Cystic acne is a type of inflammatory acne that causes painful, pus-filled pimples to form deep under the skin. It is the most severe form of acne and can cause long-lasting damage, both psychologically and physically. Cystic acne occurs when oil and dead skin cells build up deep within hair follicles, causing a rupture within the skin. Bacteria can also get trapped in the pores, causing the area to become red and swollen. Cystic acne is different from other types of acne because it is filled with pus, a fluid that acne nodules do not contain. Hormones called androgens play a role in the development of cystic acne, and other factors that can cause acne include a womans menstrual cycle, pregnancy, and menopause. A dermatologist can help with a treatment plan for cystic acne, which can last for years and affect large areas of the skin, leaving scars.