How many CO2 laser sessions do acne scars need?
Most patients require a test patch followed by one to two sessions of fractional CO2 laser, assessed at least three months apart. Where two sessions have produced no improvement at all, further sessions are usually not helpful.
The test patch comes first because the healing response to resurfacing varies between individuals, and treating a small area demonstrates how a particular patient's skin behaves before committing to a full face. It also identifies those at higher risk of pigmentary change, which is a complication far better avoided than discovered.
Fractional resurfacing works on the surface of the skin. It improves shallow boxcar scars, general surface irregularity and texture, and it evens out the changes left behind by earlier procedures. It does not correct scars tethered to deeper tissue, it does not reach the base of a narrow ice pick scar, and it does not replace lost volume. These are the three commonest reasons that a course of laser treatment disappoints.
Consequently, where two properly performed sessions have achieved nothing, repeating the same treatment tends to produce more of the same. The useful question is not how many further sessions are required but what types of scar are actually present. Tethered rolling scars require subcision first, and narrow deep scars require TCA CROSS or punch excision. Once the contour has been addressed the laser has something useful to do, and frequently works considerably better than it did previously.
Three months is the minimum period before assessing a result, since new collagen forms over three to six months and remodelling continues for up to a year. Photographs taken in identical lighting are more reliable than memory, as the change is gradual and easily missed. Before arranging a third session I would generally advise reassessment of the scar types present, since where these prove to be tethered or too deep for resurfacing the money is considerably better spent on the procedure that addresses them.
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