Photodynamic therapy is an emerging method for local destruction of tissue by generating toxic oxygen species using light absorbed by an administered or an endogenously generated photosensitiser. It is a promising treatment for patients with cancer. More recently it has found increasing use as a method of therapy for non-cancerous illnesses. Following administration of a photosensitiser occurs an accumulation or retention in areas of cancer and disease relative to adjacent normal tissue. The photosensitiser is inactive until irradiated by light, following which cellular destruction occurs. This explanation is a good reason for the scientific and clinical interest in photodynamic therapy.