Peel Science

Contact Author Gül Ç. Zone February 2014 issue of Skin Inc. magazine

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Peel Science

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Chemical peels remain some of the most effective, efficient and financially feasible skin care treatments available, and understanding the science behind them allows skin care professionals to most effectively manage, market and take advantage of this powerful, lucrative tool.

Skin, like any material, is subject to wear and tear, chemical and photo degradation, and absorption of chemical pollutants, not to mention microbial invasion. Fortunately, this natural “material” has the benefit of re-building itself through an influx of new cells from the basal layer of the epidermis. However, with age, this constant supply of new cells slows, and a degraded and disorganized skin surface becomes more of the norm. This is where chemical peels—both acid and nonacid—work their magic. Beginning by simply removing the top layer of the epidermis, the skin will exhibit some of its former luster and uniformity, much as the light sanding of an old wooden surface will return some of its finish and surface quality. As a peel works deeper into the epidermis, the lower skin layer loosens and the basal layer of the skin is stimulated to produce new cells. The appearance of new cells can replace aged, oxidized and hyperpigmented skin. The end result is more cellular bulk, offsetting the epidermal thinning that comes with aging; hydrating skin; and improving color uniformity and smoothness.

Peel chemistry

The most common types of chemical peels are acid peels, which work to remove the cells of the top layer of skin’s upper epidermis by breaking weak chemical bonds that hold together the epidermal skin cells, termed “corneocytes” or “keratinocytes.” Depending on the strength, pH and delivery agent of the peel product, upon application, the skin cells delaminate and lift away. (See Figure 1.) As the peel process proceeds, or upon subsequent treatment, it can penetrate further into the thickness of the epidermis to interact and weaken the bonds holding together the cells of the lower layers of the epidermis.


The strength of an acid peel is based on several factors:

  1. The concentration of the active ingredient;
  2. The type of peel agent;
  3. The pH of the product; and
  4. The delivery system.

The concentration refers to the amount of free acid found in the peel, as determined by an analytical method called titration. As the concentration of the acid increases, the strength increases. This strength is characterized by the pH of the product, a chemical parameter that defines the acidity or basicity of an aqueous solution. The lower the pH of the product, the stronger the acid, which is counterintuitive. By definition, the lower the pH of an acid system, the more it wants to release its hydrogen ion (H+), which can then interact and react with the chemical bonds that hold the skin cells together. Conversely, the higher the pH an acid exhibits, the more the acid will tend to hold its hydrogen ion, and it is considered more basic. As shown in Figure 2, the pH scale shows the range of pH values, with 0 being the most acidic, 7 being neutral and 14 the most basic. Most acid-based chemical peels have pHs ranging from 1.5–4.0.

It is important to remember that stronger is not always better when it comes to peels, as evidenced in the treatment of hyperpigmentation, which can be a challenge to many skin care professionals. Trichloracetic acid (TCA) peels can effectively lift off and remove pigmented skin cells that have progressed through the skin’s natural maturation cycle; however, they can be counterproductive when working with higher Fitzpatrick skin colors or in types where melanocytes are easily triggered due to inflammatory responses in the skin by these aggressive peeling agents. Another approach may be to perform lighter, less aggressive peels that progress over a period of time to achieve better long-term results.

Peel ingredients

For the esthetic practice, there are a wide range of acid and nonacid ingredients available, and many have secondary benefits, such as antibacterial or skin-lightening properties. Esthetic peels are less aggressive than medical peels and act only superficially on the upper epidermis, but they provide the esthetician with more control of treatment results. Esthetic peels include mild enzyme peels, which affect only the upper stratum of the epidermis; acid peels, which target the epidermis from the outer surface inward; and nonacids, such as retinol or retinoic acid (vitamin A derivatives), which target the lower layers of the epidermis to kick start the basal stem cells, and initiate new cell replication that forces cells to the outer surface, thus affecting a natural peel.

Peel systems

The main families of chemical peel systems include the ubiquitous alpha hydroxy acids (AHAs), including glycolic and lactic acid; carboxylic and dicarboxylic acids; beta hydroxy acids (BHAs); and blends with other acids and ingredients. See Common Active Peel Ingredients.

Azelaic peels, based on azelaic acid, a dicarboxylic acid, represent one of several peel acids with multiple benefits. It promotes a mild peel of the upper layer of the epidermis, and it can also offset post-inflammatory hyperpigmentation (PIH), a problem that can plague a peel process, particularly in pigmented skin. Azelaic acid is able to inhibit a key enzyme needed in the skin’s pigmentation process—tyrosinase—slowing excess pigmentation by reducing melanin production. Another mild acid, kojic acid, is also used in skin care products to affect mild peeling while exhibiting strong tyrosinase-inhibition and anti-inflammatory properties.

In addition to preventing hyperpigmentation, some of the acid systems are effective as anti-acne treatments. The antibacterial properties of azelaic acid, particularly at lower pHs, are very effective against skin bacteria often associated with acne, such as propionibacterium. The peeling effect of the acid helps remove the initial sebum/epidermal plug that precedes the acne comedone, but also is effective at suppressing bacteria growth at the site. Salicyclic acid, a BHA with unique oil solubility that common AHAs do not have, is also an effective acne treatment. Mandelic acid, an aromatic keto-acid, has been shown to have both antibacterial and bacteriostatic properties.

Medical peels

By definition, medical peels are peel treatments carried out in a medical spa or physician’s clinic. A medical peel can be characterized as an aggressive peel that may not only penetrate the full thickness of the epidermis, but can also quickly impact the dermis and should be conducted with the oversight of a practicing physician trained in dermatology or plastic surgery. A medical peel is typically used when less aggressive methods are ineffective for treatment of conditions such as profoundly photodamaged, or naturally damaged or scarred skin. They are characterized as medium-to-deep depth peels and are performed under anesthesia. Glycolic acid and TCA peels at higher concentrations are usually classified as medium depth, while phenol peels and modified phenol peels—such as the Gordon-Baker or Hetter formulas—are the most common deep medical peels.

Understanding the nuances

Advances in peel treatments now emphasize both the superficial wounding effect a peel produces, and the benefits of healing and reducing inflammation afterward to improve both immediate and long-term results. Understanding and respecting the tremendous benefits of peels, as well as their potential to harm if applied improperly, is a responsibility of all skin care professionals. Continued education in peel science and hands-on training should be incorporated, as well as learning the impact of a peel on the substructures of skin to help in the understanding of the fine nuances of this powerful treatment technology and allow the skin care professional to continue to provide this service at an exceptional level.

G%C3%BCl+C.+ZonePresident and founder of Ecozone, Inc. and Dermaware Bio-Targeted Skin Care, Gül Ç. Zone has combined her biomedical formulary background and cosmetic marketing expertise to develop Dermaware corrective skin care for esthetic spa and medical practitioners. Her knowledge has also contributed to the development of several international skin care lines.

Related Content



Peel Science—Figure 1

Illustration of the surface breakdown of the epidermis with acid product.

Peel Science—Figure 2

The pH and hydrogen ion concentration as it relates to acidity and basicity.

Online Exclusive: Do You Know How to Peel?

Gül Ç. Zone answers common questions from skin care professionals about the education behind offering chemical peels.


Q: What type of training is involved in learning how to perform peels?

A: Both theoretical and hands-on training is recommended. Peel certification classes should be a part of every esthetician’s continued education courses. Reading about peels is just the first step in learning how to work with peels. More importantly, it is imperative to gain the hands-on experience. The same peel may have a different effect on two similar skin types. Another focus in advanced continued education classes is also how to customize results by combining different peel modalities.


Q: How should peels be performed?

A: Individually: Single treatments performed with intervals greater than two weeks. Recommended for maintenance. Progressive: Series of treatments spaced 7-10 days apart where each service is progressively stronger. Recommended for corrective clinical applications.


Q: Who should have a peel?

A: Every individual can have a peel. The key is to match the correct peel to the skin type and lifestyle of the individual. Even the most sensitive skin types can benefit from peels. Always perform a patch test to check compatibility. Always fill out a skin analysis and health intake form before performing a peel.


Q: Is there anyone who should not have a peel?

A: A peel is, by definition, the controlled, superficial wounding of the skin using chemical substances. Therefore, any individual who already has “wounded” skin, whether from an acne lesion, waxing, cosmetic injections or any other aggressive skin care treatment modality should not have a peel. Any person taking isotretinoin or using topical applications of tretinoin or retinoic acid should not have a peel. If concerned with any medical issues, request a release from the client’s doctor.


Q: How do you prepare skin for a peel?

A: Prepare the skin by placing clients on a corrective regimen 1–2 weeks prior to their peel to maximize skin health and precondition with daily exfoliating elements, including mild peeling agents and retinoids. Also, start the regeneration process prior to a peel with a good corrective home care regimen.


Q: How do you take care of skin post-peel?

A: The post-peel regiment should include healing treatments that help the skin repair itself. We know the skin’s natural repair mechanisms slow down considerably with age. It is critical to provide as much aid as possible to the skin that we intentionally wound. A good post peel regimen will have bioactive elements that heal the skin from the inside out, as well as provide a temporary barrier to protect the skin from UV and help retail the skin’s natural moisture.


Words of caution: As a professional, make sure that you have peeling and healing products in your treatment room and on your retail shelves for the client to take home. Often, skin care professionals focus only on the peeling and want to skip the healing. This is a big mistake as the best results are associated with the best healing. When you have what you need at your fingertips prior to performing a treatment, there is never any guessing or substituting at the time of the peel. A peel can be safe if the esthetician has the proper training and products to perform the treatments. It is also imperative that the skin care professional educate their client to ensure maximum compliance pre- and post-peel. This education should be given both verbally and in writing.

Peel Science—Common Active Peel Ingredients

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