The skincare industry has seen a remarkable evolution, with science at its core. Among the many scientifically-backed treatments available, chemical peels have gained significant popularity.
Introduction
The skincare industry has seen a remarkable evolution, with science at its core. Among the many scientifically-backed treatments available, chemical peels have gained significant popularity. These peels, formulated with a range of acids like phenol, trichloroacetic acid (TCA), glycolic acid, and other alpha hydroxy acids (AHAs), work on a molecular level to exfoliate, rejuvenate, and enhance skin texture and appearance. But what exactly is happening when you apply these acids to the skin? Here, we’ll take a deep dive into the chemistry of chemical peels, exploring how they work, their differences, and what makes each one unique.
This blog is intended for educational purposes only and does not constitute medical advice. Consult with a licensed dermatologist before undergoing any chemical peel.
Chemical peels involve applying a solution to the skin that initiates controlled exfoliation. The outermost layer of the skin, known as the stratum corneum, is composed of dead skin cells that protect underlying layers. Peels use acids to break down the bonds between these cells, shedding the top layer and revealing smoother, more even skin beneath.
Chemical peels are classified into three categories based on their depth of action:
Superficial Peels: Target the epidermis (outermost skin layer). They’re often mild and contain gentle AHAs or other light acids, ideal for enhancing glow and improving minor texture issues.
Medium Peels: Penetrate the upper dermis and provide more substantial results for issues like hyperpigmentation, sun damage, and fine lines.
Deep Peels: Affect both the epidermis and deeper layers of the dermis, offering more dramatic results but with longer recovery times. They’re often used for severe acne scars or deep wrinkles.
Each type of peel involves unique chemical interactions depending on the chosen acid. Let’s look at some of the most popular acids used in chemical peels and how they work on a molecular level.
Phenol peels are deep chemical peels often reserved for serious skin issues like deep wrinkles, severe acne scars, or significant sun damage. Phenol (C₆H₅OH), also known as carbolic acid, is a potent organic compound with high acidic strength that can penetrate deeply into the skin.
How Phenol Peels Work:
When applied, phenol disrupts the cellular bonds in the outer and mid-dermal layers. Because it penetrates so deeply, it can remove the outer layer of skin and significantly boost collagen production, leading to a tightening effect. However, phenol peels also come with considerable side effects due to their potency, including a higher risk of irritation, extended recovery time, and potential for skin lightening.
The Chemistry Behind Phenol Peels:
Phenol’s chemical structure allows it to penetrate the lipid layers of the skin efficiently. However, this also makes it more likely to irritate sensitive skin. Due to its high reactivity, phenol also has the potential to disrupt cellular proteins. As these proteins break down, the outer layer of skin is shed, stimulating new cell turnover and collagen synthesis in the dermis, where wrinkles and scars are most deeply set.
Trichloroacetic acid (TCA) is a widely used acid for medium-depth chemical peels. Structurally, TCA is similar to acetic acid (the acid in vinegar) but with three chlorine atoms attached, making it much stronger. TCA peels are effective for treating hyperpigmentation, fine lines, and sun damage with a relatively moderate recovery time compared to phenol peels.
How TCA Peels Work:
When applied to the skin, TCA causes protein denaturation. This reaction disrupts cellular cohesion in the epidermis, leading to peeling. As the skin sheds, new cells rise to the surface, resulting in an even-toned, smoother complexion. Since TCA affects the upper layers of the dermis, it stimulates collagen production as well, providing a mild tightening effect.
The Chemistry Behind TCA Peels:
TCA’s tri-chlorinated structure gives it strong keratolytic properties, meaning it efficiently breaks down keratin bonds within the skin. Once TCA reaches the target skin depth, it initiates a process of coagulation in proteins, leading to controlled cell necrosis. This reaction is essential for stimulating the rejuvenation process, as the dead cells are replaced with new, healthier ones.
Glycolic acid, one of the most popular ingredients in skincare, is an alpha hydroxy acid (AHA) derived from sugar cane. Known for its small molecular size, glycolic acid penetrates the skin easily, making it ideal for superficial to medium peels. It’s often used to brighten the skin, improve texture, and reduce mild hyperpigmentation.
How Glycolic Acid Peels Work:
Glycolic acid works by loosening the "glue" that binds dead skin cells together. Because it doesn’t penetrate as deeply as TCA or phenol, glycolic acid is milder and typically requires less recovery time, making it suitable for a broader range of skin types and concerns.
The Chemistry Behind Glycolic Acid Peels:
As a small molecule with a simple structure (HOCH₂COOH), glycolic acid efficiently disrupts the intercellular matrix of the stratum corneum, leading to exfoliation. The chemical bond-breaking process encourages the skin to shed its outer layer while also stimulating fibroblasts to produce collagen in the dermis. Over time, this can lead to firmer, more youthful skin, with minimal irritation for most skin types.
Lactic acid, derived from milk, is another popular alpha hydroxy acid used in superficial peels. Its larger molecular size makes it less penetrating than glycolic acid, making it suitable for sensitive skin. Lactic acid peels can brighten the skin and improve hydration while gently exfoliating.
The Chemistry: Lactic acid has an additional hydroxyl group, making it more hydrophilic and therefore less penetrative. It primarily acts on the surface of the skin, offering gentle exfoliation.
Salicylic acid, commonly found in acne treatments, is a beta hydroxy acid (BHA). Unlike AHAs, BHAs are oil-soluble, allowing them to penetrate pores effectively. Salicylic acid peels are ideal for treating acne-prone skin and reducing the appearance of blackheads and pores.
The Chemistry: Salicylic acid’s lipophilic nature allows it to dissolve within sebum, reaching the sebaceous glands. It has a desmolytic effect, breaking down desmosomes (the structures that bind skin cells), which makes it highly effective for pore-clearing.
Mandelic acid, derived from bitter almonds, is a larger AHA molecule. Due to its size, it penetrates the skin slowly, making it less likely to cause irritation. Mandelic acid is particularly suited for sensitive and darker skin tones and can treat acne, pigmentation, and signs of aging.
The Chemistry: Mandelic acid’s bulky structure slows down its absorption, reducing its reactivity and making it gentler. It works on the skin’s surface, breaking down keratinized cells for mild exfoliation.
Jessner’s peel is a combination of salicylic acid, lactic acid, and resorcinol in an ethanol solution, creating a medium-depth peel. It’s effective for treating acne scars, pigmentation, and fine lines due to the synergy of the acids involved.
The Chemistry: This blend works by simultaneously exfoliating, penetrating oil glands, and inducing controlled damage to the epidermis. The ethanol base enhances the absorption of the active ingredients, allowing them to penetrate more effectively than each would on its own.
While chemical peels can deliver impressive results, it’s essential to understand that each type of peel carries risks. Here are some potential side effects and considerations:
Irritation and Redness: Mild peels may cause temporary redness, while deeper peels can lead to more prolonged irritation.
Hyperpigmentation: In darker skin tones, chemical peels, particularly those with phenol and TCA, may result in post-inflammatory hyperpigmentation if not administered carefully.
Sun Sensitivity: Acid peels make the skin more susceptible to UV damage, so sunscreen is crucial after treatment.
Scarring: Though rare, deeper peels can potentially cause scarring, particularly if the skin does not heal properly.
Infections: Deep peels like phenol may compromise the skin’s natural barrier, increasing the risk of infection if not managed in a sterile environment.
It’s essential to consult with a licensed dermatologist to determine the best peel type and concentration based on individual
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