Monday, 25 February 2019 02:57

Chemical Exfoliation: Understanding Hydroxy Acids, pH, and More

Written by   Linda Gulla

With cutaneous resurfacing there are various options depending on the condition of the skin and desired clinical outcomes. There are three types of exfoliating agents commonly used to resurface the skin. Keratolytic agents, keratocoagulant agents, and proteolytic agents. Keratolytic agents, such as hydroxy acids, 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 acid. Keratocoagulant agents work by coagulating skin proteins. Keratocoagulant agents include trichloroacetic acid (TCA), which is applied in layers and can penetrate deep into the dermis. Proteolytic agents include enzymes that dissolve cellular tissue and are a gentle and effective method to rejuvenate the skin. Enzymes such as papaya, pineapple, and pumpkin are ideal to exfoliate sensitive skin types. Individual skin type and condition of the skin will help to determine which exfoliating agent would be optimal. Synergistically, exfoliating agents can be alternated for optimal results.

Skin condition will determine which type of hydroxy acid is optimal. Hydroxy acids can be used synergistically to treat skin conditions and are commonly used together as part of a skin care regimen. Alpha hydroxy acids are water and oil soluble, beta hydroxy acids are oil soluble, lipohydroxy acids are oil soluble, and polyhydroxy acids are water soluble.

At the dermal layer, medium depth and deep peels may contain keratocoagulant agents that coagulate proteins in the skin and can penetrate the papillary or reticular dermis. Medium depth exfoliation is commonly applied in layers and restructures the skin by stimulating collagen renewal and the liberation of cytokines, which are the key molecules in cellular control. Layered chemical resurfacing can be used to treat moderate to severe skin conditions.

With chemical exfoliation and application there are numerous factors to consider that can affect clinical outcomes. All factors should be considered prior to treatment. These include:

  • application (pressure)
  • concentration (the percentage)
  • degree of acid neutralization
  • peeling agent (keratolytic, proteolytic, or keratocoagulant)
  • priming of the skin
  • skin preparation
  • solution pH (level of acid)

With chemical exfoliation, there are numerous factors that need to be considered prior to treatment and when determining peel solutions. Factors such as pH, buffering, and free acid value can determine the strength of a chemical peel solution.

The pH of a solution measures the strength of an acid or base and is measured by dipping litmus into a solution such as water or other substances. The pH scale ranges from zero to 14. If a solution has a pH less than 7, it is considered an acid.  If a solution has a pH above 7 (alkaline), it is a base. A neutral solution has a pH of 7.

An acid must be reactive to make histological changes in the skin and pH must be considered when determining the strength of a chemical peel 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 (level). In summary, an acid with a 1.0 pH is 10 times stronger than an acid with a pH of 2.0. An acid solution must have a pH of 4.0 or less to be able to penetrate the skin and make histological change. There is less irritation to the skin when using pH levels of 3.25 to 3.50.

Buffering 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. With some buffered acid substances, the reaction is slower and the coagulation is less than it would be if the acid peel was unbuffered. With buffering, raising the natural pH of an acidic substance will cause less irritation to the skin. Buffered acid ingredients can also be altered to be lower than their natural pH and be a stronger acidic substance. With a lower pH, buffered acid substances can be a more aggressive and effective form of therapy and can cause irritation to skin.

Chemical acid solutions can be 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.

Prepping the skin prior to chemical peel application will help to improve penetration into the skin. Degreasing the skin with salicylic acid (two percent) or with an acetone scrub will assist the chemical agent into the skin.

Herbal peels use natural herbs and plant extracts to gently exfoliate and regenerate the skin. Herbal peels may contain vitamins, enzymes, and plant hormones which are released into the skin and rejuvenates the skin from the inside out. Herbal peels can vary from a light exfoliation to a deeper rejuvenation of the epidermis and can be combined with other skin rejuvenation modalities.

Linda Gulla 2014Linda 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   

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