Photodynamic therapy (PDT) is a form of phototherapy involving light and special drugs called as photosensitizing chemical substance get activated(become toxic) in certain kinds of lights. It is used in conjunction with molecular oxygen to elicit cell death through phototoxicity. The therapy has proven ability to kill microbial cells, including bacteria, fungi and viruses. Photodynamic therapy (PDT) is popularly used in treating acne. It is used clinically to treat a wide range of medical conditions, including wet age-related macular degeneration, psoriasis, and atherosclerosis and has shown some efficacy in anti-viral treatments, including herpes. It is also used to treat malignant cancers including head and neck, lung, bladder and particular skin. The therapy has also been tested for treatment of prostate cancer, both in a dog model and in human prostate cancer patients.