Photodynamic therapy is brand new knowledge, whether for clinical or teaching and research. Photodynamic therapy was first used for the diagnosis and treatment of tumors and clinically for the treatment of acromegaly I. What is photodynamic therapy (PDT)? a) Photodynamic therapy is a new means of disease treatment based on the interaction of light, photosensitizers and oxygen. b) The basis of the action of photodynamic therapy: photodynamic effect It is a kind of photosensitization reaction accompanied by biological effect with the participation of oxygen molecules. The process is: the light irradiation of specific wavelength causes the tissue absorbing photosensitizer to be excited, and the excited state of the photosensitizer in turn transfers energy to the surrounding oxygen, generating highly reactive monomorphic oxygen, which reacts with adjacent biological macromolecules to produce cytotoxic effects, thus leading to cell damage or even death. The three elements of the photodynamic effect are: photosensitizers: their photodynamic activity, light absorption properties and targeting properties determine their clinical availability and scope of application. Irradiated light: its correct wavelength, output stability and cast reliability are also important controllable factors determining the therapeutic effect. Oxygen: In the excited state, the photosensitizer transmits energy to oxygen in the surrounding tissue, which generates highly reactive monomorphic oxygen and stimulates the production of a large number of free radicals, which in turn mediates cytotoxic effects. Since photodynamics is performed on living bodies and living tissues are oxygenated, no additional oxygen needs to be introduced to initiate photodynamic therapy. c) Why can photodynamic effects be used to treat diseases? There are two prerequisites for the photodynamic effect to be used for disease treatment: 1) the specific diseased tissue is able to take up and retain more of the photosensitizer, and 2) the target site is more susceptible to light irradiation. Only if the above two prerequisites can be achieved, the strong photodynamic effect can occur and the diseased tissue can be adequately destroyed. In addition, in photodynamic therapy, in addition to the monomorphic oxygen and free radicals generated during the conversion of light energy that can directly kill lesion cells, local microcirculatory disorders caused by capillary endothelial lesions and vascular embolism triggered by this process further lead to ischemic necrosis of lesion tissues. Clinical indications of ALA-PDT (dermatological application) 1. In November 1999, the US FDA officially approved ALA-PDT for the treatment of actinic keratosis 2. In June 2001, Sweden also approved methyl aminoketovalerate photodynamic therapy for the treatment of actinic keratosis and basal cell carcinoma of the head and face that are not suitable for traditional therapy 3. PDT clinical application Some basal cell carcinoma, squamous cell carcinoma, actinic keratosis, Bowen’s disease, Bowen-like papulosis, etc. have been studied clinically and scientifically, and more satisfactory treatment effects and reliable scientific data have been obtained. Because of good safety, non-invasive and better protection of normal tissue structure, it is especially suitable for the treatment of skin tumors in facial and genital areas and patients who are limited by traditional laser and surgical treatment. It is worthy of clinical promotion and application. Hundreds of patients with urethral condyloma acuminata treated by this therapy have achieved very satisfactory results, proving that ALA-PDT is a new treatment for urethral condyloma acuminata that is simple, highly effective, with low recurrence rate, no significant pain and no complications.