After applying the photosensitizing liquid, there is an incubation period of around an hour to two hours, after which the target tissue is then selectively exposed to a specific wavelength of light that then activates the photosensitizing medication. The optimal light depends on the ideal wavelength for the particular drug used and how far the light can travel in the target tissue. Thus, specific photosensitizers and wavelengths of light are used to treat different areas of the body with PDT.

When photosensitizers are exposed to the appropriate wavelength of blue light, they enter an excited state to stimulate porphyrin, the metabolite of proprionbacteria in acne, to produce the formation of a reactive state of oxygen known as singlet oxygen, which is highly toxic to bacteria in nearby cells that have both selectively taken up the photosensitizer and have been locally exposed to light. Because not all tissues of an entire area of treatment may have met both criteria for targeted treatment, subsequent treatments may be necessary to remove acne.

Red light, because of its longer wavelength, penetrates deeper into the skin than blue light and is more effective for the treatment of thicker actinic keratosis lesions and deeper targets such as the sebaceous gland, following the production of singlet oxygen, which is highly toxic to actinic keratosis and superficial basal cell carcinomas because they selectively uptake a significant amount of the photosensitizing agent, more so than in normal cells. Tiny actinic keratosis spots are also treated to prevent them from growing cancerous. With traditional cryosurgery, only the visible actinic keratoses can be treated. Since many actinic keratoses are often not detected with the naked eye, PDT is preferable to cyrosurgery since it is expected to destroy the seemingly invisible actinic keratosis lesions. Thus, the entire area of the skin on your face is treated with PDT. Red light is also effective in promoting growth of fiber cells, stimulating collagen production, thickening and restructuring the dermis structure, and for increasing the elasticity of the skin, for smoother skin. Skin redness and irritation are common side effects following PDT, which is controlled to a significant extent by applying a calming mask post procedure. Once the areas have healed following PDT, the areas are reexamined to see if additional treatments or biopsies are needed.

PDT is a three-step treatment. First, a light-sensitizing liquid, is applied to the area. Second, there is an incubation period of about an hour. Finally, the target tissue is then exposed to a specific wavelength of light that then activates the photosensitizing medication.