Facial resurfacing is usually done with an ablative laser (e.g., CO2 laser). Ablative means that the laser is removing some of your skin. By contrast, non-ablative lasers do not remove skin. Instead, they heat up fibroblasts and stimulate them to thicken the underlying collagen — in essence treating wrinkles from the inside out. Ablative lasers are more damaging and invasive than non-ablative lasers. Another difference is that non-ablative lasers require multiple treatments, while ablative lasers usually require just one.
source : facialplasticsurgery