The risks of CO₂ laser: dark marks, infection and what is worth knowing before you decide

CO₂ laser is a medical procedure, not a facial: it vaporises tissue in a controlled way and creates a wound that has to close. That means it has real risks, that most are temporary and that some depend more on who is treated and with what settings than on the machine itself.

This page brings together what is known about those risks, how often they have been described, who is more likely to experience them and which signs should not wait for the next appointment.

This page sets out the safety of fractional CO₂ laser. How a normal recovery progresses — and how that differs from one that has gone wrong — is in recovery day by day.

What is known about the frequency, and what is not

It is worth starting with an honest limitation, because almost no page admits it: there is no reliable figure for the “complication rate of CO₂ laser” that can be given as settled. Studies vary in device, depth, area, skin type and how they record effects.

What can be stated with backing:

• The reference review of complications of fractional resurfacing, which searched the literature from 1998 to 2009, concludes that complications span the full range of severity and can be long-lasting, and that although the overall rate is much lower than with traditional ablative techniques, serious complications can develop.
• The most-cited clinical series assessed 961 consecutive treatments in skin types I to V. Seventy-three treatments (7.6%) developed complications. The most frequent were acneiform eruptions (1.87%) and herpes simplex outbreaks (1.77%). The effects were spread evenly across ages, skin types, sites and settings with one exception: post-inflammatory hyperpigmentation, more frequent in darker skin types. The authors stress that they were temporary and left no serious sequelae such as scarring.

One important qualification for reading that 7.6% properly: that series was carried out with a 1,550 nm non-ablative fractional laser, not with CO₂. It is useful for understanding the pattern of complications of a fractional treatment and the weight of skin type, not for putting a number on CO₂, which is ablative and works deeper.

Post-inflammatory hyperpigmentation

It is the adverse effect that most shapes the indication in Mediterranean skin.

It consists of the treated area responding to inflammation by producing more pigment, so that a darkening appears where there was none. It is usually temporary, but it can last months, and it is more likely the higher the skin type, the more recent the sun exposure and the poorer the sun protection afterwards.

Three things worth being clear about:

• It is not a burn and not necessarily a mistake. It is a predictable response of certain skin to a controlled injury, which is why it is anticipated before treating.
• It is the real reason summer is a bad time. Skin that is already tanned and foreseeable exposure afterwards multiply the risk.
• Sun protection afterwards is treatment, not advice. The published recommendation is to maintain protection and sun avoidance throughout the period of redness, precisely in order to minimise it.

Late hypopigmentation

It is the opposite and it is worse news: the treated area is left lighter than the skin around it. It is less frequent than hyperpigmentation and considerably harder to correct, and it can appear some time after treatment. It is one of the reasons the depth of treatment is not increased “just in case”.

Infection and reactivation of herpes

Treated skin is an open surface until it closes, so it can become infected.

• Herpes simplex. It is the most characteristic reactivation in facial resurfacing: in the series of 961 treatments it appeared in 1.77%. In patients with a history of cold sores, antiviral prophylaxis is prescribed, which in the ablative resurfacing literature is started the day before and maintained until epithelialisation is complete, at around ten days. The specific regimen is set by the treating doctor.
• Acneiform eruptions. These were the most frequent complication in that series (1.87%). They are a nuisance and they are temporary.
• Bacterial infection. Less frequent, and it is what justifies the warning signs: discharge, a bad smell, fever or pain that increases instead of easing.

Scarring

It is uncommon and it is the complication that worries people most, with reason. It appears above all with aggressive settings and in areas of thin skin, and in the series of 961 non-ablative fractional treatments none was recorded.

This is where patient selection counts for more than anything else: a history of keloid or hypertrophic scarring requires a specific assessment before anything is considered.

Redness that does not go away

Prolonged erythema beyond what would be expected is itself a described adverse effect. It should be distinguished from the normal redness after treatment, which eases progressively. The sign that matters is not that it is red, but that it stops improving or gets worse.

Who is at greater risk

The reference review sums it up in three factors, and they are what is reviewed in consultation before anything is recommended:

• Sensitive areas of skin. The eyelid, the neck and the chest are not the cheek: the skin is thinner and the margin is smaller.
• Intrinsically darker skin types. Not an absolute contraindication, but it changes the settings, the preparation and the conversation.
• Predisposing medical factors. A history of herpes or of keloid, active infection, concurrent treatments and a realistic ability to follow the aftercare.

To those are added the ones that depend on timing: a tan or foreseeable sun exposure, and pigmented lesions that have not been diagnosed beforehand. A mark that has changed, bleeds or itches is investigated; it is not treated with a laser. It is set out in the assessment of skin lesions.

Warning signs

Get in touch without waiting for your scheduled appointment if you develop:

• pain that increases rather than eases;
• discharge or a bad smell;
• fever;
• clustered blisters;
• an area that is clearly behaving differently from the rest;
• redness that intensifies after the first few weeks.

What actually reduces the risk

It is not the products: it is the decisions taken beforehand.

1. Examining the skin and establishing the skin type before deciding on depth and density.
2. Choosing the time of year, and postponing if there is a tan or foreseeable exposure.
3. Ruling out undiagnosed pigmented lesions in the area to be treated.
4. Prescribing antiviral prophylaxis where there is a history of herpes.
5. Matching the settings to the aim, rather than treating deeper to reduce the number of sessions.
6. Following the sun protection throughout the period of redness.
7. Asking what equipment will be used and who operates it. It is reasonable and no serious centre takes offence.

The reference review says it plainly: many of these complications are potentially preventable. That sentence is, in effect, the whole argument of this page.

Frequently asked questions

Can CO₂ laser leave marks?

Yes. Post-inflammatory hyperpigmentation is the adverse effect that most shapes the indication, it is more likely in darker skin types and with sun exposure, and it is usually temporary although it can last months.

What is the likelihood of something going wrong?

There is no reliable figure specific to CO₂. In a series of 961 treatments with a non-ablative fractional laser, 7.6% developed some complication, all temporary. With CO₂, which is ablative and works deeper, the risk profile is different and depends a great deal on the settings.

Can it leave a scar?

It is uncommon but possible, particularly with aggressive settings or in areas of thin skin. A history of keloid or hypertrophic scarring requires a specific assessment.

I get recurrent cold sores — can I be treated?

It can usually be considered with antiviral prophylaxis. In the resurfacing literature, the antiviral is started before treatment and maintained until the skin has closed. The regimen is set by the doctor.

Is it more dangerous if I have darker skin?

A darker skin type does not rule out treatment, but it does increase the risk of post-inflammatory hyperpigmentation and means lowering the settings, being especially careful with preparation and being cautious about expectations.

A lighter patch has appeared — will it go?

Hypopigmentation is less frequent than a dark mark and considerably harder to correct. It should be assessed by whoever treated you.

When do I need to call the clinic?

With increasing pain, discharge, a bad smell, fever, clustered blisters or an area behaving differently from the rest. Do not wait for your appointment.

Can moles or marks be treated with CO₂ laser?

A pigmented lesion that has not been diagnosed is not treated with a laser. If it has changed, bleeds or itches, it is investigated first.

Sources

• Metelitsa AI, Alster TS. Fractionated laser skin resurfacing treatment complications: a review. Dermatol Surg. 2010;36(3):299-306. A MEDLINE review 1998–2009: complications span the full range of severity, are more likely in sensitive areas, darker skin types and with medical risk factors, and many are potentially preventable. https://pubmed.ncbi.nlm.nih.gov/20100273/
• Graber EM, Tanzi EL, Alster TS. Side effects and complications of fractional laser photothermolysis: experience with 961 treatments. Dermatol Surg. 2008;34(3):301-305. A series of 961 treatments with a 1,550 nm non-ablative fractional laser in skin types I–V: 7.6% complications; acneiform 1.87%; herpes simplex 1.77%; post-inflammatory hyperpigmentation more frequent in darker skin types. https://pubmed.ncbi.nlm.nih.gov/18190541/
• Batra RS. Ablative laser resurfacing — postoperative care. Skin Therapy Lett. 2004;9(7):6-9. Antiviral prophylaxis from 24 hours before until epithelialisation is complete; sun protection throughout the period of erythema to minimise post-inflammatory hyperpigmentation. https://pubmed.ncbi.nlm.nih.gov/15334277/
• Delker S, Livingstone E, Schimming T, Schadendorf D, Griewank KG. Melanoma diagnosed in lesions previously treated by laser therapy. J Dermatol. 2017;44(1):23-28. In 9 of 11 cases (82%) no histological examination had been carried out before the laser. https://pubmed.ncbi.nlm.nih.gov/27345456/

Book your consultation

If you are considering a CO₂ laser and want to know what risk it carries for your skin — not in general — that is what an in-person assessment determines: skin type, history, area and time of year change the answer completely, and sometimes the conclusion is to wait or to consider something else.

Clinical confirmation by the surgeon

Dr Enrique Salmerón González

Specialist in Plastic, Aesthetic and Reconstructive Surgery
Registration no. 46/4624077

Dr Elena García Vilariño

Specialist in Plastic, Aesthetic and Reconstructive Surgery
Registration no. 46/4624503

Last reviewed: 23 August 2026. This content is for information only and does not replace an individual assessment by a healthcare professional.