Acne (pimples) is a chronic inflammatory skin disease of the sebaceous glands. Its prevalence is 70% to 87%, and severe cases can leave acne scars (pits) that seriously affect appearance. The psychological and social impact of acne on adolescents exceeds that of asthma and epilepsy. The occurrence of acne is closely related to many factors such as excessive sebum production, blockage of sebaceous ducts in hair follicles, bacterial infection and inflammatory response. The pathophysiological basis of acne has three major aspects: 1) rapid development of sebaceous glands and excessive secretion of sebum; 2) abnormal keratinization of follicular sebaceous ducts; 3) secretion and drainage of large amounts of sebum secondary to bacterial infection and inflammatory reaction. These three aspects are influenced by a variety of factors such as neurological, psychological, endocrine, metabolic, and immune infections, so their prevention and treatment are somewhat uncontrollable. There are various methods of treating acne (sebaceous glands and Acinetobacter are the main targets of treatment): topical cleansing, topical medications, antibiotics, retinoic acid, hormones, herbal medicine and physical therapy. Each treatment can work on one or more aspects of the condition. For acne patients who cannot tolerate medication or do not want to be treated with medication, physical therapy is the best option. Physical therapy includes photodynamic therapy, laser therapy, and fruit acid therapy. Among them, photodynamic therapy has unique advantages in targeting sebaceous glands and Acinetobacter: Photodynamic (PDT) is the use of light to activate intracellular or extracellular sources or endogenously formed photosensitizers, forming monomorphic oxygen or other free forms of free radicals to treat acne through phototoxic reactions, induction of cell death, and stimulation of macrophages to release cytokines and promote self-healing of lesions. At present, the photosensitizing substances used on PDT are mainly ALA, MAL and ICG, among which ALA is the most commonly used. The domestic ones used for acne treatment are YiYan, which has strong lipophilicity. After applying it to acne skin for one hour, there is a higher concentration of the active ingredient of ALA in the sebaceous glands, and it is converted into an endogenous photosensitizer through the heme synthesis pathway, and then produced when irradiated with specific wavelengths of light The latter selectively kills Propionibacterium acnes and destroys part of the sebaceous glands, and generally acne can be better controlled through three treatments. Precautions related to photodynamic acne treatment: Some patients will experience acne breakouts after the first treatment, which is a normal phenomenon due to the inflammatory response after treatment triggering the underlying acne, which instead signals a better efficacy; cold compresses of the mask can be applied after treatment to reduce the reaction; the skin will have mild swelling after treatment, which lasts 1-2 days and usually fades in 72 hours; due to the destruction of sebaceous glands The skin will be dry and flaky in the short term, so pay attention to local cleaning and moisturizing; pay attention to sun protection after treatment to avoid leaving pigmentation; photodynamic power is not a panacea and cannot absolutely control acne in all patients; the effect of photodynamic therapy cannot be permanent, so you need to make adjustments to your life, physiology and psychology to maintain a good state.