INS and infection: Key factors in the development of acne are an increased or altered sebum production by piliferous glands (hyperseborrhea and dysseborrhea), changes in keratinization, skin inflammation, and infection of piliferous glands by Propionibacterium acnes; moreover, changes in hormone secretion, particularly androgens, insulin, and insulin-like growth factor-1, play a centrale role too [61,62].