Skin Care Including Chemical Peeling

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Chapter 2 Skin Care Including Chemical Peeling

Zoe Diana Draelos

Skin is the defining boundary of our personal space, a self-renewing organ, the first line of defense against systemic infection, and an indicator to others of our chronologic age. It is a barrier that weathers with advancing age and the insults of ultraviolet (UV) radiation to become wrinkled, discolored, and uneven. Skin care includes cleansing, moisturizing, and photoprotection, while chemical peeling is a method for improving the appearance and function of aging skin.

Summary

1. Chemical peeling is the controlled removal of the stratum corneum, epidermis, and/or superficial dermis to improve skin texture and pigmentation.
2. Superficial chemical peeling with hydrophilic glycolic acid or lipophilic salicylic acid is intended to produce mild exfoliation of the stratum corneum.
3. Medium-depth chemical peeling with trichloroacetic acid preceded by a superficial chemical peel is useful in improving facial dyspigmentation.
4. Deep chemical peeling with phenol is useful in improving superficial facial rhytids, but inevitably produces skin lightening.
5. Chemical peel is contraindicated in patients who have been treated with systemic tretinoin within the previous 6 months and as a treatment of keloids.
6. The skin barrier can be visualized as a brick wall consisting of the protein-rich corneocytes functioning as the bricks held in place by intercellular lipids as the mortar.
7. Cleansers are designed to remove environmental dirt, sebum, bacteria, and fungal organisms from the face while leaving the intercellular lipids and stratum corneum barrier intact. Modern cleansers contain synthetic detergents (syndets), such as sodium cocoyl isethionate and sodium laureth sulfate, which maintain skin hygiene, but prevent damage to the intercellular lipids.
8. Moisturizers decrease transepidermal water loss, creating an environmental optimal for barrier repair. They create an occlusive barrier to evaporation (petrolatum, dimethicone, mineral oil) or functioning as a humectant to attract water from the dermis to the viable epidermis and stratum corneum (glycerin, propylene glycol, sorbitol).
9. Estrogen replacement therapy and oral contraceptives predispose the patient to hyperpigmentation following chemical peel.
10. Sunscreens can be added to moisturizers to prevent UVB- and UVA-induced photodamage and photocarcinogenesis.

Introduction

Skin is the defining boundary of our personal space, a self-renewing organ, the first line of defense against systemic infection, and an indicator to others of our chronologic age. It is a barrier that weathers with advancing age and the insults of ultraviolet (UV) radiation to become wrinkled, discolored, and uneven. Skin care includes cleansing, moisturizing, and photoprotection, while chemical peeling is a method for improving the appearance and function of aging skin.

The skin is composed of three layers: the stratum corneum, epidermis, and dermis.

The stratum corneum forms the skin barrier and is composed of two distinct anatomic units:

• protein rich cells (corneocytes);
• skin lipids that hold the corneocytes together (Fig. 2.1).
image

Fig. 2.1 Stratum corneum. The stratum corneum is visually modeled as a brick wall with the bricks representing the corneocytes and the mortar representing the intercellular lipids.

Structural damage to the corneocytes or to the lipids results in a defective barrier. With the aid of an electron microscope, it is possible to see the covalently bound lipid layer between the corneocytes forming an organized watertight seal over the body (Fig. 2.2).

image

Fig. 2.2 Intercellular lipids. The intercellular lipids that surround the corneocytes provide waterproof characteristics to the skin barrier.

Barrier damage occurs when:

• the intercellular lipids are removed, typically by the chemical insult of soaps;
• the corneocytes are physically removed, such as through aggressive scrubbing or the use of chemical peels.

The health of the skin is therefore ultimately dependent on the non-living stratum corneum. The underlying viable epidermis and dermis form the cellular renewable layers of the skin, accounting for its strength and distensible characteristics.

The most important role of the stratum corneum is to modulate the water content of the skin, which should be approximately 30%. Too much water creates maceration and too little water decreases the elastic properties of the skin and creates skin surface wrinkles of dehydration.

Equilibrium between the external climate and internal environment of the body occurs at about 70% humidity; however, the average humidity of a conditioned environment is 20–30%. Therefore, there is a constant net loss of water from the skin to the air (i.e. transepidermal water loss). If this water loss becomes excessive, the skin recognizes that a barrier defect has occurred, resulting in a rapid burst in the synthesis of intercellular lipids (ceramides, sterols, and fatty acids).

Deliberate wounding of the skin, such as the insult induced by chemical peeling, results in a profound, but controlled, damage to the skin structures, requiring the proper selection of skin care products to optimize the cosmetic result.

Indications

Fair complected patients:

• dyspigmentation
• poor skin texture

Relative contraindications

• Patients with dark skin (Fitzpatrick types IV and higher)
• History of consumption of oral retinoids within the past year
• Radiated skin.

Contraindications

• Hypersensitivity to chemical peels
• Keloid formation within 6 months after cessation of oral retinoids
• Evidence of poor healing.

Skin peeling is a controlled removal and renewal of the various layers of the skin, depending on the depth of the wound:

• superficial peels wound the stratum corneum and possibly the upper layers of the epidermis;
• medium-depth peels wound the stratum corneum, epidermis, and superficial dermis;
• deep chemical peels wound the stratum corneum, epidermis, and mid-dermis.

The depth of the peel is controlled by the strength of the acid applied to the skin surface and the length of time for which the acid is left in contact with the skin.

Chemical peels are a carefully controlled wounding of the skin and are designed to improve cosmetic appearance.

Any part of the body can be subjected to a chemical peel, but the face produces the most dramatic and reliable results. This is because the facial skin is thin and it heals with minimal scarring. The face is the only body site where a deep chemical peel is performed.

Superficial chemical peels produce little effect on any area other than the face where they are used to produce a mild exfoliation improving skin texture. This improved skin texture is appreciated by the patient as increased facial shine (sometimes referred to as radiance) and smoother facial cosmetic application.

Medium-depth chemical peels may be performed on the entire body, but are most frequently used on the neck, chest, and arms. Typically, higher concentration acids are used on the face with a reduced concentration applied to any other body area.

Chemical peels produce the best results in fair complected individuals (Fitzpatrick type I and II) with predominantly pigmentary photodamage. Darker skin types (Fitzpatrick type III and higher) are more challenging to treat with chemical peeling because the inflammation induced by the superficial or medium-depth peel may result in unsightly post-procedure hyperpigmentation. Darker skin types also more frequently exhibit hypertrophic scarring and keloid formation, predisposing to an undesirable outcome.

Deep chemical peels are never performed on darker skinned individuals because the acid may damage the melanocytes, resulting in permanent hypo- or depigmentation, unless hypopigmentation is part of the aesthetic goal.

A chemical peel can be performed for a variety of indications:

• superficial chemical peels can be used to enhance exfoliation, improve skin texture, and minimize comedonal acne;
• superficial peels damage the skin barrier and may be used to enhance the penetration of topical medications, such as hydroquinone skin lightening cream or tretinoin, and
• a superficial chemical peel is the first step in performing a medium-depth peel, allowing deeper penetration of the acid into the skin;
• medium-depth peels are used to improve defects in skin pigmentation (such as lentigenes and melasma), and fine lines around the eyes and upper cheeks;

The best indication for chemical peeling is to improve facial pigmentation.

A medium-depth peel will not improve deeper rhytids around the mouth and folds on the face, such as the nasolabial and melolabial folds. It is not possible to successfully improve facial folds with any type of chemical peel, but deeper rhytids around the mouth and on the lateral cheeks can be improved with a deep chemical peel, possibly combined with a facelift procedure or the use of injectable fillers.

In my opinion, the best indication for chemical peeling is in the improvement of facial pigmentation. The precise ability to control the depth of the peel by proper acid selection yields excellent pigment removal without further dyspigmentation or scarring. Although laser resurfacing is sometimes used for pigmentation improvement, the laser does not afford the control of chemical peeling. Chemical peeling is an art combining visual assessment of the peel depth produced by the different types and strengths of acid left on the skin for varying intervals. This allows clinicians to adapt the chemical peel to the varying degrees of pigmentation in the treated area.

Preoperative History and Considerations

A detailed history must be obtained prior to a chemical peeling procedure to ensure an optimal outcome and result longevity.

Individuals who have been treated with systemic retinoids should not undergo a chemical peeling procedure for at least 6 months to 1 year, depending on the depth of the chemical peel desired. This is because systemic retinoids such as isotretinoin reduce the activity of sebaceous glands and thereby increase susceptibility to hypertrophic scarring, which can be disastrous in the case of a chemical peel where the entire face is wounded.

A history of oral hormone supplementation is also important. Estrogen replacement therapy and oral contraceptives predispose the patient to facial hyperpigmentation. In some individuals, dyspigmentation may rapidly return following a facial peel if exogenous estrogen is consumed. Discontinuation of the estrogen for at least 3–6 months prior to the procedure and after the procedure is advantageous, but not always feasible. Women who are not able to discontinue their estrogen should be advised that the pigmentation may return and counseled on the proper use of photoprotection.

It is also worth inquiring about the patient’s skin care regimen. Patients who are using prescription topical retinoids, such as tretinoin, adapalene, or tazarotene, will experience much deeper and more rapid penetration of the acid into the skin. Although retinoids are used prior to medium and deep chemical peels to enhance penetration, they may produce a much deeper peel than expected or desired in patients wishing only a superficial chemical peel.

Patients may also be undergoing microdermabrasion, spa-administered chemical peels, or other aesthetician procedures that damage the skin barrier, enhancing acid penetration and yielding unexpected results.

Operative Approach

The peeling procedure for superficial, medium, and deep peels is somewhat similar, each deeper peel building on a more superficial skin wounding (Table 2.1).

Table 2.1 Chemical peel technique comparisons.

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Superficial peels

Superficial peels usually consist of either a glycolic or salicylic acid solution applied to the face in three coats. Glycolic acid superficial peels are water-soluble (hydrophilic) in contrast to salicylic acid peels, which are oil soluble (lipophilic).

Glycolic acid peels

Glycolic acid peels in concentrations of 10% or less may be applied by unsupervised aestheticians in a spa setting, but concentrations of 20% or higher should be applied by a physician or in a carefully supervised setting.

Glycolic acid peels are formulated by diluting a 70% stock saturated solution of glycolic acid in concentrations of 20, 30, 40, 50, and 60% with water. The most commonly used glycolic acid peels are:

• 20 and 30% for gentle skin exfoliation;
• 70% for mild dyspigmentation.

The peels can be administered in a weekly series with gradual 10% increases in strength from 20 to 70% to achieve a cumulative effect and enhanced improvement in photoaging. Glycolic acid peels are water soluble and therefore only peel a skin surface devoid of oil.

Salicylic acid peels

Salicylic acid peels are able to peel the skin surface as well as in the oily milieu of the pore. Salicylic acid peels are therefore preferred for patients wishing comedolysis as part of acne treatment or for patients wishing to remove retained hairs and other debris from within the pore.

Salicylic acid peels are formulated from salicylic acid powder, which is dissolved in either benzyl alcohol or ethanol in concentrations ranging from 10 to 50%. I prefer benzyl alcohol as solvent because it is less pungent.

Glycolic acid peels are water soluble and only peel a skin surface devoid of oil, whereas salicylic acid peels are lipophilic and peel not only the skin surface but also in the oily milieu of the pore.

10–20% concentrations of salicylic acid peels are solutions, whereas 30–50% peels are shake lotions and the salicylic acid must be resuspended prior to application.

Salicylic acid is unique in that it does not penetrate into the dermis making it an ideal superficial peel for patients with sensitive skin, rosacea, or other inflammatory skin diseases.

Peeling procedure

A superficial peel can be the desired treatment endpoint or it may be followed by a medium-depth peel, which is actually a two-step peeling procedure with a stratum corneum wounding procedure followed by a deep epidermal or superficial dermal wounding procedure.

Superficial peel

• The first step in peeling is to degrease the face and remove all skin care products and cosmetics. If the skin is not clean, the superficial peel will not penetrate and no skin improvement will be perceived. I prefer to use a triclosan solution to clean the face with aggressive gauze scrubbing, but any soap-based cleanser can be used.
• Following cleansing, the skin should be thoroughly dried and the patient placed on the exam table with a bedside fan blowing a gentle breeze across the face.
• Next, a rectal swab should be used to apply the 2 mL of superficial peel solution poured into a small shot glass (Fig. 2.3A).
• The solution should be applied in three coats to the entire face. I begin with broad strokes across the forehead, moving down to both cheeks, then to the chin, upper lip, and lastly across the nose (Fig. 2.3B).
• It is important to avoid applying the solution to the corners of the eye, nose, and mouth. Any junction between cornified skin and mucosa should be avoided because these areas tend to peel more deeply and a painful erosion may result.
• At all times, an eye should be kept on the skin of the patient to determine the degree of barrier damage. Superficial peels should only wound the stratum corneum and uppermost epidermis. The depth of the peel can be assessed by asking the patient about their level of discomfort. I typically ask the patient to rate the stinging and burning on a scale of 1–10 with 10 indicating extreme pain. The application of the peel solution should cease when the patient complains of discomfort at the 4–5 level, even if three coats have not been applied.
• It is also important to watch for reddening and whitening of the face. Reddening of the face indicates early wounding and vasodilation whereas whitening (also known as frosting) indicates deeper wounding and protein coagulation. The more confluent the whitening of the skin, the deeper the peel (Fig. 2.3C). Very minimal scattered whitening is all that should be achieved with a superficial peel. The peel is immediately neutralized with cool water on disposable washcloths wiped across the face until the stinging and burning has resolved. Neutralization is extremely important in glycolic acid peels because the acid will continue to wound the skin until removed. However, salicylic acid peels are self-neutralizing because the acid crystallizes on the skin surface. Thorough water rinsing is soothing to the skin surface. I usually completely rinse the skin three times and follow this by an application of a bland occlusive moisturizer, such as Cetaphil cream (Galderma, Ft Worth, TX). Further skin care considerations are discussed in the Skin care section.
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Fig. 2.3 Superficial peeling procedure. A, 1–3 mL of the peel solution is decanted into a small glass crucible for application. B, A rectal swab stroked over the face is used to apply the peel solution to the skin surface. C, The confluence of the skin whitening is an indication of the depth of the peel.

Medium-depth peel

• It is most important to remove all grease from the skin surface when a superficial peel is preparation for a medium-depth peel. I prefer to use acetone on a gauze vigorously rubbed across the face following triclosan cleansing. This removes all traces of oil from the skin surface ensuring even uptake of all the peel solutions in both oily and dry facial areas.
• There is tremendous variability in the medium-depth prepeel. Some clinicians prefer glycolic acid, whereas others use a carbon dioxide slush peel or a mechanical microdermabrasion peel. My preference is to use a combination prepeel with both lipophilic and hydrophilic substances to prepare the skin surface and the pores for the medium-depth peel procedure. This prepeel solution is known as Jessner’s peel and is a combination of lactic acid, resorcinol, salicylic acid, and ethanol. It is applied in one to three coats to the skin surface with a rectal swab until early whitening of the skin is achieved.
• Once whitening has occurred with the prepeel, 25–35% trichloroacetic acid is quickly applied evenly to the entire face with a lightly moistened rectal swab. The strength of acid selected depends on the depth of the desired peel, which is determined by the degree and confluence of facial frosting (Fig. 2.4A).
• At this point, the fan should be blowing briskly across the patient’s face and ice cold water compresses applied as soon at the desired amount of frosting has occurred (Fig. 2.4B).
• After the burning has subsided, the face should be examined for any skip areas that might need to be touched up.
• It is not necessary to neutralize either the Jessner’s prepeel or the trichloroacetic peel because they are both self-neutralizing.
• A heavy layer of petroleum jelly is then applied over the entire face, followed by petroleum impregnated gauze, Telfa, and netting, if desired. The face should be rinsed with warm tap water at least twice daily and covered with petroleum jelly until re-epithelialization is well underway by postprocedure day 4. At this time, cosmetics can be worn and the patient is socially acceptable.
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Fig. 2.4 Medium-depth peel. A, Facial appearance immediately after a mild trichloroacetic acid peel. B, Ice-cold disposable towels are placed over the face to decrease the warmth, stinging, and burning associated with facial peeling.

Deep chemical peels

Deep chemical peels:

• are not commonly performed because most patients who desire the results of a deep peel prefer to undergo a laser resurfacing procedure;
• are performed with phenol, which is cardiotoxic, requiring intra-operative monitoring, and produces permanent pigment lightening.

Optimizing outcomes

• Initiate nightly application of a retinoid 3 weeks prior to chemical peel.
• Remove all sebum and cosmetics from the face prior to initiating the peel.
• Apply the peel solution quickly and evenly to the entire face – if areas of the face are skipped, reapplication is required, which prolongs the procedure time and pain.
• Do not drip the peel solution into the eyes or outside the desired peel skin area.
• Some patients may prefer to take a sedative prior to the procedure, though reassuring conversation, careful fan placement, and quick application of ice cold towels can provide adequate pain relief for the short duration of the procedure.

Optimizing a medium-depth peel result

• Ensure even penetration of the acid over the entire face, especially on the oily areas such as the nose – this is achieved by having the patient use a retinoid nightly for 3 weeks prior to the peeling procedure. My preferred retinoid is 0.025% tretinoin cream, but other strengths of tretinoin (0.05 or 1%), adapalene, or tazarotene cream may be used. The retinoid should be discontinued for 1 month after the peel to allow healing to occur and then restarted to maintain the cutaneous peel effect for as long as possible. (Retinoids can also be used with superficial peels, but the strength of the superficial peel solution may need to be decreased).

Complications and Side Effects

Chemical peeling is a relatively safe procedure, but a few complications should be avoided. Proper patient selection to avoid using the procedure in dark complected patients and those with healing disorders is key to avoiding complications of scarring, hyperpigmentation, and hypopigmentation. In addition, patients who have a history of frequent herpes simplex infections of the peeled body area should be treated with preventive acyclovir, famciclovir, or valacyclovir on the day of the procedure to prevent dissemination of the herpes simplex virus in the wounded area.

Postoperative Care

The amount of postoperative care depends on the degree of the skin wound. Superficial peels require no postoperative care, whereas medium and deep chemical peels require application of petroleum jelly, to prevent undesirable water loss from the wounded skin surface, at least twice daily with warm tap water rinsing of the area for at least 4 days. At day 4, most patients can begin wearing cosmetics and use a foaming face cleanser accompanied by a simple oil-in-water moisturizer (Eucerin cream, Beiersdorf, Germany). It is best to follow up the patient 1 week after a medium or deep peel procedure to ensure that healing is progressing and there are no problems.

If the medium-depth peel is being performed to improve skin dyspigmentation, a hydroquinone-containing bleaching cream is recommended 1 week after the peel. This prevents repigmentation from UV exposure and hormonal influences. The use of a physical sun block, containing zinc oxide or titanium dioxide, may also be helpful to prevent UVA stimulation of the melanocytes.

Skin care

Postpeel skin care is important and includes the use of cleansers and moisturizers.

Skin cleansing is the chemical interaction of surfactant with the skin surface combined with physical rubbing. The physical rubbing and the chemical interaction are equally as important.

Proper skin cleansing removes sebum, apocrine and eccrine secretions, environmental dirt, bacteria, fungal elements, yeast, desquamating keratinocytes, medications, cosmetics, and skin care products while not removing intercellular lipids or damaging the brick and mortar structural organization of the stratum corneum.

Cleansers

There are a variety of skin cleansers,1–3 including soaps, syndets, and combars (Table 2.2), which can be placed on a variety of cleansing implements from the hands to a washcloth to a disposable face cloth.

Table 2.2 Skin cleanser categories and properties.

Type of cleanser (commercial examples) Advantages Disadvantages
Soap Excellent cleansing thorough sebum removal Can dry skin; not recommended for sensitive, healing or diseased skin
Syndet (synthetic detergent)
Combar		 More mild cleansing; recommended post-surgery; may be used for sensitive or diseased skin Not as thorough sebum removal
Good cleansing; commonly combined with triclosan topical antibacterial; good choice for high-risk wound infections or contaminated body areas  

Synthetic detergents (syndets), particularly in the form of a foaming face wash, are the best post-procedure cleansers. Combars are a combination of soap and syndet and are useful post-surgically for the patient who is at risk for cutaneous infection.

True soap is a specific type of cleanser with an alkaline pH of 9–10 created by chemically reacting a fat and an alkali to create a fatty acid salt with detergent properties. Soap efficiently removes both sebum and intercellular lipids, making it an excellent general skin cleanser, but a poor choice following any type of surgical procedure resulting in a damaged barrier.

The need for good hygiene in a compromised barrier situation has led to the development of synthetic detergents, known as syndets (Fig. 2.5). The most popular syndet cleansers contain sodium cocoyl isethionate with a neutral pH of 5.5–7. This more neutral pH removes fewer intercellular lipids, preventing further barrier damage during cleansing. These products, particularly in the form of a foaming face wash, are the best post-procedure cleansers.

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Fig. 2.5 Cleansers. A variety of cleansers are illustrated, from left to right, a syndet bar soap, a foaming facial cleanser, and a lipid free cleanser.

The final category of traditional cleansers is combars, which combine soap and syndet cleansers in the same product with a pH of 7–9. Combars remove more sebum than a syndet cleanser, but less than a soap cleanser. Most deodorant cleansers fall into this category and contain triclosan as a topical antibacterial. Combars are useful post-surgically for the patient who is at risk for cutaneous infection.

Moisturizers

Moisturizers (Fig. 2.6)4–7 are applied to the skin following cleansing in the post-surgical patient to minimize transepidermal water loss, so creating an environment that is optimal for skin healing.

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Fig. 2.6 Moisturizers. A variety of moisturizers are illustrated, from left to right, a lotion, a cream, and an ointment.

The three categories of substances that can be combined to enhance the water content of the skin are occlusives, humectants, and hydrocolloids:

• occlusives are oily substances such as petrolatum, lanolin, mineral oil, vegetable oils, dimethicone, and cetyl alcohol that retard transepidermal water loss by placing an oil slick over the skin surface;
• humectants are substances such as propylene glycol, hyaluronic acid, glycerin, sorbitol, gelatin, urea, sodium lactate, vitamins and proteins, that attract water to the skin, not from the environment, unless the ambient humidity is 70%, but from the inner layers of the skin – humectants draw water from the viable dermis into the viable epidermis and then from the nonviable epidermis into the stratum corneum;
• hydrocolloids are physically large substances, such as peptides and colloidal oatmeal, that cover the skin, therefore retarding transepidermal water loss.

A quality moisturizer will combine ingredients from all three categories to provide multiple mechanisms of moisturizing the skin.

A commonly marketed moisturizer formulation combines petrolatum (the most effective moisturizing ingredient presently known) with dimethicone to minimize greasiness and effectively retard 99% of the transepidermal water loss. The addition of glycerin to hold water in the skin with a peptide to create an artificial barrier complete the formulation. Incorporating vitamins, such as vitamin C or vitamin E, or botanicals (such as aloe, green tea, or soy) add distinction among products in the marketplace.

The biggest challenge in the delivery of anti-aging substances to the skin is the stratum corneum. An intact stratum corneum is key to the skin barrier and a necessary part of post-procedure healing, but impedes the penetration of many substances into the skin. This extremely important function means that the stratum corneum prevents infection and the entry of toxic foreign substances and allergens into the body. However, the barrier also prevents most large molecular weight proteins and botanicals from entering the skin and functioning as modulators of collagen production or topical antioxidants.

Probably one of the most effective moisturizer additives is sunscreen, which has the ability to both prevent and reverse photoaging.

Sunscreens

Sunscreens8–19 are an important part of post-surgical skin care. Inflammation resulting from a face peel or other skin wounding procedure can cause hyperpigmentation, especially in the presence of UVA radiation, which stimulates melanin production by melanocytes.

Photoprotective mechanisms may be endogenous (Table 2.3) or externally applied (Table 2.4).

Table 2.3 Natural cutaneous UV protective mechanisms.

Cutaneous structure Sun protective mechanism
Compact horny layer Absorbs and scatters UV
Keratinocyte melanin
1. UV absorbing filter
2. Free radical scavenger
3. Dissipates UV as heat
4. Undergoes oxidation in 300–360 nm range to produce immediate pigment darkening

Carotenoid pigments
1. Membrane stabilizers
2. Quench oxygen radicals

Urocanic acid Oxidized to stabilize UV-induced oxygen radicals Superoxide dismutase
1. Oxygen radical scavenger
2. Protects cell membrane from lipoprotein damage

Epidermal DNA excision repair Repairs UV-induced DNA damage

Table 2.4 Sunscreen ingredient comparison.

image

Sunscreen ingredients can be classified into two major categories.

• Chemical ingredients undergo a chemical transformation, known as resonance delocalization, to absorb UV radiation and transform it to heat. This reaction occurs within the phenol ring, which contains an electron-releasing group in the ortho and/or para position. This chemical reaction is irreversible, rendering the sunscreen inactive once it has absorbed the UV radiation.
• Physical sunscreens, in contrast, are usually ground particulates that reflect or scatter UV radiation, absorbing relatively little of the energy. For this reason they have longer activity on the skin surface.

Sunscreen ingredients can be divided into the following three groups:

• UVA (320–360 nm) absorbers, such as oxybenzone, avobenzone, menthyl anthranilate;
• UVB (290–320 nm) absorbers, such as PABA derivatives, salicylates, cinnamates;
• UVB/UVA blocks that reflect or scatter UVA and UVB, such as titanium dioxide, zinc oxide.

Most modern sunscreen formulations are a blend of two to three different substances carefully selected to compliment one another and enhance product performance (Fig. 2.7). However, raising the SPF above 30 only confers an incremental increase in photoprotection (Fig. 2.8).

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Fig. 2.7 Sunscreen protection. Sunscreens are combined to provide the broadest coverage of absorption spectra yielding optimal photoprotection in the UVB and UVA range.

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Fig. 2.8 SPF and photoprotection. The relationship between SPF and the degree of photoprotection is not linear. This means there is very little increase in photoprotection beyond an SPF of 30.

UVA sunscreen ingredients

Proper UVA photoprotection is important because it is this spectrum of radiation that results in photoaging, skin pigmentation, and photocarcinogenesis.

Oxybenzone is a widely used weak UVA (it absorbs at 320 nm) absorber commonly used as a secondary sunscreen to increase the broad-spectrum protection of the formulation. It is an oil-soluble ingredient that can add to the sticky feel of a sunscreen if used in too high a concentration. It has been used in combination with 2–6-diethylhexylnaphthalate to stabilize avobenzone (also known as Parsol 1789), which is highly photounstable with 36% of the avobenzone destroyed shortly after sun exposure.

Oxybenzone may also be combined with menthyl anthranilate (also known as meradimate) to extend UVA photoprotection with a peak absorption at 336 nm. Meradimate is commonly used as a secondary UVA photoprotectant because it is a sticky oil and can decrease sunscreen aesthetics.

UVB sunscreen ingredients

The sunscreen ingredients that contribute the sun protection factor rating (known as the SPF), provide protection against UVB exposure, which contributes to sunburn and photocarcinogenesis.

The salicylates, such as octisalate and homosalate, are important UVB photoprotectants, with internal hydrogen bonding providing for maximal UVB absorption at 300–310 nm. Approximately 56% of sunscreens currently available use the salicylates as a secondary sunscreen active because of their minimal allergenicity.

86% of products with an SPF rating of 15 or higher contain octyl methoxycinnamate (also known as octinoxate), which has maximal absorption at 305 nm. Octinoxate has excellent photostability with only 4.5% degradation after UVB exposure and is commonly used in sunscreen-containing moisturizers and facial foundations.

Physical UVA/UVB absorbers

The physical UVA/UVB absorbers are titanium dioxide and zinc oxide.

• Titanium dioxide is usually micronized to contain particles of many sizes to provide optimal UV scattering abilities. It leaves a white film on the skin and is used mainly for beachwear products.
• Zinc oxide is usually available in a microfine form (i.e. it contains small particles of one size), making it appropriate for day wear in persons of all skin colors. Zinc oxide-based sunscreens provide the most complete post-procedure photoprotection, especially after completion of a chemical peel.

Conclusion

Chemical peeling is a versatile method of improving skin texture, pigmentation, and fine lines, especially on the face, but also on other body areas. It improves skin appearance by encouraging exfoliation while removing dyspigmented skin. It is an acquired art that requires no special equipment and can be performed for a relatively small investment.

Following a superficial, medium, or deep chemical peel, proper skin care is important to ensure optimal healing and longevity of the result and involves the use of mild cleansers to prevent barrier damage and moisturizers to enhance the water holding capacity of the skin. Sunscreens that provide both UVB and UVA photoprotection must also be applied to prevent unnecessary photodamage.

The combination of proper skin care and a well-executed cosmetic procedure will optimize skin appearance.

References

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