PhotodynamicTherapy (PDT), also known as light irradiation therapy or photochemotherapy, is a new technology that uses photodynamic reactions for disease diagnosis and treatment based on the interaction of light, photosensitizers and oxygen. The mechanism of acne treatment 1. Photodynamic therapy directly kills Propionibacterium acnes; 2. Targeted action on sebaceous glands, reversible damage to sebaceous glands, and inhibition of sebum production; 3. Action on keratin-forming cells to reduce follicle blockage; 4. Red light – anti-inflammatory and restorative effects. Photodynamic therapy (PDT) is a safe and effective non-invasive treatment method developed in recent years. ALA is expected to be the main drug in photodynamic treatment of acne! u5% ALA-PDT for acne has an efficiency of 70%-80%, comparable to existing mainstream methods, but with mild adverse effects, only local therapeutic reactions occur, no systemic toxic side effects, no special treatment is needed, and it can be relieved by itself. The efficacy of ALA-PDT for acne treatment is positively correlated with the number of treatments, and increasing the number of treatments can significantly improve the efficacy.