Acne, commonly known as “pimples,” occurs mainly on the face, forehead and back. Severe acne, with extensive lesions, is difficult to treat. The long-lasting lesions and scarring affect the patient’s appearance and psychological well-being. Photodynamic therapy now offers a new treatment option for patients with severe acne, with remarkable efficacy. Treatment principle: With the help of specific drugs (photosensitizers) entering the patient’s skin, concentrated in the hair follicles and sebaceous glands. Under certain wavelengths of light irradiation, the photosensitizer will produce active oxygen and other substances that can directly kill Propionibacterium acnes; act directly on the sebaceous glands to permanently reduce sebum secretion; improve the blood and lymphatic microcirculation of the skin, regulate immune cell activity, and reduce inflammation; and promote dermal collagen repair to reduce scar formation.