These are flat, red spots where an acne lesion was once located. They can persist for a number of weeks and then fade on their own.
Sometimes a healed acne scar leaves discolored skin, which is also called post-inflammatory hyper-pigmentation. Skin discoloration can remain visible for months after an acne lesion has healed.
Some types of acne can leave scars that appear as enlarged, raised growths of tissue. These acne scars may be called keloids or hypertrophic scars, and are caused by excess production of collagen in your skin.
More common than raised tissue scars are the acne scars that are caused by a loss of tissue. These acne scars are called icepick scars, depressed fibrotic scars, soft scars, atrophic macules, or follicle macular atrophy. They tend to appear sunken and look like pits in the skin.