Causes of Acne Scars
When a 
tissue suffers some kind of damage, the body rushes to repair the injury site. Among the elements that repair the damaged tissue are white blood cells and an array of inflammatory molecules that repair tissue and fight infection. However, when their job is done they may leave a somewhat messy repair scar, because they don’t care about aesthetics or anything like that.
In the case of acne scars, the injury is caused by the body’s inflammatory response to sebum, bacteria and dead cells in the plugged sebaceous follicle. Two types of true scars exist: depressed areas such as ice-pick scars, and raised thickened tissue such as keloids.
White blood cells and inflammatory molecules may remain at the site of an active acne lesion for days or even weeks. In people who are susceptible to scarring, the result may be acne scars. There is considerable variation in scarring between one person and another, indicating that some people are more prone to scarring than others. Scarring frequently results from severe inflammatory nodulocystic acne that occurs deep in the skin. But, scarring also may occur from more superficial inflamed lesions.
The life history of acne scars also is not well understood. Some people bear their acne scars for a lifetime with little change in the scars, but in other people the skin undergoes some degree of remodeling and acne scars diminish in size.
