What is photodynamic therapy? Photodynamic therapy (PDT) is a new selective treatment technique introduced in the late 1970s and rapidly developed in recent years, which is completely different from surgery, radiotherapy, chemotherapy and immunotherapy. Its action is based on systemic or topical application of photosensitizers after the application of specific wavelengths of light irradiation in a specific period of time, the photosensitizers produce a series of photochemical and photobiological reactions, causing tissue damage, so as to achieve the purpose of treating the disease. The commonly used photosensitizer for the skin is 5-aminoketovaleric acid [ALA], which is applied to the mucosal surface of the skin and irradiated with a laser at a wavelength of 630-635 nm. What are the advantages of photodynamic therapy? The advantages of photodynamic therapy are: Wide range of indications: various types of target cells, effective for a variety of tumors, viral infections and vascular lesions. Easy to use, easy to operate: no need to inject or take any drugs orally, just seal the agent on the skin, wait for its complete absorption, and then supplement with laser irradiation for 20 minutes. Low toxicity, high selectivity: it is a local treatment method, the target of attack is the diseased tissue in the light irradiated area, the part not irradiated by light, and does not produce this reaction, other parts of the organs and tissues are not damaged, except for a mild burning sensation in the irradiated area, there are almost no toxic side effects. For the function and appearance of the face, genitalia and other special parts can also play a good role in protecting. Elimination of latent lesions: This is an advantage unique to photodynamic therapy. Some diseases that may have latent lesions, such as extramammary Paget’s disease and condyloma acuminata, conventional means can only remove the main lesion and can do nothing for latent lesions or subclinical infections, but surface irradiation with photodynamic therapy can destroy all the tiny lesions that may exist, greatly reducing the chance of disease recurrence. Repeatable: Target cells are not resistant to photosensitizing drugs, and patients do not experience increased toxicity from multiple photodynamic treatments, so treatment can be repeated. Palliative treatment is possible: For certain patients who are too old, have cardiopulmonary, hepatic and renal insufficiency, or hemophilia and cannot receive surgical treatment, photodynamic therapy is a palliative treatment method that can effectively reduce pain, improve quality of life, and prolong life. Indications for photodynamic therapy? China is one of the earliest countries in the world to carry out photodynamic therapy, and it is also the country with the largest number of treatment cases in the world. The “tumor photodynamic diagnosis and treatment” has been listed as the key scientific and technological projects of the 6th and 7th Five-Year Plan. My dermatology department also introduced this equipment for the diagnosis and treatment of skin diseases, mainly for: human papilloma virus infected skin disease [condyloma acuminata]: for latent infection lesions have specific efficacy, painful effect, low recurrence rate, especially for the urethra, cervix and other difficult to treat condyloma acuminata treatment. Bowen’s disease, basal cell carcinoma, mycosis fungoides, squamous cell carcinoma and solar keratosis, Queyrat proliferative erythema (EQ) and other skin malignancies and precancerous lesions: its advantages are non-invasive, less painful, can be a useful supplement to surgery, and has special application for older and frail patients and more special areas such as genitalia. Vascular malformations: especially erythema-like nevi, the advantages of which are ideal treatment effect, no scar residue, and mild pain, which have positive significance for the treatment of young patients and facial areas. Other diseases such as acne, scleroderma, Bowen-like papulosis and psoriasis: ALA-photodynamic therapy also has very good therapeutic effects. Throughout the development process and the characteristics of photodynamic therapy, it will become another tool in dermatology treatment due to its special advantages, which will bring benefits to more patients.