What are the causes of nodular acne?

Nodular acne develops when the hair follicles in the skin become plugged with dead skin cells, oil and bacteria, explains Mayo Clinic. Hard, painful bumps develop deep below the skin's surface, according to WebMD. Acne nodules may need to be treated by a dermatologist to achieve clear skin.

Three things contribute to the development of nodular and other forms of acne: overproduction of sebum, or oil, irritation to the hair follicles caused by improper shedding of dead skin cells, and build up of bacteria within the pores. Hormone fluctuations, poor diet and certain medications may contribute to the development of nodular acne, according to Mayo Clinic.