# Photodynamic Therapy--An Up-to-Date Review
## 5 Photodynamic Therapy Applications
### Non-Malignant Diseases  
Despite being best-known for cancer treatment, PDT is not limited to destroying tumoral cells. At the beginning of the last century, the photodynamic effect was demonstrated against bacteria. Considering the present challenges of antibiotic resistance and the rise of new infections, it is no surprise that PDT gained attention for fighting against bacteria, fungi, viruses, and protozoa [17; 35].  
Antimicrobial photodynamic therapy (found in the literature also as \"photodynamic inactivation\") is a safe and cost-effective method to treat various infectious diseases [33]. This is of great importance since the skin and soft tissue lesions can easily become infected by multi-drug resistant pathogens that delay proper healing. Moreover, classic local therapies for infected wounds from burns, trauma, surgery, or diseases are expensive and frequently ineffective [140; 141]. As a solution, PDT has been proposed for the treatment of localized bacterial infections. PDT has shown excellent wound healing results, accelerating tissue repair by killing bacterial cells and simultaneously stimulating fibroblasts' proliferation [142].  
Dental infections represent one of the greatest expanding fields of clinical antibacterial PDT. Studies have reported that pathogens prevalent in the subgingival periodontal plaques (e.g., _Perplyromonas gingivalis_, _Fusobacterium nucleatum_, _Staphylococcus_ spp.) have been successfully destroyed through photodynamic treatment, both in aqueous suspension and as a biofilm [33; 143].  
Another application of PDT is for treating fungal infections. These infections are increasing in prevalence worldwide, especially because only three major classes of antifungal drugs are available for invasive infections, and the efficiency of the treatment depends on the patient's immune response [19]. A particular case is represented by onychomycosis, one of the most frequent and severe nail fungal infections [144]. PDT is considered promising towards treating this disease through an appropriate formulation, including a PS and keratolytic agents that would increase nail plates' permeability towards active agents uptake [17].  
PDT has been reported to be effective in the inactivation of mammalian viruses, such as human immunodeficiency virus (HIV), human papillomavirus (HPV), hepatitis A, B, and C viruses, herpes viruses, human parvovirus B19, human cytomegalovirusovirus, enteroviruses, and adenovirus [145; 146; 147]. PDT started to be intensively researched in the pandemic context as an alternative or complementary treatment strategy to target SARS-CoV-2 [34; 148; 149; 150; 151; 152]. The photodynamic effect can disrupt the membrane structures of the viral envelope, proteins, and RNA. Hence, PDT is proving to be a powerful tool to inactivate infectious agents [34; 152].  
Besides pathogen-related diseases, PDT can be employed in the treatment of central serous chorioretinopathy (CSC). This condition is caused by the serous retinal detachment and retinal pigment epithelial detachment at the macula, leading to visual difficulties under low light levels [153]. Several treatments have been proposed to treat CSC (e.g., laser photo-coagulation, carbonic anhydrase inhibitors), yet they are not specific enough in dealing with this fundamental choroidal vascular issue [154]. Fortunately, PDT seems effective for treating CSC, as it impacts choroidal vasculature structure, altering its permeability [154; 155; 156].