Acne is a common chronic inflammatory disease involving the sebaceous glands of the hair follicles, and is somewhat disfiguring. It can affect people of all ages, with a higher incidence in young people. The development of acne is mainly related to four major causes: sebaceous gland hyperfunction, follicular sebaceous gland duct keratinization blockage, Propionibacterium acnes infection and inflammation. Concerns about the adverse effects of drug therapy (hepatotoxicity and teratogenicity) have limited the use of these traditional treatments. For patients who cannot tolerate or do not wish to receive medication, physical therapy is the best option, with red and blue light becoming the basic treatment for acne. Red and blue light are visible light, non-radiation, safe and effective. Currently, simple blue light, simple red light, blue light and red light combined therapy, and red light combined with 5-ALA photodynamic therapy are mainly used in clinical treatment of acne. 1. Blue light therapy: mainly used for the treatment of mild to moderate acne. Propionibacterium acnes produces protoporphyrin IX and fecal porphyrin during its own metabolism, and the porphyrin absorbs blue light to produce singlet oxygen and free radicals, which rapidly kills Propionibacterium acnes and inhibits sebaceous cells from secreting sebum and reduces inflammatory reactions. However, the depth of penetration of blue light is limited, so it is necessary to have several consecutive treatments, and therefore blue light is suitable for: greasy skin, superficial inflammatory papules, pustules, and the effect on the deeper cysts and nodules is not good. In order to enhance the therapeutic effect, combined treatment can also be used, such as traditional Chinese medicine inversion mold combined with blue light treatment for moderate acne. 2. Red light therapy: It is mainly used for deeper acne inflammatory papules and as a basic treatment for post-acne skin repair. Red light penetrates deeper than blue light, can enter the dermis, in anti-inflammatory treatment at the same time, stimulate macrophages to release a variety of cytokines to promote the proliferation of fibroblasts in order to achieve the role of skin repair, the treatment can significantly improve the skin texture and hyperpigmentation, the histological manifestation of the reduction of pigmentation particles in the basal layer (whitening), dermal collagen fibers aligned neatly and tightly (rejuvenation), collagen fibers fractured, disorganized and aggregated into a certain phenomenon. disorders and aggregation of collagen fibers are somewhat improved (can treat photoaging). Although the skin pigmentation and texture improvement on the red light photodynamic significantly better than simple red light therapy, but red light therapy painless, inexpensive, simple and easy to adapt to a wider range of people. 3, the combined treatment of blue light and red light: can have antibacterial, anti-inflammatory and repair effects at the same time. It has a good effect on mild to moderate acne. Some scholars have shown that after patients receive treatment twice a week for 4 weeks, the acne and inflammatory lesions of the patients were significantly reduced, and the efficacy of the treatment was better than that of using blue light alone. 20 minutes each time, 2 to 3 times a week, 8-10 times for a course of treatment. 4, red light combined with ALA photodynamic therapy: mainly used to treat moderate to severe and cystic acne. Red light combined with ALA photodynamic therapy can be used to treat deeper acne cysts and nodules (which are difficult to treat with medication), and at the same time, the skin repair effect is obvious. It is a fast, effective and safe treatment for moderate to severe acne that minimizes scarring and is the preferred physical therapy for severe acne. Red and blue light provides a safe and effective treatment option for a wide range of acne patients, and can be used alone or in conjunction with medication and/or other physical therapy. Early treatment of acne can help shorten the course of treatment, reduce recurrence, and prevent scar formation.