkel cells are tactile cells in the basal layer of epidermis. They are responsible for skin sensitivity. Most Merkel cells are located in the skin of fingertips, nose tip and erotogenic zones.Under basal layer there is derma, or skin itself. It consists of the papillary and reticular layers. Papillary layer is bound to epidermis. The papillary pattern on palms and feet represents nothing else but dermal papillae that can be seen through epidermis. Lower, there is the reticular layer containing sebaceous and perspiratory glands, hair follicles, nerve endings (skin receptors), as well as collagen and yellow fibres. Skin elasticity and solidity depend directly on the yellow fibres and the amount of collagen in derma.
Subcutaneous fat layer is located under the reticular layer of derma and carries out the amortization and calefacient functions.
Mechanism of acid action on skin:
Chemical peels comprise organic acids. Superficial peel involves fruit acids, medium-depth – trichloracetic (TCA), deep peel – phenol and trichloracetic acid in higher concentration.
When applied on skin, according to its concentration and exposure time, acid dissolves horned cells of upper epidermis layers and sometimes the whole epidermis up to basal layer.
In other words, by applying a peel solution, specialists achieve a controlled chemical burn of face skin. Unlike a traumatic burn, in this case the depth of affection is strictly controlled by the cosmetician to solve those particular problems of the patients that have brought them to a cosmetology clinic.
Fruit and some other acids have an exfoliating effect achieved due to loosened cohesion of corneocytes in the horny layer. In response to intensified flaking, cells of the basal layer start active splitting (mitosis).
Moreover, acids have a moisturizing effect due to accelerated renewal of epidermis because on the surface of keratinocytes, there is a complex of hygroscopic molecules, or NMF – natural moisturizing factor. This factor is mostly contained in young cells.
Chemical acids have a stimulating effect on skin fibroblasts and therefore promote the synthesis of glycosaminoglycans and collagen.
The stress theory also explains the intensified synthesis of intercellular substance in derma. Protective systems of skin are activated in response to stress. Skin is toned, the reparative regeneration of its cells is amplified, and the synthesis of vital molecules is accelerated.
As a result, epidermis grows thinner and derma thickens. Skin surface becomes more elastic and firm, minor wrinkles get smoothed.
Acids normalize the lipid balance, cleanse the canals of sebaceous glands and therefore decrease skin oiliness and prevent acne and comedones.
Exfoliation of horned epidermis cells results in skin whitening. Moreover, some acids affect the synthesis of melanin and also ensure lightening of skin.
The basal keratinocytes react to the damage of cellular and intercellular structures by increasing their rate of mitosis and synthesis, with concormintant stimulation of desquamation. This regularises the differentiation cycles of the keratinocytes from the basal layer upwards. Keratin and lipids involved in the construction of a semi-permeable horny layer are once again synthesised in sufficient amounts, and cell-to-cell contacts are restored. This results in a compact, smooth horny layer with an intact barrier function.
Superficial peels induce epidermal regeneration. This can remedy epidermal anomalies. Un wanted side-effects are very rarely observed with lighter skin types. However, the risk of hyperpigmentation needs to be kept in mind with darker skin types.
Wound healing can be dived into three consecutive phases:
Phase 1: Inflammatory phase ( Phase 2: repair phase (1 to several weeks)
Phase 3: remodelling phase (weeks to several months)
Its duration depends on the extend of the damage that has occurred as well as on individual factors.
Sufficiently extensive damage to the dermal tissue is initially followed by an inflammatory reaction. Inflammatory mediators (cytokines, chemokines, prostaglandins) attract tissue-bound macrophages, leukocytes, and fibroblasts. Dilated vessels enable perivascular infiltration of the tissue. Nerve endings are sensitised, which can lead to a temporary increased sensitivity to pain and irritability of the skin.
During the subsequent repair phase, the damaged tissue in the dermis is broken down with the envolvement of MMPs and macrophages. Re-epithelialisation sets in at the same time. It starts from the epithelium-lined hair follicles. Complete renewal of the skin surface can take from a few days to several weeks, depending on the degree and area of damage.
The remodelling phase of the dermal connective tissue can take several months. The fibroblasts attracted during the inflammatory phase are responsible for the neosynthesis of the components of the extracellular matrix. Following this, collagens and elastins embedded in the water-binding matrix are reassembled into a stable and elastic network of fibres.
Areas with a high density of sebaceous glands, characterised by hair follicles that extend all the way into the subcutaneous tissue, undergo a more rapid, reliable, and complete regeneration compared to areas containing few sebaceous glands. Ethnicity is also of significance to dermal regeneration capacity: fibroblast in darker skin types are large, multinucleate cells. Appropriate stimulation causes overproduction of collagen with minimal breakdown of the extracellular matrix. Thus, Fitzpatrick 5 and 6 skin types have 20% greater probability of developing keloids
following skin injury, compared to lighter Fitzpatryk skin types.
Pigmentation anomalies are due to dysregulated melanocyte activity, and manifest clinically both as a lack (hypopigmentation) and an excess (hyperpigmentation) of melanin. They are often the consequence of chronic inflammatory lesions, caused by unprotected exposure to UV light. Inflammatory mediators stimulate the basal epithelial cells and thus also act on the melanocytes that are located there. The excess melanocyte activity can lead to postinflammatory hyperpigmentation.
Chemistry of peeling:
Which skin layers a peel will reach and how the skin structures are affected depends to a significant extent on the method of application as well as the chemical properties of its active substances. Basic knowledge of the chemistry of the substances used and of the biochemical reactions is therefore essential to fully understand this treatment modality and its indications.
The basics of the entire treatment concept need to be clear: apart from the effects of the peel itself, it is important to appreciate the role of the pre-peel adjunctive topical therapy alongside the immediate pre-peel treatment of the skin.
The cosmetic outcome of a chemical peel primarily depends on the level and depth of the penetration of the peel and the course of the subsequent skin regeneration. How deep a peel can penetrate, i.e. damage incurred, depends on the chemical characteristics of its active substance and the patient´s skin type.
A peel can reach vatious depths; the terms superficial, medium and deep peels are often used to classify the general methods of treatment.
- Superficial peel: the peel only penetrates the epidermal layers.
- Medium peel: the peel penetrated down to the papillary dermis and is able to achieve dermal remodelling.
- Deep peel: the peel penetrates down to the reticular dermis and is ale to achieve extensive, long-lasting dermal remodelling.
Substances with a primarily superficial effect (AHA, pyruvic acid, salicylic acid) have a minimally invasive effect. They are acids that cause a shift in the physiologic pH gradients of the stratum corneum and can also modify proteins. A reduction in cell cohesion and an effect on enzyme activities can explain the exfoliative effect that is clinically apparent following a superficial peel treatment. After a superficial peel the stratum corneum becomes thinner, it also becomes more compact as a result of an efficient regeneration.
The superficial peels can be used to treat skin ageing, actinic keratosis, atypical cells, pigmentation changes.
Supercial peels are categorized from A to D, frost/no frost.
Stages of chemical peels:
- Pre-peel treatment. skin adaptation to the acid and evening out of the upper layer to ensure better penetration of peel solution. It begins 2 weeks before the procedure.
- Peel treatment: receiving the desired result depending on the choice of the active acid. It is performed on protocol. The concentration, pH and exposure time are determined by cosmetician.
- Post-peel treatment: prevention of complications and fixing the result of peel. Homecare solutions are prescribed by the specialist, and patients have to carry out all the instructions. It is also necessary to use all day shield sunscreens with SPF 30 or higher.
Correct pre-peel treatment, peel performed by a qualified specialist and well-selected after-peel treatment decrease the risk of complications significantly.
To ensure that an active substance can penetrate the skin´s layers as desired, the skin surface needs to be degreased and cleansed.
A thorough understanding of the relevance of degreasing is required as well as ensuring that the correct cleansing agent is used prior to the peel depending on the desire effect and the type of peel used.
For water based peels:
- all in one cleanse & peel or micellar water cleanse & peel to remove the make-up and impurities.
- enzyme powder cleanse & peel to remove dead cells by an enzymatic process and all superficial fats.
- monsoon mist tone & peel that is slightly alkaline (pH 8) to allow the stratum corneum to swell up and get well hydrated before to apply the peel.
The result is gentle degreasing of the skin’s surface and, at a small extent, breakdown of the uppermost cell layers. The subsequently applied peel is better able to penetrate the horny layer pre-treated this way and can act more uniformly.
For alcoholic peels:
- all in one cleanse & peel or micellar water cleanse & peel to remove the make-up and impurities.
- enzyme powder cleanse & peel or degreasing solution to deeply degrease the skin and remove dead cells.
The intensity of the cleansing that is needed depends on the chemical properties of the peeling solution, the quality of the patient´s skin, and the goal of the treatment.
Pre and post peel formulas
Peels must always be seen in the context of adjunctive topical pre and post-peel therapy. The skin treatment pre and post chemical peeling (PHA activator & Ice cream repair) is carried out by the patient using preparations specially designed to support the regenerative effect of the treatment with regard to the patient’s individual requirements. Depending on the depth of the peel and the condition of the skin, various active substances are used for topical treatment, to be applied by the patient for longer periods of time before and after the peel.
This is not common cosmeceutical homecare practice, but a treatment employing formulas developed specifically for a time period before and after a given rejuvenating medical intervention.
Goals of pre and post-peel formulas
The intended effect of adjunctive topical therapy for chemical peels is based on accelerated regeneration (EGF, FGF, Hyaluronic acid, unirepair, peptides) on the one hand and on prevention of hyperpigmentation of the other (hexyl-resorcinol, vitamin A, peptides, enzymes, acids).
The aims of the topical therapy that accompanies repeated superficial peels is to stimulate the proliferation rate and to modify cell differentiation, thus potentiating the aesthetic effects of minimally invasive peels in the context of a long term treatment.
PHA activator contains low concentration of PHA acids, when used before, after, and between treatments, it impairs optimal pH of epidermis to activate enzymes and favour those of others.
This stimulates desquamation and restoration of the epidermis.
Exfoliating and keratolytic substances, such as PHA, AHA, enzymes and/or retinoids, encourage the transport of bleaching agents into the basal layer.
The intends clinical effect may be associated with reduced cell cohesion and increased ablation, with a simultaneous increase in the rate of the basal cell layer. This accelerates restoration of the integrity of the epidermal barrier and underpins the long-term effects of superficial peels through the daily application of appropriate topical products.
For patient with Fitzpatrick skin type III or higher, the topical therapy should also include depigmentation agents.
For medium and deep peels, in addition another key goal is to prevent areas of post-inflammatory hyperpigmentation. (upper lip and cheeks)
AHA and PHA:
The use of chemical substances included in the chemical peel and in the adjunctive topical products requires thorough knowledge with regards to the relevant substance classes, their mechanisms of actions, and particularly their solubility.
For superficial AHA or PHA peels, the formulas pH is also of relevance. The solubility of a substance determines how rapidly the skin barrier is penetrated.
Lipophilic substances can readily overcome the lipid barrier in the stratum corneum, even without prior cleansing to remove grease.
AHA and PHA modulate the pH gradient of the epidermis and stimulate exfoliation and epidermal regeneration. They initiate exfoliation of the uppermost horny layers, with effects ranging up to epidermolysis. Studies on human skin confirm that AHAs and PHAs, when used as part of a long-term treatment regime also stimulate synthesis of the epidermal intermediate glycosaminoglycan and collagen in the papillary dermis.
The intensity of the effect is determinate not by the strength of the AHA (its pHs value) but by the pH of the formula, as part of the active substance can be neutralised or buffered.
Effects of AHA & PHA
- Reduction of the pH at the skin surface
- Reduction of corneocyte cohesion
- Restoration of a compact horny layer
- Normalisation of the rete ridges
- Induction of cell proliferation
- Reduction of cellular atypia
- Increase glycosaminoglycans in the epidermis and dermis
AHA and PHA show poor penetration of greasy skin. Thus, particularly meticulous removal of grease is a key prerequisite for successful application of hydrophilic AHA and PHA peels. Since the relevant solutions undergo hardly any absorption through the skin, this also means that the risk of systemic toxicity does not apply.
The use of the carboxy neutraliser is essential to ensure a controlled completion of the peeling process. When AHA and PHA react with sodium bicarbonate, product includes the acid’s salt as well as water and carbon dioxide.
AHA peels are extremely popular due to their sparing effect and practical absence of unpleasant sensations during and after the procedure.
AHA are not producing frosting, they produce an intense erythema and they must be neutralised.
Gluconolactone and lactobionic acid belong to PHA, the next generation of chemical peels. It has an integrated effect on skin and is suitable for patients from different age groups. Thanks to minimal irritating effect, it can be successfully performed even on sensitive skin that is prone to acne.
Polyhydroxy acids penetrate the skin gradually, layer by layer. Due to this fact, their use in peel treatments does not cause strong burning sensation and irritation of skin.