Chemical peels have been used for hundreds of years by many different cultures as a means of exfoliating the skin. Some chemical acids are natural agents that have been chemically changed to an acidic pH. Other chemical acids contain molecules that are naturally found in the skin. With an acidic pH, histological changes occur in the epidermis and dermis. In cosmetic dermatology, different types of hydroxy acids, dicarboxylic acids, enzymes, or chemical compounds can be used to improve skin conditions.
With cutaneous resurfacing, there are various options depending on the condition of the skin and desired clinical outcomes. There are three main types of peeling agents commonly used to resurface the skin: keratolytic agents, proteolytic agents, and keratocoagulant agents. Keratolytic agents work by breaking apart the bonds that hold skin cells together or by dissolving cellular glue. Keratolytic agents include hydroxy acids, such as glycolic, lactic, or salicylic acids. Proteolytic agents are enzymes that dissolve dead skin cells. Keratocoagulant agents, such as trichloroacetic acid (TCA), work by coagulating skin proteins. TCA is applied in layers and has the ability to penetrate deep into the dermis.

EXFOLIATING THE EPIDERMIS
Hydroxy acids and enzymes are commonly found in superficial peels. Hydroxy acids are keratolytic agents that dissolve the cellular bonds that hold dead keratinized cells together found in the stratum corneum. There is a difference in hydroxy acids and their properties and knowing the skin condition will help to determine which type of hydroxy acid is optimal. Hydroxy acids can be either water- or oil-soluble and can be used synergistically to help improve skin conditions. Hydroxy acids have the ability to create histological changes in the epidermis and dermis and can encourage sebum secretion, eliminate comedones, and can be used to enhance treatment for a variety of conditions including acne, rosacea, melasma, dyschromias, photodamage, and actinic keratoses. Synergistically, hydroxy acids can be combined with proteolytic or keratocoagulant agents or could be alternated for optimal results.
Enzymes are proteolytic agents that include natural ingredients, such as papaya, pineapple, and pumpkin, and are ideal for treating compromised or sensitive skin conditions. Enzymes work by dissolving cellular tissue found in the top layer of the epidermis and can be combined with keratolytic agents. At the epidermal level, superficial exfoliation with enzymes remove accumulated dead skin cells and new cells are stimulated to regenerate.

EXFOLIATING THE DERMIS
Medium depth and deep peels commonly contain keratocoagulant agents such as TCA, which works by coagulating skin proteins. Keratocoagulant agents have the ability to penetrate into the papillary or reticular dermis. Medium depth chemical exfoliation stimulates the synthesis of collagen and glycosaminoglycans. Medium depth exfoliation is commonly applied in layers and restructures the skin by stimulating the liberation of cytokines, which are the key molecules in cellular control. Layered chemical resurfacing can be used to treat moderate to severe conditions such as dyschromia, multiple solar keratoses, superficial scars, and pigmentary disorders.

DETERMINING CHEMICAL PEEL SOLUTION
With chemical solutions and application, there are numerous factors to consider that can affect clinical outcomes. Factors such as pressure, concentration, peeling agent, conditioning the skin, priming the skin, and pH solution should be considered prior to treatment. Other considerations, like altering the pH (known as buffering), free acid value, and contraindications, should be considered, as well.

pH
An acid must be reactive to make histological changes in the skin and the pH level can have an effect on the strength of a chemical peel solution. Some acid solutions are buffered which is when the natural pH level of an ingredient is altered. This process can either increase or decrease a pH level by utilizing other chemicals and can greatly affect the strength of a solution. The strength of pH is determined by factors of 10. With acids, each number in a pH value is 10 times stronger than the higher number or level. In summary, an acid with a 1.0 pH is 10 times stronger than an acid with a pH of 2.0.

Determining Free Acid Value
Chemical peel solutions are compounds that contain other substances, such as water or alcohol. The free acid value of a product means that the product only contains the acid agent itself and does not contain any other substances. With chemical compounding, a 30 percent hydroxy acid compound mixed with water or other agents will not be as strong as a 30 percent hydroxy acid without added substances. A hydroxy acid without any added substances is considered a free acid and has full strength or full value.

With chemical peels, it is advised to have a current health history and signed consent form prior to each procedure. Factors such as medications, stress, immunity, and ethnicity could affect the choice of peeling agent, strength, and pH.
With rejuvenation therapy, factors such as medications, skin health, and ethnicity could affect the choice of exfoliation therapy and clinical outcomes, and should be considered prior to cosmetic procedures.
Post-procedure, wearing a broad-spectrum physical sunblock ingredient, such as zinc oxide, will protect the new cells that were stimulated during the rejuvenation process. Zinc oxide is a broad-spectrum physical sunblock ingredient and is also anti-inflammatory and assists in tissue repair.

Linda Gulla is a NSPEP physician endorsed master aesthetician and is a published writer in cosmetic dermatology whose material has been reviewed and endorsed by dermatologist Dr. Eric Schweiger, as well as the renowned Dr. Abdala Kalil. As a published writer, Gulla’s expertise can be found in the Milady Advanced Esthetics 2nd Edition. Gulla has shared her expertise with family physicians and dermatologists as an adjunct instructor with the National Procedures Institute, where her material was reviewed by over seven medical review boards and was ACCME accredited. Gulla is founder of the Institute of Advanced Aesthetics and Health Sciences and is recognized as an approved provider with the NCEA COA. Her online self-study program can be found at iaahs.com. Professionals can obtain additional reference material that covers this entire series on Chemical Resurfacing in Dermatology and Advanced Layered Peels by visiting her website at iaahs.com.