Acne scars are the result of inflammation within the dermal layer of skin brought on by acne and are estimated to affect 95% of people with acne vulgaris. The scar is created by an abnormal form of healing following this dermal inflammation. Scarring is most likely to occur with severe nodulocystic acne, but may occur with any form of acne vulgaris.
Atrophic acne scars are the most common type of acne scar and have lost collagen from this healing response. Atrophic scars may be further classified as ice-pick scars, boxcar scars, and rolling scars. Ice pick scars are typically described as narrow (less than 2 mm across), deep scars that extend into the dermis. Rolling scars are wider than ice pick scars (4–5 mm across) and have a wave-like pattern of depth in the skin. Boxcar scars are round or ovoid indented scars with sharp borders and vary in size from 1.5–4 mm across.
Hypertrophic scars are less common and are characterized by increased collagen content after the abnormal healing response. They are described as firm and raised from the skin. Hypertrophic scars remain within the original margins of the wound whereas keloid scars can form scar tissue outside of these borders. Keloid scars from acne usually occur in men and on the trunk of the body rather than the face.
Keloid scars are characterized by smooth hard nodules due to excessive collagen production. They may occur spontaneously or follow skin trauma/surgery, and they are often itchy. Sites of predilection include the shoulders, upper back and chest, ear lobes and the chin.