There is a fluent transition between blemished skin and acne. Generally speaking, what is meant by acne is acne vulgaris or simplex, which represents the most common forms of acne that appear from puberty on, especially on one's face and back. Acne vulgaris can be divided into degrees of severity according to the visible sypmtoms:

• Acne vulgaris comedonica ("blackheads")
• Acne vulgaris papulo-pustulosa, which occurs when bacteria colonize the comedo and cause secondary inflammation around the comedo, forming papules and pustules.
• Acne vulgaris conglobata, in which painful nodules and abscesses with fistulae appear in the face and upper part of the body, and often leave scars after healing.                                       

Various combinations of these symptoms are of frequent occurrence.