How does laser treatment improve acne scars ?
Fractional lasers create multiple microscopic zones of ablation and heat in the skin to induce collagen remodelling.
An atrophic acne scar corresponds to tissue loss in the dermis. The skin surface then sits lower than the surrounding skin, forming a visible depression.
A fractional laser treats only a fraction of the skin during each session. The treated areas trigger a repair response involving collagen production and reorganisation.
Laser treatment therefore does not directly “fill” a scar : it induces skin remodelling that can reduce its depth and improve its texture.
Which acne scars respond best to laser treatment ?
Superficial or moderately deep atrophic scars generally respond better to laser treatment than very narrow, deep scars.
The three main forms of atrophic scars have different structures. Boxcar scars are round or oval depressions with relatively sharply defined edges. Rolling scars are wider, with gently sloping edges that give the skin an undulating appearance. Ice pick scars have a narrow opening at the surface but extend deeper into the dermis.
These differences in shape and depth directly influence the response to laser treatment.
In a study using a non-ablative fractional laser at 1540 nm, boxcar scars responded better than rolling scars, while ice pick scars showed the weakest response. Another study of an Erbium laser at 1550 nm found the same trend, with a median reduction of 59,2 % in boxcar scars, 40,6 % in rolling scars and 19,1 % in ice pick scars.
The expected result must therefore take the type of scar into account. A person with predominantly ice pick scars cannot expect the same improvement from laser treatment as a person with mainly superficial boxcar scars.
Why do ice pick scars respond less well to laser treatment ?
Ice pick scars respond less well to fractional laser treatment because they are very narrow but extend deep into the skin.
The remodelling achieved with a fractional laser can improve the surrounding skin and sometimes reduce their visibility, but it has difficulty correcting the full depth of the scar on its own.
Techniques targeting the scar directly, continuous ablative laser treatment and medium-deep peeling, are more suitable. Treatment of a face with several types of scars must therefore combine different methods.
The depth of a scar is therefore as important as its surface appearance when choosing treatment.
Is laser treatment effective for rolling scars ?
Yes. Laser treatment can improve rolling scars, but its effectiveness depends particularly on the presence of fibrous adhesions tethering the scar to deeper tissues.
Rolling scars can be connected to deep tissues by fibrous bands. These adhesions pull the skin downwards and create the characteristic depressions responsible for the undulating skin surface.
Laser treatment works mainly by stimulating dermal remodelling, but cannot cut these deep adhesions. When they are substantial, subcision may be necessary to release the skin before laser treatment or in combination with it.
The presence of adhesions therefore explains why laser treatment alone may provide insufficient improvement in certain rolling scars.
Is fractional CO₂ laser treatment effective for acne scars ?
Yes. Fractional CO₂ laser treatment can improve atrophic acne scars and is among the most extensively studied lasers for this indication.
It is an ablative fractional laser that creates multiple microscopic columns of ablation in the skin, separated by areas of intact skin. Healing of these microzones stimulates collagen remodelling and gradually improves the scars.
A recent systematic review of fractional CO₂ laser treatment reports an improvement in scar appearance of between 30 and 70 % in most studies analysed. However, these figures cannot predict individual results because the studies use different protocols, numbers of sessions and assessment methods.
Fractional CO₂ laser treatment causes more significant recovery effects than some non-ablative lasers. Redness, swelling and crusts may appear after the session. Post-inflammatory hyperpigmentation is also possible.
The choice of fractional CO₂ laser treatment therefore depends on the type of scar, the improvement sought and the extent of recovery effects the patient is willing to accept.
Are non-ablative lasers effective for acne scars ?
Yes, non-ablative fractional lasers can also improve atrophic acne scars.
Unlike an ablative laser, they heat microscopic areas of the dermis without removing the skin surface. This action also triggers collagen remodelling.
Non-ablative fractional Erbium lasers, particularly around 1540–1550 nm, have shown effectiveness for atrophic scars, especially certain boxcar and rolling scars.
Their main advantage is generally milder recovery effects than with ablative treatment. In return, several sessions are needed to achieve visible improvement.
How many laser sessions are needed for acne scars ?
Acne scar treatment generally requires 4 to 6 sessions with a non-ablative fractional laser. With an ablative fractional laser, such as CO₂ or Erbium, 3 to 4 sessions may be performed depending on scar depth.
This difference is explained by treatment intensity. Non-ablative fractional laser treatment acts less aggressively at each session and generally requires several successive treatments. Ablative fractional laser treatment induces greater skin remodelling at each session, but also causes more pronounced recovery effects, including redness, crusting and longer recovery time.
The number of sessions also depends on the type and depth of scars. Boxcar, rolling and ice pick scars do not respond to laser treatment in the same way. Superficial scars may require fewer sessions than deep scars.
The number of sessions is therefore adjusted during treatment according to scar characteristics and the improvement achieved after the first sessions.
When can the effectiveness of laser treatment be assessed ?
The result should not be judged in the days following the session because collagen remodelling continues after treatment.
Immediately after laser treatment, the skin may be red, swollen or crusted. These changes reflect treatment recovery effects rather than the final result.
Scar improvement occurs gradually with skin repair and collagen reorganisation. In clinical studies, effectiveness is therefore assessed some time after the sessions rather than immediately after treatment.
Comparing photographs taken too early after laser treatment may lead to its effectiveness being underestimated or overestimated.
Why is it sometimes necessary to combine several acne scar treatments ?
Several treatments may be necessary because acne scars do not all have the same shape, depth or mechanism. A single technique therefore cannot always correct all the scars present on the same face.
A patient may have boxcar, rolling and ice pick scars simultaneously. Some are superficial, others extend deep into the dermis, while certain rolling scars are tethered to deeper tissues by fibrous adhesions.
Treatment must therefore be adapted to each type of scar. A scar tethered to deep tissues may require subcision to release the adhesions. A very deep ice pick scar may require targeted treatment with a medium-deep peel or continuous ablative laser. Fractional laser treatment can then be used to improve skin surface contours and texture more broadly.
The American Academy of Dermatology also states that combining several treatments may be necessary to improve the different types of acne scars.
The aim is therefore not to multiply sessions of a treatment that is ineffective for a particular scar, but to choose, for each scar type, the technique that acts on the mechanism responsible for its appearance.
Who is a good candidate for laser acne scar treatment ?
Laser treatment is particularly useful when a significant proportion of the scars can be improved by remodelling the dermis and skin texture.
Its benefit is generally greater for certain atrophic boxcar and rolling scars than for very deep ice pick scars. The presence of adhesions beneath a rolling scar must also be investigated because laser treatment cannot release them.
Finally, treatment must take skin phototype into account. Darker skin has a greater risk of post-inflammatory hyperpigmentation after certain aggressive treatments, which may require adaptation of the technology and settings.
Laser treatment can therefore improve certain acne scars, but its effectiveness depends above all on scar type, depth, the possible presence of adhesions and skin phototype.
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.
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