Purpose of the study is to assess the effect and evaluate topographic volume changes of UltraPulse at treating boxcar scars with different energy and the effect of UltraPulse at treating icepick scars.

After being informed about the study and potential risks, all patients giving written informed consent will undergo a 24 hour screening period to determine eligibility for study entry. Upon enrollment, patient who fulfill all the inclusion criteria and does not fulfill any exclusion criteria will be scheduled for their visits.

All subjects will be receiving two sessions of treatment, with the two sessions 8-12 weeks apart. Subjects' face will be divided to left and right, with each side randomized to receive a low versus high energy setting. In the low energy setting side of the face, central base of boxcar scar will be treated with 20mJ, while shoulder of scar will be treated with 50 mJ. In the high energy setting side of the face, central base of boxcar scar will be treated with 30mJ, while shoulder of scar will be treated with 60 mJ. Subject will be blinded regarding which side of the face received low versus high energy setting.

Ultrasound will be used to assess epidermal and dermal thickness change at the treated area. This will be performed before the 1st and 2nd treatment session as well as one month and three month after the 2nd treatment session.

Antera Quantitative 3D Image Analysis will be performed before and after the 1st and 2nd treatment session as well as one month and three month after the 2nd treatment session.

3mm punch biopsy will be taken from 10 volunteers over bilateral face before the 1st treatment session and 3 month after the 2nd treatment session (total of 4 sample will be obtained in each volunteer). Skin specimen will be stained with hematoxylin and eosin as well as relevant stain for collagen and elastic fiber.

Clinical photograph will be taken before and after the 1st and 2nd treatment session as well as one month and three month after the 2nd treatment session. Two blinded board certified dermatologist will be asked to rate the improvement of acne scar by GSAAS according to the clinical photograph taken.

All subjects will be asked to rate their satisfaction regarding treatment response over each side of the face using a 0 to 10 point scale chart.

Inclusion Criteria:

• Subjects have to be aged from 20 to 60 year-old
• Subjects currently have an area of involvement approximately 2cm × 2cm on each side of the face over the temples or cheek bone area
• Classified as mild to moderate acne scar according to global severity of facial acne scar (GSAAS) score
• After evaluation by clinician, those subjects to be treated with "Lumenis"CO2 Laser System (UltraPulse) can benefit from this laser treatment
• Subjects need to be fully functional and aware of the pros and cons of the study. Subject is capable to make self judgement and sign the inform consent under his/her own will
• Others: Have fully understand about this study and is willing to cooperate with the instruction of the study

Exclusion Criteria:

• Those who were known to have keloid formation
• Those who have porphyria or known photosensitivity
• Those who previously underwent laser therapy treatment or skin biopsy and have showed poor result or adverse effect
• Those who were classified as "severe" according to GSAAS system
• Those who have bleeding tendency
• Those who present with clinical data suggesting abnormal platelet function or coagulation disorder (such as prolonged aPTT or PT)
• Those that are currently taking anticoagulants or anti-platelet drugs
• Those who are on aspirin or other NSAIDs
• Those who have history of granulomatous or connective tissue disease
• Female subjects with a positive pregnancy test
• Women who refuse to stay on effective contraception or refuse pregnancy tests during the study
• After evaluation by the clinician, those that have been enrolled in clinical studies over the past 6 months that may alter the current study result
• After evaluation by the clinician, those currently or had previous treatment of atrophic acne scars with fillers, lasers, deep chemical peels, or any other medical or surgical treatment which in the investigators' opinion could alter the results of the current clinical study
• Those that are currently taking photo-sensitive drugs, oral isotretinoin, iron supplement or other herbal medication
• Those that have received laser treatment over the lesion area over the past 3 months
• Those that are currently pregnant or breastfeeding
• After evaluation by the clinician, and concluded underline epilepsy, area to be treated is under infection or ulceration, poor wound healing)