Tuesday, 07 January 2020 23:15

Chemical Reaction: Understanding Chemical Peels for Greater Results

Written by   Sarah Robbins

Chemical peels are acid-based solutions that are intended to create a partial-thickness injury in order to remove the outermost layers of the skin. This results in a wound healing process to increase regeneration in the epidermal tissue. The intention of chemical peels is to improve the appearance of the skin by stimulating new, healthier, and younger looking tissue. It is essential for professionals who offer chemical peels to have an in-depth understanding of acids, peel strength and depth, proper protocols, and more in order to achieve the best results for clients.




Acids are substances derived from natural sources or man-made chemicals used to enhance the exfoliation of the skin. Exfoliating the skin helps keep the skin “active” which, in turn, will keep the skin more youthful. It is similar to exercising the body. Exercising helps the body function better and health is maintained. Exfoliating the skin helps to regulate and maintain the skin’s overall health.


 Common acids found in skin care products include glycolic acid, lactic acid, malic acid, salicylic acid, trichloroacetic acid, and resorcinol.     


Chemical peels can be separated into two groups – organic and aromatic acids – and vary in different skin depths of exfoliation: very superficial, superficial, medium, and deep.


Choosing a chemical peel can be confusing, especially if a skin care professional is not sure what to look for or if unfamiliar with using chemical peels in their services.


What is the Difference Between Organic Acids and Aromatic Acids?


Organic acids contain ingredients like glycolic, lactic, and malic acid (also known as alpha hydroxy acids) that provide nutrients and can perform metabolic functions. Organic acids are considered wounding agents and are grouped as exfoliants because they work from the inside out by detaching the lower layers of the stratum corneum to achieve exfoliation. The results from these peels are light to medium flaking of the skin and not necessarily peeling. The application of these exfoliants is timed, meaning the skin care professional applies the acid solution to the skin and allows it to sit for an amount of time, then removing it. The longer the acid sits on the skin, the deeper the exfoliation.


Aromatic acids contain ingredients such as salicylic acid, trichloroacetic acid, and resorcinol and are highly keratolytic (deeply exfoliating). These acids work by dissolving the stratum corneum layer by layer from the outside and perform a deeper exfoliation. This results in peeling of the skin, which is why they are referred to as chemical peels. The application of these peels is dosed dependent or layered, meaning they are applied layer by layer. The more layers performed, the deeper the peel.




All skin care professionals should understand the basics in chemistry when working with acids and applying them to the skin. Peel solution strengths are determined by pH and pKa values and concentration (percentage) of acid in the solution. Different acids will have different pH and pKa values and will be used in different concentrations.


pH is a measure of hydrogen ion concentration, a measure of the acidity or alkalinity of a solution. The pH scale usually ranges from zero to 14. It is the presence of hydrogen ions in solutions that allows professionals to measure the pH of a solution. The quantity of hydrogen or hydroxyl ions in a solution determines whether the solution is acidic or alkaline (salt).


Acids, bases, and salts are among the most important chemical compounds used by chemists. These compounds contain ions of the element hydrogen. Ions are atoms or molecules that have lost or gained electrons. If atoms lose one or more electrons they become positively charged ions (cations). If atoms gain one or more electrons, they become negatively charged ions (anions).


Acid strength relates to the pKa value. pKa is a measure of acid strength and free acid availability. The pKa is the logarithmic expression of the pH at the point where the acid achieves free acid status containing equal amounts of ion and salt. The pKa has significant relevance in the use of acid because it informs the professional the pH required for an efficacious peeling solution and outcome. For example, an acid with a pH of 3.5 and a pKa at 3.0 indicates that the solution will have more salt than acid. Salt adds no value in an acid solution and its presence only causes more irritation.


The smaller the value of the pKa, the easier it is to remove the proton and the stronger the acid – the larger the value, the weaker the acid. What is important to remember is that pKa values are logarithmic, which means the difference between the strength of an acid with a pKa of 3 compared to a pKa of 4 is 10 times and similarly between a 4 and 5 is also 10 times. This means that a pKa of 3 is 100 times stronger (10 times 10) than a pKa of 5. The following list provides the pKa values that pertain to the most commonly used acids in the professional environment.


  • Glycolic acid (pKa 3.83)
  • Lactic acid (pKa 3.86)
  • Pyruvic acid (pKa 2.49)
  • Citric acid (pKa 3.13)
  • Salicylic acid (pKa 3.0)
  • TCA (pKa 0.26)
  • Resorcinol (pKa 11.27) but keep SB in line with paragraph


The pKa value tells the professional at what pH value equilibrium is achieved between acid and salt (for example half acid and half salt). This translates that if an acid is buffered, some of the acid is converted to the salt form. Buffers and neutralizers are often confused. Buffers are used to stabilize a pH. Neutralizers inactivate an acid substance. When the pH is lower than the pKa, regardless of concentration, there is more acid than salt in a buffered acid solution. Acid solutions are buffered not to make the acid stable but to raise the pH – the concentration is not as important as the pH and the pKa. Often, professionals focus on the pH of a chemical peel, rather than the pKa. Percentage of acid concentration is important, but they also need to understand acid chemistry, which helps explain why a 5% solution of trichloroacetic acid (pKa of 0.26) will be far stronger than lactic acid (pKa 3.86) or glycolic acid (pKa 3.83) at 30%. This is because trichloroacetic acid is almost fully ionized (and the strongest possible acid) and lactic and glycolic acids are less ionized and far weaker.


Understanding acid chemistry will provide insight to how these acids work and why the concentration of acid, pH, pKa, and peel time determine if an acid peel will be effective or not. The combination of these variables all determine the type and depth of the wounds to the epidermis. This all impacts the upper reticular dermis, and duration of exposure, benchmarked by the erythema reaction, will visually provide depth impact of light, medium, or deep.


Understanding acid chemistry, coupled with experience and skill, allows aestheticians to make intelligent decisions applicable to the type, condition, and ethnicity of the skin when applying chemical peels. For this reason alone, know the manufacturer and ensure education in chemical exfoliation is part of their educational curriculum and continue training indefinitely in this subject.


Chemical Peel Depths


Very superficial peels remove part of the outer layer of the stratum corneum. They are the lightest professional exfoliation offered with no downtime. These peels are a great way to introduce clients to the world of chemical peels.


Superficial peels extend into the stratum granulosum and are great for skin that is prepared and ready for more active treatments to achieve regenerative results. Depending on the client and treatment performed, these peels lead to little or no downtime. Light flaking or peeling is expected for a few days post-peel.


Medium depth peels (max four layers) extend through all layers of the epidermis. These chemical peels are the greatest form of exfoliation that most aestheticians can perform. Clients must be prepped and ready to receive these chemical peels, as they will be providing a deep desquamation of the skin.


Deep peels extend through all the layers of the epidermis and into the papillary and reticular layers of the dermis. A deep peel can only be performed by a physician and includes extensive downtime.




Chemical peels can provide mild to drastic results, while managing a variety of skin concerns, and are often more effective than other clinical treatments. A series of peels should always be performed, as chemical peels are not a one-and-done solution. Clients should come in every four to six weeks for treatments to maintain healthy skin until optimal results are reached, followed by monthly treatments yearly to maintain results.


These acids have been studied thoroughly and extensively and have been scientifically substantiated to decrease stratum corneum cohesiveness, increase thickness of viable epidermis, increase deposition of hyaluronic acid, induce reversal of basal cell atypia, increase restoration of rete ridges, and increase secretion of lamellar bodies.


Chemical peels can help improve aging, hyperpigmentation, texture, blemishes, congestion, fine lines and wrinkles, and loss of elasticity.


Organic acids, specifically glycolic and lactic acid, are most commonly used given the many benefits they supply the skin, while creating positive changes through exfoliation. As these acids provide exfoliation, they also play an integral role in bioengineering the stratum corneum, which contributes to the overall health of the skin. In addition, alpha hydroxy acids have no known systemic toxicity and are also classified as antioxidants and fight free radical damage to the skin.




In order to receive a chemical peel, the skin must be prepped and ready. Lack of preparation can lead to issues during and after the treatment, leading to longer healing time. Clients should be using active homecare products – meaning they are using professional-grade products with active ingredients, such as retinols, alpha hydroxy acids, tyrosinase inhibitors, and other professional-grade products, for at least four to six weeks before moderate treatments are performed. These active ingredients begin to prepare the skin to accept the acid solution, increase cellular turnover, and protect the melanocytes, ensuring a successful treatment. Active homecare products are necessary in order to achieve optimum results.


Active Homecare Regimen


A minimum of two to six weeks of active homecare is a must for clients preparing to receive a chemical peel. Their routine should include at least four steps and their homecare products should contain ingredients like glycolic acid, lactic acid, malic acid, retinol, vitamin C, ceramides, peptides, and sunscreen. Using a four-step system is important for a client’s skin health.


Example of Homecare Regimen


Cleanse: Clients should use an active and calming cleanser in their regimen to wash away debris and slough off dead skin cells. Active cleansers are not enough on their own – every client should have an active leave-on product that is used several times a week.


Treat: These products keep skin active, begin prepping the skin for cellular turnover, and begin addressing concerns. This step should consist of serums that are left on the skin and not removed.


Balance: Balancing the skin is just as important as prepping the skin. Clients should have a moisturizer that repairs the skin’s barrier with ingredients like ceramides, hyaluronic acid, peptides, and vitamin C to ensure the skin’s health.


Protect: Clients should apply sunscreen to prevent ultraviolet damage and protect skin daily. This critical step should be done every morning and reapplied if they will be spending time outside.


Thorough Skin Analysis


In addition to clients being on a committed homecare regimen, it is important to perform a thorough skin analysis to determine the appropriate peel for the client. Having a thorough skin health questionnaire will help to prevent issues in the treatment room and help to determine the appropriate peel solution. As the professional, it is important to identify the client’s skin type (normal, dry, sensitive, combination, or oily), their Fitzpatrick type, and the age of their skin (Glogaue or Rubin scales), and finish with an explanation of realistic expectations for their treatment.


 Not every skin concern and problem can be solved with one single chemical peel. It is inappropriate to assume that one peel is a one-size-fits-all and professionals should carry a variety of peels for different concerns and skin types.




Half of the results of treatments depend on how well clients take care of their skin at home afterward. Make sure a client has the proper products to care for, protect, and heal their skin after their treatment. These products will be different from their active products. Clients should continue to follow a four-step regimen, but one that contains healing ingredients to support wound healing and prevent issues like post-inflammatory hyperpigmentation.


Homecare products should contain ingredients like ceramides, peptides, fatty acids, lipids, semi-occlusive, vitamin C, tyrosinase inhibitors, and hyaluronic acid.


Clients should also receive a handout with reminders on how to protect their skin during the duration of the healing process. This should include steps to remember after any level of peel, such as: avoid all sun exposure; avoid exercise and sweating for 48 to 72 hours; avoid baths and try to prevent the shower from spraying directly onto the treated area; do not pick, scratch, rub, or unnecessarily touch the face; and minimize facial expression. It should also offer tips for how to heal skin faster, like: keep skin moisturized with lipids, fatty acids, ceramides, and hyaluronic acid; always apply an occlusive barrier on top of a moisturizer; wear and reapply sunscreen every two hours; and apply gentle enzymes for three days post-peel, until peeling has stopped to naturally exfoliate the skin.




Knowing who can and cannot receive a chemical peel is just as important as selecting the right chemical peel treatment for the client. There are a number of contraindications that can exclude a client from receiving a treatment. It is important to not only have an open dialog with a client about these contradictions, but they should also be included in the spa’s skin health questionnaire.


A list of contraindications for chemical peels includes:


  • Accutane (within the last year)
  • pregnancy
  • breastfeeding (some limitations)
  • chemotherapy
  • Retin-A
  • sunburn
  • open sores and wounds
  • aspirin allergy (Jessner and salicylic peels)
  • heart condition (Jessner and salicylic peels)
  • active cold sores
  • some autoimmune diseases
  • recent facial surgical procedures


In conclusion, chemical peeling has been proven to be safe and effective within a professional skin care environment for photoaging, acne, pigmentation, rosacea, and many other skin conditions traditionally treated with dispensed prescriptions and can achieve the same result. Aestheticians must understand chemical peels and use this skill with good judgment to properly select the correct peel solution for their clients’ skin type and ethnicity according to epidermal thickness and sensitivity.



Sarah Robbins




Sarah Robbins is the director of the Institute of Skin Science at GlyMed Plus and is also a licensed master aesthetician in the state of Utah. She received her license from one of the top aesthetics schools and has over nine years of experience in the aesthetics industry. Her passion for understanding skin histology has helped others to expand their knowledge when working with products and ingredients. She loves learning and dedicates her time to making education fun and understandable. “Being an educator is a privilege and true success is empowering others to grow.”

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