PDT has been FDA approved for the treatment of precancerous lesions (actinic keratoses). The original FDA approval involved the overnight application of the Levulan medication, with light treatment the following day. Side effects and discomfort were much more unpleasant with this method. For this reason, PDT is more commonly being performed with a 1-3 hour application time of Levulan. PDT is also being used to treat acne because of its shrinking effects on sebaceous glands.