Photodynamic therapy is a promising, minimally invasive, and clinically approved treatment strategy that destroys the cell components by oxidizing the biological molecules such as nucleic acids, carbohydrates, proteins, and lipids, and leads apoptosis in the cells of the target tissue through the generation of singlet oxygen and reactive oxygen species (ROS) owing to the synergic interactions of a nontoxic photosensitizer, a non-thermal light source, and tissue oxygen. This innovative method has drawn the attention of many scientists and been employed in a wide range of medical fields that covers the treatment of cancer diseases and precancerous dermatological disorders, and the aesthetic and cosmetic practices, including photorejuvenation and treatment of photoaging, hirsutism, facial flat warts, rosacea, acne vulgaris, and sebaceous gland hyperplasia. It was therefore intended to provide an in vitro photodynamic therapy assay protocol on human healthy keratinocytes and epidermoid carcinomas to investigate comparatively the therapeutic and destructive activities of the potent light-sensitive medications.