Cystic acne is similar to nodular acne, but larger. The inflammation of this type of acne penetrates deep into the bottom layer of the skin and is filled with pus, which is also more painful. It takes a long time to heal, and it also has the highest chance of leaving a scar. Cystic acne is usually caused by the dead skin cells deep in the pores blocking the pores and the imbalance of oil and water in the sebum. This situation will aggravate the proliferation of acne bacteria, then the acne will become inflamed and swollen, forming cystic acne.