CO2 Laser vs Fractional CO2: Same Wavelength, Very Different Treatments

If you have ever left a consultation unsure whether you were being offered a “CO2 laser” or a “fractional CO2 laser,” the terminology is genuinely confusing.

Both use CO2 laser energy at approximately 10,600 nm. What changes is how that energy is delivered.

Traditional fully ablative CO2 resurfacing treats essentially the entire surface of the selected area. Ablative fractional CO2 creates thousands of microscopic treatment columns separated by untreated skin.

Some laser platforms can deliver more than one treatment pattern; others cannot. So knowing that a clinic owns a “CO2 laser” does not tell you what procedure you are actually being offered.

The difference matters because treatment depth, recovery time and risk can be very different.

What a CO2 laser actually does

CO2 resurfacing does two things at once: it removes tissue and creates controlled heating in the tissue immediately around it. Both contribute to the wound-healing response.

Water is the target

CO2 laser light at 10,600 nm is strongly absorbed by water, the principal chromophore in skin for this wavelength.

At sufficient energy, rapid heating of tissue water causes vaporisation and tissue ablation. But ablation is not the whole effect.

CO2 treatment also produces thermal coagulation in tissue immediately surrounding the ablated area. Histological studies of ablative fractional CO2 show microscopic cavities surrounded by zones of coagulated tissue.

That combination of ablation and controlled thermal injury initiates wound healing and dermal remodelling. Collagen changes continue after the procedure, which is why the final result cannot be judged immediately.

So “ablative” does mean that tissue is physically removed. It does not mean that the surrounding tissue receives no heat.

From laser scalpel to skin resurfacing

The CO2 laser dates to 1964. Modern skin resurfacing came decades later, after engineers learned to deliver its energy in much shorter pulses and controlled scanning patterns.

The CO2 laser was first developed in 1964 by Patel and colleagues at Bell Laboratories.

Its strong absorption by water quickly made it useful as a surgical laser. Depending on how the beam was focused and delivered, CO2 energy could be used to incise, vaporise or coagulate soft tissue, with coagulation also providing haemostasis.

Its role in cosmetic skin resurfacing developed later.

In the early 1990s, pulsed CO2 systems and computerised scanners represented an important technological shift. Shorter, high-energy pulses allowed tissue to be ablated with less unwanted heat accumulation and charring than older continuous-wave approaches.

By the mid-1990s, pulsed CO2 resurfacing was being studied extensively for facial wrinkles and photodamage. A 1996 clinical study of 259 patients treated facial rhytides with a high-energy pulsed CO2 laser. The results were substantial, but so was the recovery: erythema lasted one to three months in that study, and transient hyperpigmentation occurred in 30% of patients.

That combination — impressive resurfacing with considerable wound healing and downtime — helps explain what happened next.

Rather than abandoning CO2 ablation, researchers began looking for ways to treat only a fraction of the skin surface at a time.

Fully ablative CO2 resurfacing

Traditional fully ablative, or full-field, CO2 resurfacing treats essentially the entire surface within the selected treatment area rather than leaving microscopic islands of untreated epidermis between treatment zones.

Modern pulsed and scanned CO2 systems made it possible to control thermal injury far more precisely than earlier continuous-wave systems. Fully ablative resurfacing subsequently became an important treatment for severe photodamage, wrinkles and scarring.

It can produce substantial improvement, but recovery and complication risks are also substantial.

Published full-face CO2 studies have reported re-epithelialisation at approximately 7–10 days, while erythema may persist for weeks and sometimes considerably longer.

Anaesthesia depends on treatment area, depth and clinical practice. Techniques include local and regional anaesthesia, nerve blocks, intravenous sedation and general anaesthesia. Full-face treatment does not automatically mean general anaesthesia, but it is clearly a different undertaking from a light fractional procedure performed with topical anaesthetic alone.

Recognised complications include prolonged erythema, infection, scarring, hyperpigmentation and delayed hypopigmentation. Persistent hypopigmentation and visible lines of demarcation are particularly important historical complications of aggressive fully ablative resurfacing.

Fully ablative CO2 has not disappeared, but fractional resurfacing provided a way to preserve part of its ablative effect while reducing the amount of skin wounded at one time.

Fractional photothermolysis: the idea came before fractional CO2

Fractional resurfacing did not begin with CO2. The fractional concept was demonstrated first with non-ablative lasers; ablative fractional CO2 came afterward.

Fractional photothermolysis was introduced by Dieter Manstein and colleagues in 2004.

The original study did not use a CO2 laser. It used prototype devices emitting at approximately 1.5 µm and created microscopic thermal treatment zones in the skin while leaving intervening tissue untreated.

That distinction matters.

The 2004 paper established the fractional concept. Ablative fractional CO2 followed later. In 2007, Hantash and colleagues described a prototype 10.6-µm CO2 system that produced microscopic zones of ablation surrounded by coagulation while leaving viable tissue between them.

The basic historical sequence is therefore:

• 1964: CO2 laser developed.
• Early 1990s: pulsed and scanned CO2 systems advance full-field skin resurfacing.
• 2004: fractional photothermolysis demonstrated with non-ablative 1.5-µm devices.
• 2007: published histological characterisation of ablative fractional CO2 resurfacing.

Fractional photothermolysis and fractional CO2 belong to the same technological story. They are not the same treatment.

“Fractional” does not mean “non-ablative”

“Fractional” describes the treatment pattern. It does not tell you whether tissue is removed. Fractional CO2 is an ablative fractional treatment.

This is one of the most important distinctions for patients.

Fractional describes the spatial pattern of treatment. It does not tell you whether tissue is removed.

An ablative fractional CO2 laser uses 10,600-nm CO2 energy to create microscopic ablation channels surrounded by thermal coagulation.

A non-ablative fractional laser, such as many 1,550-nm erbium-glass systems, creates columns of thermal injury without ablating comparable channels through the skin surface.

Both can truthfully be described as “fractional laser.” Their mechanism, recovery and risk are not the same.

A useful way to decode the terminology is:

• CO2 tells you the laser wavelength.
• Fractional tells you the treatment pattern.
• Ablative tells you that tissue is removed.

For ordinary clinical use, “fractional CO2” generally refers to an ablative fractional treatment.

Brand names can make this even more confusing.
Fraxel is a good example. Published studies describe Fraxel 1550-nm and 1927-nm systems as non-ablative fractional lasers, while Fraxel re is a 10,600-nm ablative fractional CO2 laser.
So being told that a treatment is “Fraxel” does not, by itself, tell you whether it is ablative, non-ablative or even CO2. The exact device and wavelength matter.

Energy and density matter — but they are not the whole treatment

There is no universally “best” fractional CO2 setting. The appropriate balance between depth, coverage, effect and risk depends on what is being treated and on the individual patient.

Fractional CO2 devices allow clinicians to alter several parameters.

Energy delivered to each microscopic treatment zone influences the depth and dimensions of injury. Density determines how much of the surface is treated during a pass. Pulse characteristics, spot size, stacking and the number of passes also matter.

There is no universal rule that “more aggressive” equals “better.”

In a randomized comparison of fractional CO2 settings for atrophic acne scars, lower-fluence and lower-density treatment produced significant improvement with fewer adverse effects, while higher fluences and densities produced more evident adverse effects.

But that cannot be converted into “lower is always better.”

A retrospective study of 121 acne-scar patients found an association between higher energy and greater improvement, although the estimate was very imprecise. Another 82-patient Asian cohort found outcome related to the number of treatment sessions rather than energy.

And in a 2025 randomized split-face trial of static periorbital wrinkles in Chinese patients, low energy combined with higher-density coverage performed best among the tested strategies.

The defensible conclusion is simpler: optimal parameters depend on the indication, target depth, anatomical area, skin and device. A single rule about energy or density cannot be applied to every fractional CO2 treatment.

Fractional CO2 temporarily changes the skin barrier

For several hours after ablative fractional CO2, the skin can be measurably more permeable. What is applied during that period matters.

Ablative fractional CO2 creates microscopic channels through the skin, which can markedly increase penetration of substances applied afterwards.

This phenomenon has developed into the field of laser-assisted drug delivery.

The dimensions of the channels are highly parameter-dependent. In one experimental fractional CO2 study, channels were approximately 300 µm wide and reached about 1.85 mm deep, surrounded by a thin coagulation zone. Those dimensions belong to that experimental configuration; they are not a standard depth for fractional CO2 treatment.

Human research also shows that the barrier does not recover instantly.

In one study using a 10,600-nm fractional CO2 laser, uptake of a test molecule remained significantly enhanced for up to six hours. Optical coherence tomography showed that most channels were open immediately after treatment, progressively closed with time, and were almost entirely closed by 24–48 hours.

This does not mean that every ingredient applied afterwards will penetrate to the same extent. Penetration depends on the molecule, formulation and laser parameters.

It does mean that post-treatment skincare should be treated as part of the medical procedure rather than improvised at home.

What does fractional CO2 actually work for?

Atrophic acne scars

Fractional CO2 is a well-established treatment for atrophic acne scars, but the literature does not support the idea that it is uniquely superior to every alternative.

A retrospective study of 121 patients found moderate-to-excellent improvement in 50.4% after the first treatment session. Rolling scars were associated with greater odds of improvement than ice-pick scars, but the confidence interval around that estimate was wide.

A 2024 systematic review and meta-analysis of eight studies involving 418 patients found fractional CO2 more effective than fractional Er for atrophic acne scars, although CO2 also tended to cause more pain and may carry greater risk of post-treatment pigmentation.

An earlier 2021 meta-analysis found no significant difference between fractional CO2 and pooled non-CO2 laser therapies on several efficacy outcomes.

Those findings are not necessarily contradictory: the comparator treatments and study designs differed.

The reasonable conclusion is that fractional CO2 is an effective acne-scar treatment with a substantial evidence base, but treatment choice still depends on scar type, skin, acceptable downtime and the alternatives being compared.

Treatment interval is also less settled than many protocols imply. A randomized intra-individual trial involving only 13 patients found similar results when two sessions were spaced one month or three months apart. Because the study was very small, it should not be treated as proof that interval never matters.

Photoaging and wrinkles

Fractional CO2 has clinical evidence supporting improvement in photoaging and wrinkles.

A 2025 randomized split-face study in Chinese patients found improvement in static periorbital wrinkles after fractional CO2 treatment, with an overall efficacy rate of 68.2% by both investigator and patient assessment.

Long-term evidence exists but is much smaller.

In one study, 56 Asian patients underwent a single full-face fractional CO2 treatment for photoaging. Thirty were available for five-year follow-up, and photoaging scores remained significantly improved compared with baseline.

That is encouraging durability data. It is not the same as evidence from a large controlled five-year trial, because only 30 treated patients were followed long term and there was no untreated control group.

Pigment change: the numbers vary enormously

PIH is important enough to discuss seriously, but published rates vary too widely to turn a skin type into one honest percentage of individual risk.

Post-inflammatory hyperpigmentation is one of the most important adverse effects to discuss before CO2 resurfacing.

There is no single reliable percentage that can be applied to every patient.

In one study of ablative fractional CO2 for acne scars in Asian patients, mild PIH developed in 92% of subjects, corresponding to 51% of treatment sessions.

That figure is real. It is not a general “92% risk for Fitzpatrick IV+ skin.”

A different retrospective study of 82 Asian patients with Fitzpatrick III–IV skin treated for atrophic acne scars found PIH in 60 patients, or 73.17%. In 26 patients — 31.71% of the full cohort — pigmentation persisted for longer than three months.

The same study recorded:

• erythema in all patients, persisting beyond three months in 19.51%;
• acne flare in 9.76%;
• new post-laser scarring in 2.44%;
• hypopigmentation in 1.22%.

A review of prospective CO2 studies found PIH rates ranging from 0% to 100% and did not find convincing evidence that Fitzpatrick phototype alone independently predicted its occurrence. The literature was heterogeneous and inadequately powered for a definitive risk model.

That does not mean skin colour is irrelevant clinically. It means phototype alone cannot provide an honest individual percentage.

Laser parameters, indication, inflammatory response, sun exposure and aftercare can all contribute.

Hypopigmentation is a different problem

Hyperpigmentation and hypopigmentation should not be treated as opposite versions of the same complication.

Post-inflammatory hyperpigmentation often improves with time. Delayed hypopigmentation after aggressive CO2 resurfacing can be persistent and difficult to treat.

Its mechanism should not be simplified to “the laser destroyed the melanocytes and they never returned.”

Histological evidence from delayed hypopigmentation after CO2 resurfacing has demonstrated decreased epidermal melanin without a corresponding reduction in melanocyte number. That means permanent melanocyte destruction is not an adequate universal explanation.

Persistent pigment loss remains a recognised complication, particularly of more aggressive resurfacing.

Infection and herpes reactivation

CO2 laser treatment does not sterilise the treated skin.

Infection is a recognised complication after resurfacing, and herpes simplex reactivation is particularly important during facial treatment because an outbreak can interfere with healing and potentially contribute to scarring.

Antiviral prophylaxis is therefore commonly used for facial ablative resurfacing.

One randomized clinical trial found valacyclovir effective for HSV-1 prophylaxis using 500 mg twice daily for 14 days, whether started the day before treatment or on the morning of treatment.

That is a studied regimen, not a prescription for every patient. The exact prophylaxis should be determined by the treating clinician.

Isotretinoin: the old blanket waiting rule is no longer supported

The traditional 6–12 month waiting rule should not be applied indiscriminately to fractional laser procedures. Fully ablative resurfacing is a separate question.

The traditional teaching was to avoid resurfacing procedures for six to twelve months after systemic isotretinoin because of concerns about abnormal scarring and delayed healing.

A 2017 systematic review and expert consensus examined 32 publications covering 1,485 procedures.

The authors found insufficient evidence to support delaying fractional ablative or fractional non-ablative laser procedures solely because a patient was currently taking or had recently completed isotretinoin.

That conclusion does not extend automatically to every resurfacing procedure.

The same review did not recommend mechanical dermabrasion or fully ablative laser resurfacing during systemic isotretinoin treatment.

So the modern evidence does not support one universal “six-to-twelve-month rule” across fully ablative CO2, fractional CO2 and non-ablative fractional lasers. They need to be considered separately.

Who needs particular caution?

Candidate selection matters as much as the machine.

Active infection in the treatment area — particularly active herpes — is a clear reason to postpone resurfacing.

A history of poor wound healing, abnormal scarring, previous radiation in the treatment area, significant pigmentary problems or an inflammatory skin disease may alter the risk and warrants individual assessment.

Psoriasis or vitiligo should not simply be converted into an internet checklist saying “CO2 contraindicated.” Trauma can provoke Koebnerisation in susceptible disease, but fractional CO2 has also been investigated therapeutically in some of these conditions.

Similarly, previous burns are not a blanket contraindication: fractional CO2 is used in scar treatment, including burn scars.

The relevant question is whether the particular skin being treated can heal safely.

What recovery actually looks like

There is no single “CO2 laser downtime.” Fully ablative and fractional CO2 create different wounds, and even fractional recovery changes substantially with treatment intensity.

The first question is which CO2 procedure you are having.

Fully ablative CO2

Full-field resurfacing produces a continuous wound across the treated surface.

Complete re-epithelialisation typically occurs within approximately 7–10 days. Erythema can persist for several weeks and sometimes substantially longer.

This is not a “weekend treatment.”

Ablative fractional CO2

Fractional treatment leaves intervening skin untreated, allowing more rapid repair.

Recovery varies considerably with energy, density, passes and anatomical site. Crusting, erythema and oedema for several days are common, but aggressive fractional treatment can have considerably more downtime than a light fractional session.

A clinic therefore should not quote “fractional CO2 downtime” without also telling you what treatment intensity it intends to use.

Wound-care protocols also vary. Studies have used petrolatum-based care, hydrogels and closed dressings for different durations. There is not one evidence-based rule that every dressing must be removed after exactly 48 hours.

Sun avoidance and photoprotection matter because post-treatment inflammation can contribute to pigmentation. A small randomized study in Asian patients found lower early pigmentation when broad-spectrum sunscreen with anti-inflammatory ingredients was introduced from the first day after ablative fractional CO2, although the finding belongs to that specific protocol and product strategy.

Follow the post-treatment products and timing prescribed for the procedure you actually received.

Questions worth asking before you book

1. Is this fully ablative CO2 or ablative fractional CO2?
2. What energy, density and number of passes are you planning, and why?
3. How much downtime do you expect with those particular settings?
4. What is my individual risk of hyperpigmentation or hypopigmentation?
5. What is your protocol if I have a history of herpes simplex?
6. Exactly what should I apply during the first days after treatment?
7. How many sessions are you expecting and why?
8. If I currently take or recently stopped isotretinoin, how does that change your plan?

The essentials

• CO2 laser light is approximately 10,600 nm and is strongly absorbed by water.
• The CO2 laser was developed in 1964; pulsed and scanned systems later enabled much more controlled skin resurfacing.
• Fully ablative CO2 treats essentially the complete surface within the selected area.
• Ablative fractional CO2 creates microscopic ablation zones separated by untreated skin.
• Fractional photothermolysis was introduced in 2004 with non-ablative 1.5-µm devices. Published ablative fractional CO2 work followed.
• “Fractional” describes a treatment pattern. It does not mean non-ablative.
• Energy and density matter, but there is no universal setting that is best for every indication or patient.
• Fractional CO2 has good evidence for atrophic acne scars and clinical evidence for photoaging and wrinkles, but it is not uniquely superior to every alternative.
• PIH rates vary dramatically between studies. A single percentage cannot reliably predict an individual patient's risk.
• Hypopigmentation can be persistent, and its mechanism is more complicated than simple permanent destruction of melanocytes.
• Ablative fractional CO2 temporarily disrupts the skin barrier, which is why early post-treatment products matter.
• Infection and HSV reactivation remain recognised complications; CO2 treatment does not sterilise the skin.
• Current evidence does not support applying the old 6–12 month isotretinoin waiting rule indiscriminately to fractional laser procedures.
• Recovery estimates must distinguish fully ablative from fractional ablative CO2.