Depressed acne scars like rolling/box scars cannot be removed completely. Depending on each individual assessment, it may take 3 or up to 6 sessions of fractional lasers to substantially improve them.
I would go for a clinic that uses different modalities and combination treatments to treat acne scarring as that is proven to improve it faster (in fewer sessions). It helps also to stick with a doctor and a treatment plan that you trust and makes sense, since you may see less results at the start (acne scar treatments rely a lot on collagen regeneration which takes time).
Hope this helps!
