Skin should be protected from sunlight, even through window glass or on a cloudy day, for at least 24 hours before and 8 hours following oral PUVA treatment by protective clothing, such as long-sleeved shirts, full-length slacks, wide-brimmed hat, and gloves and by using a sun block product that has a skin protection factor of at least 15 on body areas that cannot be covered by clothing. In addition, lips should be protected with a sun block lipstick that has a skin protection factor of at least 15. Also, since the skin continues to be sensitive to sunlight for some time after treatment, the patient should avoid overexposure to sunlight for 48 hours following administration of trioxsalen. . Trisoralen Drug Information from Drugs.com. Includes Trisoralen side effects, interactions and indications..