BACKGROUND Application of aminolevulinic acid (ALA) for photodynamic therapy induces significant sensitivity to visible light. OBJECTIVE To determine whether sunscreens containing inorganic agents are effective against sensitivity to blue light induced by ALA application. METHODS & MATERIALS Twenty subjects received application of ALA on the arm. Thirty minutes before blue light exposure, two sun protection factor 50 inorganic-based sunscreens containing iron oxide 3.2% and 0.2% were applied on separate areas where ALA was applied; a third area received no sunscreen. Small areas of skin were exposed to increasing fluences of blue light 3 or 18 hours later, and the minimal phototoxic dose (MPD) was noted. RESULTS Three hours after ALA application MPD was 29.2 and 22.6 J/cm2 for skin protected with sunscreen containing iron oxide 3.2% and 0.2%, respectively, and 10.6 J/cm2 for unprotected skin (p=.003 and .0497 respectively). At 18 hours after ALA application, MPD for sunscreen containing iron oxide 3.2% was 5.78, compared with 0.33 for unprotected skin (p<.001) with a blue light protection factor of 21. CONCLUSION The sunscreen containing iron oxide 3.2% afforded significant protection against blue light sensitivity induced by ALA application. The authors received a research grant from Laboratoires Dermatologiques Avène to conduct the study. Sophie Méry and Thérèse Nocera are employees of Pierre Fabre Dermo-Cosmétique, and Sophie Méry was in charge of the statistical analysis subcontracting.