Reddening pimples are medically known as inflammatory papules. Inflammatory papules are also one of the manifestations of acne. Inflammatory papules are mainly associated with infection by Propionibacterium acnes. The secretion and discharge of large amounts of sebum is impaired, and it is easy to develop bacterial infections. There are many microorganisms in the sebaceous follicles, such as Propionibacterium acnes, Staphylococcus albicans and Malassezia furfur. Among them, Propionibacterium acnes is the most important. This bacterium is anaerobic, and the obstruction of sebum discharge creates a good local anaerobic environment for it, which allows Propionibacterium acnes to multiply. The lipase produced by Propionibacterium acnes breaks down triacylglycerols in sebum to produce free fatty acids, which are irritating to the skin and hair follicles. In addition, P. acnes also produces peptides that chemotacticize neutrophils, activate complement and cause leukocytes to release various enzymes, causing an inflammatory response, which results in the formation of red acne.