One of the causes of acne is the action of Propionibacterium acnes. This cause accounts for a large percentage of patients with either mild or severe acne, and red and blue light treatment is aimed at solving the problem by addressing this causative agent. Wu Minzhi, Department of Dermatology and Venereology, Suzhou Fifth People’s Hospital The treatment principle of red and blue light: Propionibacterium acnes can synthesize and store a metabolite called porphyrin. Blue light is superficial, with a heavy phototoxic reaction, and works better on inflammatory papules and pustules; red light penetrates deeper, with a slightly lighter phototoxic reaction, but can inhibit sebaceous gland secretion and promote tissue repair. Therefore, alternating red and blue light can clear acne lesions faster, promote repair, and inhibit sebaceous gland secretion, making acne less likely to recur. In addition to red and blue light treatment, acne squeezing, topical medication or oral medication can be combined. The treatment method is chosen according to the type and classification of acne and the patient’s own situation.