Acne occurs when the pores of the skin become clogged, most often on the face. Once a pore becomes clogged, it traps skin oil inside. Bacteria grows in this oil and can cause an inflammatory response in the skin. Acnelesions can be small and hardly noticeable, appear as a small whitehead or blackhead, or can appear red with a white/yellow center. Sometimes a clogged pore will become so inflamed that it can lead to larger, more painful lesions (nodules or cysts), which can ultimately scar.