CO2 laser resurfacing guide: ablative fractional and full-field resurfacing explained

CO2 laser resurfacing uses a 10,600 nm carbon dioxide laser to ablate skin tissue through water chromophore absorption — removing damaged epidermal and dermal tissue and triggering collagen remodeling in the wound-healing response. It remains the gold standard for treating moderate-to-severe photoaging, acne scarring, and skin texture irregularities when downtime is acceptable. Here is a complete guide.

The mechanism: water absorption and tissue ablation

Why 10,600 nm targets skin

The CO2 laser wavelength at 10,600 nm is strongly absorbed by water — and skin tissue is approximately 70% water. This means:
CO2 laser energy is absorbed in the most superficial 20–30 μm of tissue (the water-rich epidermis)
The absorbed energy instantly vaporizes the water in cells → cell destruction → tissue ablation
Each 10,600 nm laser pulse removes a precise depth of tissue determined by the fluence (energy density) and pulse duration

Ablation vs. coagulation zones

Each CO2 laser pulse creates two distinct tissue zones:

Zone of ablation: The superficial tissue vaporized by the laser pulse. For fractional CO2, this is the micro-ablative column (MAC) — a column of vaporized tissue typically 100–200 μm in diameter and 100–1000 μm deep depending on settings.

Zone of coagulation: Surrounding tissue heated but not vaporized — protein denaturation and collagen shrinkage occur. This thermal injury triggers the wound-healing response and collagen remodeling.

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Full-field vs. fractional CO2: the fundamental distinction

Full-field (traditional) CO2 resurfacing

The original CO2 resurfacing technique ablates 100% of the treatment area — every square millimeter of epidermis is vaporized. The entire treatment surface must heal from scratch.

Advantages: Maximum effect per treatment — full-field CO2 is the most powerful resurfacing modality available; significant improvement in severe photoaging and scarring in a single treatment.

Disadvantages:
10–21+ day healing (reepithelialization from wound edges)
Prolonged erythema (3–6 months; can persist to 12 months)
Higher risk of infection (large open wound)
Significant PIH risk, particularly in darker skin types
Permanent hypopigmentation risk in darker skin or with aggressive settings

Current use: Full-field CO2 is still used for severely photodamaged skin, extensive acne scarring, or when maximum effect is required — but fractional CO2 has replaced it for most clinical indications due to the dramatically improved safety profile.

Fractional CO2 resurfacing (Fraxel Re:pair, SmartXide DOT, Lumenis UltraPulse)

*Fractional photothermolysis (Manstein et al., 2004, Seminars in Cutaneous Medicine and Surgery):* The foundational concept: treating only a fraction of the skin surface with each pass — discrete microscopic columns of treated tissue surrounded by untreated, healthy tissue bridges. The healthy bridges provide:
Rapid reepithelialization — cells migrate from surrounding untreated tissue to resurface the ablative columns
Reservoir of intact dermis for fibroblast repopulation
Significantly faster healing and lower complication risk vs. full-field

Fraxel Re:pair (Solta Medical/Bausch Health): The most widely studied fractional ablative CO2 platform. The 10,600 nm fractional beam creates MACs (micro-ablative columns) at variable density (5–70% treatment density) and depth (100–1600 μm).

Treatment density: The percentage of skin surface treated per session. Lower density (10–25%): more conservative, less downtime, multiple sessions needed. Higher density (40–70%): more aggressive single treatment, longer healing but maximum effect per session.

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What CO2 resurfacing treats

Photoaging (the primary indication)

Sun-damaged skin accumulates:
Dyskaryotic keratinocytes → irregular surface texture
Solar elastosis → crosslinked, dysfunctional collagen replacing normal collagen
Pigmentation irregularities (lentigines, poikiloderma)

Fractional CO2 ablates the damaged superficial layers and triggers new collagen synthesis in the dermis — replacing solar elastosis with organized, functional collagen:

Evidence: Walgrave et al. (2012, Lasers in Surgery and Medicine) — significant improvement in rhytid depth, skin texture, and overall photoaging scores after single fractional CO2 treatment (Fraxel Re:pair) in 27 subjects; improvement maintained at 6-month follow-up.

Acne scarring

CO2 resurfacing is among the most effective treatments for atrophic acne scarring (boxcar and rolling scars). The ablative columns destroy fibrotic scar tissue; the collagen remodeling response fills the depressed scar base:

Scar Improvement Scale: Multiple studies document 25–50% improvement in acne scar severity after a single aggressive fractional CO2 treatment session; 50–75% improvement after 2–3 sessions
Combination with subcision (fibrous band release) and filler augments outcome for deep rolling scars

Superficial and mixed pigmentation

CO2 ablation removes the pigmented epidermis in treated columns — effective for:
Solar lentigines (age spots)
Seborrheic keratoses
Epidermal melasma (the dermal component is not addressed by ablation)

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Healing timeline and downtime

The five phases of fractional CO2 healing

Days 0–2 (acute): Immediately post-treatment, the skin appears red, swollen, and the ablative columns produce a bronzed or gridded texture. Significant edema, especially around the eyes. Pain managed with oral analgesics or prescribed pain management.

Days 2–4 (exudate): Crusting over ablative columns; serosanguinous discharge. Soaking and petroleum ointment application is critical — keeping the crust moist accelerates reepithelialization and reduces scar risk. Do not pick crusts.

Days 4–7 (reepithelialization): New epidermis migrates from untreated bridges to resurface ablative columns. By day 5–7 for fractional (low–medium density), the surface is re-epithelialized. Erythema transitions from bright red to pink.

Weeks 1–4 (erythema): Persistent pink-to-red erythema is normal. This is the inflammatory phase — new collagen is forming. Erythema duration correlates with treatment density: conservative fractional = 1–2 weeks; aggressive fractional = 2–4 weeks; full-field = 3–6 months.

Months 1–6 (remodeling): Progressive improvement in skin quality, texture, and pigmentation as new collagen matures. Full results visible at 3–6 months.

Typical social downtime:
Conservative fractional CO2 (10–25% density): 5–7 days
Standard fractional CO2 (30–50% density): 7–10 days
Aggressive fractional CO2 (60–70% density): 10–14 days
Full-field CO2: 14–21 days

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PIH risk: skin type considerations

The critical safety consideration

CO2 resurfacing — both full-field and fractional — carries significant PIH risk in Fitzpatrick types III–VI. The inflammatory healing cascade following ablation triggers a melanocyte response; in skin with more reactive melanocytes, this produces patchy or diffuse darkening.

Risk management:
Fitzpatrick I–II: Low PIH risk; appropriate for standard protocols
Fitzpatrick III: Moderate risk; require conservative settings (lower density, single pass), aggressive SPF during healing, and topical PIH prophylaxis (azelaic acid, kojic acid post-healing, hydroquinone cycles)
Fitzpatrick IV–VI: Significant PIH risk; many providers choose erbium:YAG (less thermal coagulation, less inflammatory response) over CO2; or non-ablative modalities; fractional CO2 can be used by experienced operators at very conservative settings with intensive PIH prophylaxis

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CO2 vs. erbium:YAG vs. non-ablative

| Modality | Wavelength | Mechanism | Downtime | Coagulation | PIH Risk | Best For |
|---|---|---|---|---|---|---|
| CO2 (fractional) | 10,600 nm | Ablation + coagulation | 5–14 days | Significant | Moderate | Photoaging, deep scars |
| Erbium:YAG (fractional) | 2,940 nm | Ablation, minimal coagulation | 3–7 days | Minimal | Lower | Pigmentation, mild scars, darker skin |
| Fraxel Dual (non-ablative) | 1927 nm / 1550 nm | Coagulation, no ablation | 3–5 days | Yes (non-ablative) | Low–moderate | Pigmentation, mild texture |
| IPL | Broad-spectrum | Pigment + vascular | 3–7 days | No | Low | Diffuse photoaging, redness |
| Microneedling RF | RF via needles | Collagen induction | 2–4 days | Focal | Very low | Scars, laxity, all skin types |

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Pre- and post-treatment care

Pre-treatment:
Retinoids stop 1–2 weeks before (sensitize skin; increase healing risk)
Isotretinoin: absolute contraindication within 6–12 months
SPF daily for 4+ weeks pre-treatment (minimize baseline pigmentation)
Antiviral prophylaxis (acyclovir/valacyclovir) — CO2 resurfacing can trigger HSV reactivation; antiviral coverage for 5–7 days perioperatively is standard of care

Post-treatment:
Petroleum ointment (Aquaphor) or prescribed healing ointment applied continuously until reepithelialized
SPF 50+ once healed — mandatory for the full remodeling phase
Retinoids and exfoliants: restart 4–6 weeks post-treatment
Avoid sun exposure during erythema phase

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