Atrophic scars (pronounced aye TRO fick) form a depression or sunken area because of damage to the collagen, fat or other tissues below the skin. These scars are caused by: Acne, chickenpox, surgery and accidents.
Keloid and hypertrophic scars
Keloid and hypertrophic scars are dense, raised scars that are thicker than surrounding skin. They occur when the body produces too much collagen while a wound heals. They can be removed by surgery, but might return.