CO2 laser resurfacing vaporizes tissue at a depth of 20 to 60um and zones of thermal necrosis ranging another 20 to 50um.31 Energy at 10.600nm wavelength is absorbed by both intracellular and extracellular water, causing rapid heating and vaporization of tissue.32–34 Dermal heating below the zone of ablation induces a wound-healing response,32,35 which causes collagen remodeling and heat-mediated tissue contraction. Re-epithelialization generally takes 5 to 10 days, and erythema may persist for months.32 Side effects may include dyschromia (hyper- or hypopigmentation),9,32,36 infection,37,38 lines of demarcation between treated and untreated areas,32 and scarring.36–38

Pinpoint irradiation technique. Pinpoint irradiation technique accompanied by needling is as effective as FP in the treatment of atrophic acne scars.53,58 It often induces microscopic thermal wounds to achieve skin rejuvenation treatment for ice pick acne scars. In pinpointed irradiation, no complications could be seen as those with ordinary laser resurfacing and the downtime is shortened to 3 to 6 days. All irradiated points on the face were small dry macules of ablated epithelium, which could be gently removed with a topical antibiotic cream after a day. The color of the treated scar area was back to pink or normal within 2 to 4 days. Also, postoperative hyperpigmentation did not occur;58 this could be because there was no overlapped irradiation, no massive damage, and the time interval between each shot was relatively long.53

The CROSS technique entails stretching the skin and using a fine wooden toothpick to apply 65 to 100 percent TCA to the bottom of the ice pick scar, which leads to destruction of the epithelial tract. This is followed by collagenization in the healing phase and filling up of the depressed ice pick scar. It causes momentary, mild, tolerable burning on application, and no anesthesia is required. Collagen formation may take 2 to 3 weeks and can continue up to 4 to 6 weeks. On average, about 25 percent improvement of scars takes place with one session. The procedure may be repeated two or three times at intervals of 2 to 4 weeks.17 The advantage of the CROSS technique is that since the adjacent normal tissue and adnexal structures are spared, healing is more rapid with a lower complication rate.17,25,26

If multiple procedures were combined, then many types of scars and fine textural irregularities would likely be improved to a degree that could not be obtained by each procedure alone. The varying morphology of acne scars, especially when multiple types of scars are found in the same patient, suggests the need for combination therapy to provide the most effective treatment. Stem cell therapy might have the potential as a promising therapy for atrophic acne scars in the future.