There are two different classifications, non-inflammatory, which as you might imagine is less severe and inflammatory acne. Within these two classifications are several different types.
Then you’ve got your inflammatory acne, which can be significantly more problematic. The problem lies with bacteria, the result generally an inflammation that swells, or becomes red and inflamed. Within the inflammatory acne category, there are three primary types, with increasing degrees of severity: papules (relatively mild, and with no pus), pustules (more severe, inflamed, pus often apparent) and cysts or nodules (big, painful to the touch, generally red and inflamed with pus).