There are several different types of acne, but the most common types include blackheads, whiteheads, pimples, papules, nodules, and cysts. Comedonal acne, such as blackheads and whiteheads, develops when your pores become clogged with oil and dead skin cells. If the pore is open, the contents will oxidize, leading to a closed comedone (or a blackhead). If the pore is closed, a whitehead will develop.
When bacteria enter the clogged pore, more stubborn forms of acne—those pesky pimples, pustules, and nodules—can occur. Finally, there’s cystic acne, which is generally considered the most difficult to treat. This type of acne causes pus-filled cysts to develop deep in your skin and generally requires a dermatologist to treat effectively.