# Chemical Peels: Superficial, Medium, and Deep

## Introduction

Chemical peeling is a controlled application of a caustic agent to the skin to induce a predictable depth of tissue destruction, followed by regeneration and remodeling. The depth of the peel determines both the therapeutic efficacy and the risk profile. Chemical peels remain a cornerstone of cosmetic dermatology for photoaging, dyschromia, acne scarring, and precancerous lesions.

## Classification by Depth

### Superficial Peels (Epidermis Only)

Superficial peels destroy the epidermis to the **basal layer** or upper papillary dermis. They require minimal downtime (3 to 5 days of mild desquamation) and are useful for acne, melasma, mild photoaging, and texture improvement. **Agents** include glycolic acid (20 to 70%), salicylic acid (20 to 30%), Jessner solution, TCA 10 to 25%, lactic acid, and mandelic acid.

### Medium-Depth Peels (Papillary Dermis)

Medium-depth peels penetrate through the epidermis to the **upper reticular dermis**. Downtime is 7 to 10 days with significant erythema and crusting. They are useful for moderate photoaging, actinic keratoses, superficial scarring, and moderate dyschromia. **Agents** include TCA 35 to 50% (alone or in combination), the Jessner plus TCA 35% Monheit combination, and glycolic 70% plus TCA 35%.

### Deep Peels (Mid-Reticular Dermis)

Deep peels penetrate to the **mid-reticular dermis** with extended downtime of 2 to 3 weeks and significant risk of complications. They are useful for severe photoaging, deep rhytides, and acne scarring. **Agents** include the Baker-Gordon phenol formula (88% phenol with croton oil, septisol, and water). High-concentration TCA above 50% has been largely abandoned due to unpredictable scarring.

| Peel Depth | Target Level | Agents | Downtime | Indications | Skin Type Safety |
|-----------|-------------|--------|----------|-------------|-----------------|
| Superficial | Epidermis/upper papillary dermis | Glycolic 20–70%, salicylic 20–30%, Jessner, TCA 10–25% | 3–5 days | Acne, melasma, mild photoaging | All types (caution IV–VI) |
| Medium | Papillary to upper reticular dermis | TCA 35–50%, Jessner + TCA 35%, glycolic 70% + TCA 35% | 7–10 days | Moderate photoaging, AKs, scarring | Types I–IV (caution IV) |
| Deep | Mid-reticular dermis | Baker-Gordon phenol | 2–3 weeks | Severe photoaging, deep rhytides | Types I–III only |

## Key Peeling Agents

### Glycolic Acid (Alpha-Hydroxy Acid)

Glycolic acid decreases corneocyte cohesion and, at higher concentrations, causes epidermolysis. **Concentrations** range from 20 to 70%, with depth depending on concentration, contact time, and skin preparation. It **must be neutralized** with sodium bicarbonate or water to stop the reaction. Free acid formulations are more potent than buffered or partially neutralized products.

### Salicylic Acid (Beta-Hydroxy Acid)

Salicylic acid is **lipophilic**, providing excellent penetration of sebaceous follicles. It is **self-limiting**, producing a white pseudofrost that limits further penetration. Concentrations of 20 to 30% are used for superficial peeling. It is particularly effective for **acne and oily skin** due to its anti-inflammatory properties. Caution is warranted for the theoretical risk of **salicylism** with extensive application, though this is rare.

### Jessner Solution

Jessner solution contains **14% resorcinol, 14% salicylic acid, and 14% lactic acid in ethanol**. It disrupts the epidermal barrier and is used alone for superficial peeling or as a primer before TCA for medium-depth peels. Modified Jessner solutions substitute citric acid for resorcinol to reduce sensitization risk.

### Trichloroacetic Acid (TCA)

TCA works through **protein denaturation and coagulative necrosis**. Depth is concentration-dependent: 10 to 25% produces a superficial peel, 35 to 50% a medium peel, and above 50% a deep peel (not recommended). TCA is **self-neutralizing**, requiring no chemical neutralization since the reaction stops when all proteins in the target depth are denatured. **Frosting levels** provide real-time depth assessment: Level I (erythema with streaky white frost) indicates superficial depth, Level II (white frost with erythema showing through) indicates papillary dermal depth, and Level III (solid white frost with no background erythema) indicates reticular dermal depth. TCA can also be applied focally using the **CROSS technique** (Chemical Reconstruction of Skin Scars), where 70 to 100% TCA is applied focally in ice-pick acne scars.

<image>Clinical progression of TCA peel frosting levels: Level I showing erythema with streaky white frost, Level II showing white coat with pink showing through, and Level III showing solid white enamel frost indicating reticular dermal penetration</image>

### Phenol (Deep Peel)

The **Baker-Gordon formula** consists of 3 mL of 88% phenol, 2 mL of tap water, 8 drops of liquid soap, and 3 drops of croton oil. Croton oil is the primary determinant of depth (the active "peeling agent"), while phenol serves as the vehicle. **Cardiac toxicity** is a critical concern: phenol is hepatically metabolized, and rapid systemic absorption can cause **cardiac arrhythmias** including premature ventricular contractions and ventricular tachycardia. The peel must be applied slowly with **cardiac monitoring**, IV hydration, and staged facial application over 60 to 90 minutes. It produces the most dramatic improvement in deep rhytides but carries the highest risk.

## Prepeel Assessment and Preparation

### Patient Selection

**Fitzpatrick skin type** is a critical consideration: lower types (I to III) are ideal candidates for medium and deep peels, while higher skin types (IV to VI) carry significantly increased risk of **post-inflammatory hyperpigmentation**. The history should include isotretinoin use within 6 to 12 months (controversial but caution warranted), herpes simplex history, keloid tendency, and recent facial procedures. The **Glogau photoaging classification** guides depth selection.

### Skin Priming

**Topical retinoids** (tretinoin 0.025 to 0.05%) applied for 2 to 6 weeks thin the stratum corneum, promote uniform penetration, and accelerate healing. **Hydroquinone 4%** used for 2 to 6 weeks reduces melanocyte activity and decreases PIH risk, and is essential for skin types III to VI. Retinoids should be **discontinued** 3 to 5 days before medium and deep peels. **Antiviral prophylaxis** with valacyclovir 500 mg twice daily starting 1 day before and continuing 7 to 14 days is indicated for medium and deep peels for all patients, not just those who are HSV-positive.

<image>Diagram showing cross-section of skin with depth of injury produced by different peeling agents: glycolic acid and salicylic acid affecting the epidermis, TCA 35% and Jessner-TCA reaching the papillary dermis, and Baker-Gordon phenol reaching the mid-reticular dermis</image>

## Technique Considerations

Thorough **degreasing** with acetone or alcohol removes oils and ensures uniform penetration. **Application** is performed with gauze sponges, cotton-tipped applicators, or fan brushes, applied in cosmetic subunits. **Endpoint recognition** relies on frosting levels for TCA and on erythema and epidermolysis for glycolic acid. **Feathering** blends the peel into adjacent untreated areas to avoid lines of demarcation.

## Complications

### Early Complications

**Herpes simplex reactivation** can occur even without a history of HSV, making prophylaxis mandatory for medium and deep peels. **Bacterial infection** with Staphylococcus, Streptococcus, or Pseudomonas should be monitored by watching for delayed healing, purulence, and pain. **Contact dermatitis** may develop from topical agents used in postpeel care. **Prolonged erythema** persisting beyond 3 weeks for superficial peels or beyond 2 months for medium peels may signal impending scarring.

### Late Complications

**Post-inflammatory hyperpigmentation** is the most common complication in skin of color and is treated with hydroquinone, retinoids, and sun avoidance. **Hypopigmentation** is especially common after deep phenol peels, is often permanent, and produces a characteristic line of demarcation at the jawline. **Scarring**, particularly hypertrophic scars, is most common on the upper lip, chin, and periorbital areas and is treated with silicone sheeting and intralesional triamcinolone. **Textural changes** including a waxy, alabaster appearance may follow deep peels.

<image>Before and after photographs demonstrating medium-depth chemical peel results for moderate facial photoaging, showing improvement in fine rhytides, lentigines, and overall skin texture at 3 months post-procedure</image>

## Key Clinical Pearls

TCA is self-neutralizing while glycolic acid must be neutralized, and failure to neutralize glycolic acid leads to uncontrolled deepening of the peel. Frosting level is the best real-time indicator of TCA peel depth, with a solid white Level III frost indicating reticular dermal injury. All patients undergoing medium or deep peels should receive antiviral prophylaxis regardless of HSV history. The CROSS technique using focal high-concentration TCA is an effective treatment for ice-pick acne scars. Phenol peels require cardiac monitoring because arrhythmias from systemic absorption are the most dangerous complication.

## References

1. Monheit GD. Medium-depth chemical peels. *Dermatol Clin*. 2001;19(3):413-425.
2. Landau M. Chemical peels. *Clin Dermatol*. 2008;26(2):200-208.
3. Hantash BM, Stewart DB, Cooper ZA, et al. Facial resurfacing using the croton oil-phenol peel. *Plast Reconstr Surg*. 2011;128(3):351e-359e.
4. Soleymani T, Lanoue J, Rahman Z. A practical approach to chemical peels: a review of fundamentals and step-by-step algorithmic protocol for treatment. *J Clin Aesthet Dermatol*. 2018;11(8):21-28.