Acne scars are formed when there is an influx, or not enough collagen in the spot where the acne is healing. The scar will therefore develop where the original acne was, and where the inflammation occurred. If the scar is raised once healed, then there was too much collagen in the area, whereas a depressed scar (not raised) occurs because of too little collagen during the healing process.
Acne scars can look different on people. There are various types of acne scars, and all have unique characteristics. You can have ice-pick scars, which are deep, narrow, pitted scars, or you can have thick, lumpy scars called keloid scars. On the other hand, some people may have rolling scars, which are broad depressions in the skin, whereas others have what is called boxcar scars which are broad depressions in the skin with sharp edges.
One of the more common types of acne scars are atrophic scars. These types of acne scars are flat, thin, depressed scars that look like acne spots, except they are not raised, bumpy or inflamed.
Depending on the type of acne scarring you have, you will need to treat it differently. For instance, atrophic scars such as boxcar scars, ice pick scars or depressed scars can be lessened over time. The boxcar type responds best to skin resurfacing treatments, whereas the ice pick scars are the most difficult to get rid of.