Cystic acne, also known as nodulocystic acne, is different from normal acne. It is not only the most painful form of acne, but also very severe in its exhibited symptoms. It is basically an acne that has developed into a cyst. A cyst is a closed sac with a membrane and some tissues, that get painfully inflamed. If left untreated, it can recur and may leave a scar behind.