Acne is a chronic inflammatory disease associated with multiple factors and is somewhat cosmetic in nature. Its development is mainly related to androgen levels, increased sebaceous secretion, hyperkeratosis at the opening of the sebaceous glands of the hair follicles, and Propionibacterium acnes infection. Clinical Classification] Acne can be classified as mild, moderate or severe according to the severity of the disease. Mild acne is characterized by disseminated to multiple blackheads, which may be accompanied by scattered inflammatory papules; moderate acne is characterized by acne and an increased number of inflammatory papules and pustules; severe acne is characterized by nodules, cysts and scar formation, which seriously affects the patient’s image. Graded treatment】 The principles of treatment are mainly lipid removal, dissolution of keratin, sterilization, anti-inflammation and regulation of hormone levels. Mild acne is generally treated locally with drugs and medical skin care products that exfoliate, dissolve acne, inhibit sebum secretion and are antibacterial. Moderate acne can be treated with Chinese herbal medicine such as herbal decoction or Chinese herbal medicine such as Danshinone and Dotted Tongue Pill, which can be used internally in combination with topical medication. For severe acne, oral isotretinoin soft capsules are effective, but maintenance treatment should be up to 4-6 months or more. Our department applies photodynamic therapy for severe acne and has achieved good results. We believe that photodynamic therapy is the ideal treatment for severe acne, which is fast, efficient and can improve skin quality, shrink pores and tighten the skin as a whole while treating acne. Photodynamic Therapy Photodynamic therapy is a photochemical reaction caused by the excitation of a photosensitizer by light energy, which can be used to selectively destroy biological tissue. The principle of action of photodynamic therapy is based on the photodynamic effect, which is a photosensitization reaction with biological effects involving oxygen molecules. The process is as follows: light irradiation of specific wavelengths excites the photosensitizer absorbed by the tissue, and the excited photosensitizer in turn transfers energy to the surrounding oxygen, generating highly active monomorphic oxygen, which reacts with adjacent biological macromolecules to produce cytotoxic effects, leading to cell damage, death, and finally shedding, thus achieving the purpose of treatment. Advantages 1. Directly targeting the pathophysiological process of acne, with simultaneous action of multiple pathways, remarkable efficacy and long-lasting effect; 2. Local topical treatment, no systemic toxic side effects, no drug resistance generation, repeatable treatment; 3. Long-term inhibition of sebum secretion, lasting resistance to acne recurrence; 4. Anti-inflammatory repair and prevention of scar formation.