Protection afforded by sunscreens containing inorganic sunscreening agents against blue light sensitivity induced by aminolevulinic acid.

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/cm(2) for skin protected with sunscreen containing iron oxide 3.2% and 0.2%, respectively, and 10.6 J/cm(2) 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.