In the simplest terms, scars form at the site of an injury to tissue. They are the visible reminders of injury and tissue repair.
The occurrence and incidence of scarring is still not well understood. There is considerable variation in scarring between one person and another, indicating that some people are more prone to scarring than others.
Acne scarring frequently results from severe inflammatory nodulocystic acne that occurs deep in the skin, but scarring also may arise from more superficial inflamed lesions. Nevertheless, the only sure method of preventing or limiting the extent of acne scars is to treat acne early in its course, and as long as necessary. The more that inflammation can be prevented or moderated, the more likely it is that scars can be prevented.
The scars caused by increased tissue formation are called keloids or hypertrophic scars. Both hypertrophic and keloid scars are associated with excessive amounts of the cell substance collagen. The excess collagen becomes piled up in fibrous masses, resulting in a characteristic firm, smooth, usually irregularly-shaped scar.