Tuesday, 29 December 2020 09:40

Understanding Chemical Peels

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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.  

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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. When you exercise, your body functions better and your health is maintained. Exfoliating the skin helps to regulate and maintain the skin’s overall health.

 Common acids found in skincare products:

  • Glycolic Acid
  • Lactic Acid
  • Malic Acid
  • Salicylic Acid
  • Trichloroacetic Acid
  • Resorcinol

Chemical Peels can be separated into two groups and vary in different skin depths of exfoliation.

Groups: Organic Acids & Aromatic Acids

Depths: Very Superficial, Superficial, Medium & Deep

Choosing a chemical peel can be confusing, especially if you don’t know what to look for or if you’re unfamiliar with using chemical peels in your 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 or AHAs) 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 you apply the acid solution to the skin and allow it to sit for an amount of time, then remove 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 you apply them 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 0 to 14. It is the presence of the hydrogen ions in solutions that allows us to measure the pH of a solution. The quantity of hydrogen or hydroxyl ions in a solution determines whether the solution is acid 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 you of the pH required for an efficacious peeling solution and outcome. For example; an acid with a pH of 3.5 and a pKa @ 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 ten 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

The pKa value tells you at what pH value you achieve equilibrium between acid and salt (ie half acid and half salt). This translates that if you buffer an acid you convert some of the acid 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, you have 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 pKaOften times as professionals we focus on the pH of a chemical peel, rather than the pKa. Percentage of acid concentration is important, but you need to also understand ‘acid chemistry’ which helps explains why a 5% solution of TCA, or trichloroacetic acid (pKa of .26) will be far stronger than lactic acid (pKa 3.86) or glycolic acid (pKa 3.83) at 30%. This is because TCA 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 you insight to how these acids work and why the concentration of acid, pH, pKa and peel time determine if your 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 allow estheticians to make intelligent decisions applicable to the type, condition and ethnicity of the skin when applying chemical peels. For this reason alone, know your manufacturer and ensure education in chemical exfoliation is part of their educational curriculum and continue your training indefinitely in this subject.

Chemical Peel Depths 

0: Very Superficial

Removes part of the outer layer of the Stratum Corneum

The lightest professional exfoliation offered with no downtime. These peels are a great way to introduce clients to the world of chemical peels. 

1: Superficial Peels

Chemical Exfoliant or Peel extends into the Stratum Granulosum

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 down time. Light flaking or peeling is expected for a few days post peel. 

2: Medium Depth Peels

(Max 4 layers)

Chemical Peel extends 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. 

3: Deep Peels

Extends 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 down time. 


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 4-6 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 (HA)

Induce reversal of basal cell atypia

Increases restoration of rete ridges

Increase Secretion of Lamellar bodies

  Chemical peels can help improve:

  • • Aging
  • • Hyper-pigmentation
  • • Texture
  • • Blemishes
  • • Congestion
  • • Fine lines and wrinkles
  • • Loss of elasticity

Organic acids, specifically Glycolic & 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, AHA acids have no known systemic toxicity and are also classified as an antioxidant 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, etc.,for at least 4-6 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

  • Minimum of 2 to 6 weeks is a must
  • Should include at least 4 steps

Homecare products should contain ingredients like:

  • Glycolic Acid
  • Lactic Acid
  • Malic Acid
  • Retinol
  • Vitamin C
  • Ceramides
  • Peptides
  • SPF

Using a 4-step system is important for your clients skin health. 

Example of home care regimen:

Step 1: 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's used several times a week.

Step 2: Treat

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

Step 3: 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..

Step 4: Protect

Apply SPF to prevent UV damage and protect skin daily. This critical step should be done every morning and reapplied if spending time outside. 

In addition to clients being on a committed homecare regimen, it’s 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’s important to identify the clients skin type (normal, dry, sensitive, combination or oily), their Fitzpatrick type (Fitzparick scale 1-6), the “age of the skin” (Glogaue or Rubin Scales), and finish with explanation of realistic expectations for the treatment to the client.

 Not every skin concern and problem can be solved with one single chemical peel. It’s 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 your 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 4-step regimen but one that contains healing ingredients to support wound healing and prevent issues like post inflammatory hyperpigmentation, (PIH). 

Homecare products should contain ingredients like:

  • Ceramides
  • Peptides
  • Fatty Acids
  • Lipids
  • Semi-Occlusive
  • Vitamin C
  • Tyrosinase Inhibitors
  • Hyaluronic Acid

Clients should also receive a handout with reminders on “how to” protect their skin during the duration of the healing process.

Steps to remember after any level of peel:

  • 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
  • Minimize facial expression

How to heal skin faster:

  • Keep skin moisturized with lipids, fatty acids, ceramides, and hyaluronic acid
  • Always provide an occlusive barrier on top of your moisturizer
  • Wear and reapply sunscreen every 2 hours - this is critical
  • Apply gentle enzymes for 3 days post peel, until peeling has stopped to naturally exfoliate the skin


Knowing who can and can’t 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’s important to not only have an open dialog with your client about these contradictions, but they should also be included in your skin health questionnaire.


  • Accutane (within the last year)
  • Pregnancy
  • Breastfeeding (some limitations)
  • Chemotherapy
  • Retin A
  • Sunburn
  • Open sores/wounds
  • Aspirin Allergy (Jessner & Salicylic Peels)
  • Heart Condition (Jessner & 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 photo-aging, acne, pigmentation, rosacea and many other skin conditions traditionally treated with dispensed prescriptions and achieve the same result. Aestheticians must understand chemical peels, use this skill and good judgment to properly select the correct peel solution for their clients skin type and ethnicity according to epidermal thickness and sensitivity.


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