sentences:  Acne scars are classified based on whether the abnormal healing response following dermal inflammation leads to excess collagen deposition or loss at the site of the acne lesion.Atrophic acne scars have lost collagen from the healing response and are the most common type of acne scar (account for approximately 75% of all acne scars).Ice-pick scars, boxcar scars, and rolling scars are subtypes of atrophic acne scars.