The causes of acne are complex and are mainly related to androgens, increased sebum secretion, abnormal keratinization of hair follicle sebaceous ducts, proliferation of Propionibacterium acnes and genetics. The sebaceous glands are mainly regulated by androgens. After puberty, androgens increase the size of the sebaceous glands and increase sebum secretion activities. Sebum provides the material basis for the growth of normal parasitic bacteria such as Propionibacterium acnes, Malassezia ovalis, and Staphylococcus epidermidis in the hair follicles. Propionibacterium acnes can hydrolyze triglycerides in sebum to produce free fatty acids and some low-molecular polypeptides. Free fatty acids can stimulate the hair follicle wall and cause inflammation, while stimulating the epithelial hyperplasia and hyperfocalization of the hair follicle sebaceous gland ducts, resulting in blocked sebum secretion, poor excretion, and acne. Free fatty acids and these low molecular peptides can chemotactic neutrophils and other inflammatory cells, the latter producing hydrolytic enzymes that can damage or even rupture the follicle wall and spill the follicle contents into the dermis to further aggravate the inflammatory response, resulting in a series of lesions ranging from inflammatory papules to cysts. In some patients, the occurrence of acne is also related to genetics, immunity, use of cosmetics, dietary stimulation and endocrine disorders, which are manifested in familial clusters of acne, fulminant acne or acne flares associated with the menstrual cycle.