Photodynamic therapy requires three basic elements to work:

1. A photosensitizer:
   Acne light treatment is based on the fact that P. acnes bacteria produce porphyrinsas metabolic products. These porphyrins act as internal photosensitisers inside the pilosebaceousfollicle and are activated by visible light, creating a photochemical reaction which eradicates bacteria. The external application of a photosensitizing substance leads to an increase in the porphyrin concetration, which when exposed to visible light produce free radicals thatdestroy P. acnes bacteria.
2. Light source:The wave length which is chosen for the light source depends on the depth of the penetration. Porphyrin absorption lies within the visible spectrum  in a wave length of 300-650nm. It is proven that blue light is more effective in activating porphyrins than the red, but red light penetrates deeper. A special device emitting this wave lengths is used as the source of blue and red light.
3. Oxygen (O2):Porphyrin is activated by the application of  visible light and reacts with oxygen resultingin the production of active free radicals, which cause damage to the membranesand therefore cellular death. Thereby bactericidal activity is achieved.