Inflammatory acne encompasses papules, pustules, and nodulocystic lesions.  Papules are inflamed with a raised, reddened are on the skin.  Nodules are papules with more extensive penetration into surrounding tissue.  Pustules are essentially papules that contain pus.  Pustular acne is more likely to result in permanent scarring.

It is believed that when the follicular wall ruptures this sets off a process by which the inflammatory process occurs.  Sebum, which contains triglycerides is acted upon by bacterial organisms (generally Propionibacterium acnes) causing the formation of fatty acids.  The fatty acids are believed to be the cause of the inflammation.  Topical antibiotics suppress the bacteria that are responsible for the fatty acid formation thus reducing the inflammatory process.