What are the most common side effects after laser treatment on a scar ?
Redness and swelling are the most common reactions after fractional laser treatment. They reflect the inflammatory reaction deliberately induced in the skin to trigger its repair and collagen remodelling.
Depending on the laser and settings used, recovery effects may include :
• Redness of the treated area.
• Swelling, generally more pronounced in the first few hours.
• Temporary post-inflammatory hyperpigmentation.
• A sensation of heat, tingling or burning.
• Peeling.
• Small crusts.
• Increased skin sensitivity during the healing phase.
These effects are not complications. They are part of the expected recovery after many laser treatments when their intensity and duration remain consistent with the treatment performed.
How long does redness last after laser treatment ?
Redness may persist for a few days or longer depending on the type of laser, treatment intensity and the skin's reaction. It is generally less pronounced and shorter-lasting after non-ablative fractional laser treatment than after ablative fractional laser treatment.
Non-ablative fractional lasers usually cause temporary redness with faster recovery. After an ablative fractional laser, such as CO₂ or Erbium, redness is generally more pronounced and may persist longer.
A meta-analysis published in 2026 on acne scar treatment notably found that redness lasted approximately 1,7 days longer after fractional CO₂ or Erbium laser treatment than after fractional microneedle radiofrequency.
The duration of redness also varies according to the energy delivered, treatment density, the area treated and the skin's individual reaction.
Can crusts appear after laser treatment of a scar ?
Yes. Small crusts may appear after certain fractional laser treatments, particularly when treatment is ablative.
An ablative fractional laser creates controlled microzones of skin ablation. Their healing may lead to small crusts or peeling in the days following the session.
Crusts must not be picked off. Removing them prematurely can traumatise the skin as it repairs itself and cause pigmentation changes or abnormal healing.
Recovery effects are generally milder after non-ablative fractional laser treatment, which heats the dermis without ablating the skin surface.
Can laser scar treatment cause brown spots ?
Yes. A laser can cause post-inflammatory hyperpigmentation : the treated area then becomes darker than the surrounding skin following the inflammation caused by treatment.
This risk is particularly significant for darker skin phototypes. A systematic review published in 2026 on complications of facial laser treatments identified post-inflammatory hyperpigmentation as the most frequently reported complication, particularly in phototypes IV to VI.
The risk also depends on the type of laser and treatment intensity. A recent meta-analysis comparing fractional CO₂ laser treatment with conventional microneedling for atrophic acne scars found an approximately threefold higher risk of post-inflammatory hyperpigmentation with fractional CO₂ in the studies analysed.
Sun exposure two months before and two months after the session also increases the risk of pigmentation. Applying sun protection is therefore essential before and after treatment.
Can laser treatment cause white spots or hypopigmentation ?
Yes. Laser treatment can cause hypopigmentation, meaning that the treated area becomes lighter than the surrounding skin.
This complication is less common than redness or hyperpigmentation, but may be more difficult to correct when it persists.
Hypopigmentation occurs when melanin production decreases in the treated area. It may occur particularly when the energy delivered is too high or treatment is too aggressive for the skin being treated.
Can an infection develop after laser treatment on a scar ?
Yes. An infection can develop after laser treatment of a scar, especially after an ablative laser, because the skin barrier is temporarily impaired. However, it is much less common than redness, swelling or crusting.
Pain that increases rather than decreases, spreading redness, discharge or the appearance of unusual lesions should prompt medical advice.
Some facial laser treatments can also reactivate herpes in people with a history of cold sores. This history should be reported before the session so that the risk can be assessed.
Ablative CO₂ and Erbium lasers carry a higher infection risk than non-ablative lasers because they cause greater impairment of the skin barrier.
Can laser treatment worsen a scar or create a new one ?
Yes. A laser that is too aggressive or poorly suited to the type of scar can cause excessive skin injury and worsen an existing scar, or even lead to a new scar. This complication remains rare when treatment is appropriately indicated and settings are adjusted.
The risk must be given particular consideration in people with a history of hypertrophic scars or keloids.
Not all scars can therefore be treated in the same way. A thick scar or keloid is not treated like an atrophic acne scar.
Are the side effects the same with every laser ?
No. Side effects and recovery time vary according to the type of laser used. A fractional CO₂ laser, an ablative Erbium laser and a non-ablative fractional laser do not cause the same recovery effects.
Ablative lasers act more intensely on the skin surface. They generally cause more pronounced redness and crusting, with longer recovery time.
Non-ablative fractional lasers preserve more of the epidermis. Recovery effects are usually milder, but several sessions may be necessary depending on the scar treated.
A recent meta-analysis comparing fractional CO₂ lasers with fractional Erbium lasers for atrophic acne scars accordingly found more pain and longer recovery with fractional CO₂.
The technology used and treatment intensity largely determine the nature and extent of recovery effects.
Who has a greater risk of side effects ?
The risk of side effects increases when the skin has certain risk factors or laser treatment is performed using high settings.
Particular vigilance is required in the following situations :
- Darker skin phototype, because of a greater risk of post-inflammatory hyperpigmentation. Skin phototype is a particularly important factor to consider. Recent evidence shows that pigmentation disorders after laser treatment are more common in phototypes IV to VI.
- Recent sun exposure or tanned skin.
- A history of hypertrophic scars or keloids.
- A history of herpes when treatment involves an area susceptible to reactivation.
- Active infection or inflammation in the area to be treated.
- Use of an ablative laser or high treatment settings.
When should you seek medical advice after laser treatment ?
Redness, swelling and a sensation of heat are common immediately after a laser session. These reactions should gradually subside. Symptoms that develop later or worsen rather than diminish require medical advice.
In particular, contacting the doctor is recommended in the event of :
- Pain that becomes more intense rather than subsiding.
- Redness that spreads or worsens after an initial improvement.
- Discharge or the appearance of lesions that may suggest an infection.
- Significant blistering in the treated area.
- Significant or persistent pigmentation changes.
- Abnormally slow healing.
- The appearance of a raised scar.
These signs should be interpreted according to the type of laser treatment performed and the recovery effects normally expected. Crust formation after certain ablative lasers may, for example, be part of the normal healing process. An area that becomes progressively more painful, redder and more inflamed does, however, require medical assessment.
How can the side effects of laser scar treatment be limited ?
To reduce the risk of side effects after laser treatment, it is essential to adapt the laser to the scar and skin phototype, identify risk factors before the session and carry out the recommended care during healing.
Before treatment, the scar must be examined to analyse its type, depth, surface contours and colour. Skin phototype must also be assessed, along with any history of hyperpigmentation, herpes or abnormal healing.
After the session, care varies depending on the laser used. In particular, the treated area must be protected from the sun and any crusts must fall off spontaneously without being picked off.
The American Academy of Dermatology recommends assessing skin type, scar characteristics and the patient's health before laser treatment to limit the risk of adverse effects.
The most common recovery effects are redness, swelling, a sensation of heat and, with some lasers, crust formation. Hyperpigmentation is a particularly significant risk in darker skin phototypes. Infections, persistent pigmentation disorders and worsening of a scar are rarer and require appropriate medical management.
Article written by Dr Valeria Romano
Dr Valeria Romano supports each patient with a comprehensive approach to the aesthetics of the face, body and intimate areas, and to skin and hair quality. Every treatment is based on a personalised medical assessment.
Learn more about