# Chemical Peels and Skin Resurfacing

## Introduction

**Chemical peels** involve the controlled application of chemical agents to the skin to produce a predictable depth of tissue destruction followed by regeneration and remodeling. Classified by depth of penetration: **superficial** (epidermis), **medium** (papillary dermis), and **deep** (reticular dermis). Indications include **photoaging**, dyschromia, acne scarring, fine rhytides, and premalignant actinic keratoses. Understanding of **skin histology**, wound healing, and the Fitzpatrick skin typing system is essential. Adjunctive resurfacing modalities include **dermabrasion**, **laser resurfacing**, and **microneedling**.

## Skin Anatomy and Wound Healing

### Relevant Histology

**Epidermis**: stratified squamous epithelium; thickness 0.04-0.16 mm; contains melanocytes in the basal layer. **Papillary dermis**: thin collagen fibers, ground substance, and superficial vascular plexus; extends to ~0.3 mm. **Reticular dermis**: dense collagen bundles, elastic fibers; extends to 1-4 mm depending on body site. **Adnexal structures** (hair follicles, sebaceous glands, eccrine glands) serve as reservoirs for re-epithelialization.

Areas with **fewer adnexal structures** (eyelids, dorsal hands, neck) are at higher risk for scarring after deep resurfacing.

### Wound Healing After Chemical Peels

Superficial peels: re-epithelialization in **3-5 days** from intact adnexal structures and wound margins. Medium peels: re-epithelialization in **7-10 days**; neocollagen formation begins at 2-3 weeks. Deep peels: re-epithelialization in **10-14 days**; prolonged erythema (2-3 months); significant collagen remodeling over 6-12 months. **Melanocyte recovery** is slower than keratinocyte regeneration; sun protection is critical during this period.

## Preoperative Assessment

**Fitzpatrick skin type** classification (I-VI): higher types (IV-VI) are at increased risk for **post-inflammatory hyperpigmentation (PIH)**. **Glogau photoaging classification** guides treatment depth selection. Pretreatment with **tretinoin (0.025-0.05%)** for 4-6 weeks enhances epidermal turnover and promotes even peel penetration. **Hydroquinone 4%** pretreatment for 4-6 weeks in Fitzpatrick III-VI to suppress melanocyte activity and reduce PIH risk.

History of **herpes simplex virus**: antiviral prophylaxis (valacyclovir 500 mg BID) starting 1-2 days before and continuing 7-14 days after medium or deep peels. **Isotretinoin**: historically recommended waiting 6-12 months after cessation; recent evidence suggests **6 months** is sufficient for medium-depth peels.

## Chemical Peel Agents

| Peel Depth | Penetration | Agents | Healing Time | Best For |
|------------|-------------|--------|:------------:|----------|
| Superficial | Epidermis | Glycolic acid 20-70%, salicylic acid, Jessner's, TCA 10-25% | 3-5 days | Mild photoaging, maintenance |
| Medium | Papillary dermis | TCA 35%, Jessner's + TCA 35%, glycolic 70% + TCA 35% | 7-10 days | Moderate photoaging, superficial scars |
| Deep | Reticular dermis | Baker-Gordon phenol/croton oil | 10-14 days | Deep rhytides, severe photoaging |

### Superficial Peels (Epidermis Only)

**Glycolic acid (20-70%)**: alpha-hydroxy acid; requires neutralization with sodium bicarbonate; minimal downtime. **Salicylic acid (20-30%)**: beta-hydroxy acid; lipophilic, excellent for acne and oily skin; self-neutralizing. **Jessner's solution**: resorcinol 14g, salicylic acid 14g, lactic acid 14g in ethanol; used alone or as a primer. **Trichloroacetic acid (TCA) 10-25%**: self-neutralizing; excellent for mild photoaging. Require **serial treatments** (4-6 sessions at 2-4 week intervals) for optimal results.

### Medium-Depth Peels (Papillary Dermis)

**TCA 35%**: most commonly used medium-depth agent; endpoint is uniform white frost. **Jessner's + TCA 35%** (Monheit combination): Jessner's solution disrupts epidermal barrier, allowing more uniform TCA penetration. **Glycolic acid 70% + TCA 35%** (Coleman combination): similar synergistic mechanism. **Frosting levels**: level I (erythema with streaky white frost); level II (white frost with erythema showing through); level III (solid white frost, indicates papillary dermis penetration). Ideal for **moderate photoaging**, superficial acne scars, and lentigines.

### Deep Peels (Reticular Dermis)

**Baker-Gordon phenol peel**: 88% phenol 3 mL, tap water 2 mL, liquid soap 8 drops, croton oil 3 drops. **Croton oil** is the primary determinant of peel depth (not phenol concentration). Produces the most dramatic improvement in **deep rhytides** and severe photoaging. Requires **cardiac monitoring** during application: phenol is cardiotoxic and can cause **arrhythmias** (premature ventricular contractions, ventricular tachycardia).

Apply in aesthetic units with **15-minute intervals** between zones to allow hepatic metabolism. Phenol is **hepatotoxic and nephrotoxic**; ensure adequate IV hydration and monitor renal function.

<image>Side-by-side histological cross-section of skin showing the three depths of chemical peel penetration: superficial (epidermal), medium (papillary dermal), and deep (reticular dermal), with labeled skin layers and corresponding peel agents listed</image>

## Adjunctive Resurfacing Modalities

### Dermabrasion

**Mechanical resurfacing** using a high-speed rotary instrument (wire brush or diamond fraise). Operator-dependent depth control based on **visual endpoints**: pinpoint bleeding (papillary dermis), chamois-colored surface (reticular dermis). Excellent for **acne scars**, traumatic tattoos, and rhinophyma. Largely supplanted by laser resurfacing but retains niche indications.

### Laser Resurfacing

**Ablative CO2 laser (10,600 nm)**: vaporizes tissue to precise depths; gold standard for deep resurfacing. **Ablative erbium:YAG (2940 nm)**: 12-18x greater water absorption than CO2; more precise ablation with less thermal damage. **Fractional ablative lasers**: create microscopic treatment zones (MTZs) surrounded by untreated tissue; faster healing with reduced complication risk. **Non-ablative fractional lasers** (1550 nm erbium fiber): stimulate collagen remodeling without epidermal disruption; minimal downtime but less dramatic results.

CO2 laser resurfacing produces **collagen contraction** (immediate tissue tightening of 20-30%) plus long-term neocollagenesis.

### Microneedling

**Controlled micro-injury** using needles (0.5-3.0 mm depth) stimulates collagen production through wound healing cascade. Can be combined with **platelet-rich plasma (PRP)** or topical agents for enhanced delivery. Lower risk of dyspigmentation compared to laser resurfacing; suitable for **darker skin types**. Requires multiple sessions (3-6) spaced 4-6 weeks apart.

<image>Illustration comparing the wound healing patterns of fully ablative laser resurfacing versus fractional ablative resurfacing, showing microscopic treatment zones, thermal damage zones, and surrounding untreated tissue bridges</image>

## Complications

### Early Complications

**Prolonged erythema**: expected after medium/deep peels; concerning if persisting beyond 3 months (may herald scarring). **Herpes simplex reactivation**: can cause widespread vesicular eruption; antiviral prophylaxis is mandatory. **Bacterial infection**: Staphylococcus and Pseudomonas most common; prophylactic antibiotics for deep peels. **Contact dermatitis**: from topical agents used during recovery.

### Late Complications

**Post-inflammatory hyperpigmentation**: most common in Fitzpatrick III-VI; treat with hydroquinone, tretinoin, and strict sun protection. **Hypopigmentation**: more common after deep peels; may be permanent; due to melanocyte destruction. **Scarring**: hypertrophic scars most common in perioral and mandibular regions; treat with silicone sheeting, intralesional steroids. **Demarcation lines**: visible boundary between treated and untreated skin; feathering technique during application minimizes this. **Ectropion**: rare; from excessive skin contraction in the periorbital region after deep peels.

<image>Clinical progression photographs showing the stages of healing after a medium-depth TCA peel: immediate white frost, day 3 desquamation, day 7 re-epithelialization, and 3-month final result with improved skin quality</image>

## Key Clinical Pearls

Depth of peel determines both efficacy and complication risk; always match peel depth to the severity of the condition being treated. Pretreatment with tretinoin and hydroquinone for 4-6 weeks improves outcomes and reduces dyspigmentation risk. Cardiac monitoring is mandatory during Baker-Gordon phenol peels; apply in zones with 15-minute intervals. Fractional technology has dramatically improved the safety profile of laser resurfacing while preserving efficacy. Herpes prophylaxis is non-negotiable for any medium or deep resurfacing procedure.

## References

1. Monheit GD. The Jessner's + TCA peel: a medium-depth chemical peel. *J Dermatol Surg Oncol*. 1989;15(9):945-950.
2. Stuzin JM, Baker TJ, Gordon HL. Treatment of photoaging: facial chemical peeling (phenol and trichloroacetic acid) and dermabrasion. *Clin Plast Surg*. 1993;20(1):9-28.
3. Manstein D, Herron GS, Sink RK, Tanner H, Anderson RR. Fractional photothermolysis: a new concept for cutaneous remodeling using microscopic patterns of thermal injury. *Lasers Surg Med*. 2004;34(5):426-438.
4. Fischer TC, Perosino E, Poli F, et al. Chemical peels in aesthetic dermatology: an update 2009. *J Eur Acad Dermatol Venereol*. 2010;24(3):281-292.