Because it can vary greatly from person to person, defining exactly what causes cystic acne in any one person can be rather complicated, but the general causes of cystic acne are well understood. At a rudimentary level, cystic acne, which is characterized by a painful infected cyst as the base of a hair follicle, has the same cause as regular acne, a blocked pore on the surface of the skin.

What Causes a Blocked Pore?

Pores are openings on the surface of the skin through which hair grows. The pathway from the root of the hair to the pore is a follicle. At the base of each follicle is a sebaceous gland that produced an oil known as sebum, which is used by the body to lubricate the skin and help remove dead skin cells. A pore can become blocked when the sebaceous gland over-produces sebum, causing the follicle to become plugged with oil, dead skin cells, and bacteria. When the blockage causes an infection at the base of the follicle, cystic acne can result. Alternatively, oily skin or hair products can also block pores, but this usually leads to whiteheads or blackheads rather than cystic acne.

What Causes Excess Oil Production?

Hormonal shifts are the main cause of excess sebum production by the sebaceous gland. This is why acne is most common during the momentous hormone changes that occur during puberty. Acne causing hormone shifts can also occur during the menstrual cycle, during pregnancy, at menopause, during periods of great stress, and when beginning, changing, or stopping the use of a hormonal contraceptive. Drugs that contain hormones such as testosterone or female hormone replacement therapies can also trigger excess sebum production, as can drugs that impact hormone production, such as steroids. Despite popular belief, there is no indication that certain foods such as french fries, pizza, or chocolate cause excess sebum production or contribute to acne in any other way. 

Don't Exacerbate It

There are several things that can make cystic acne worse. The cysts themselves can be painful and itchy, but trying to scratch or pop them could spread the infection to other follicles as well as increasing the chance of scarring. Even applying skin makeups such as foundations or powders can cause the acne to spread.