Levulan is a topical photosensitizing agent which is absorbed by abnormal cells, pores, and oil glands.
When you combine Levulan with Blu-U light treatment you get the most effective acne treatment because Levulan makes the skin area more susceptible to the blue light treatment.
Note that if you are taking Accutane, or have Lupus or other light sensitive conditions, or are pregnant or breast feeding you cannot have Blu-U Levulan.