Effect of dark test-substance pigmentation on skin perfusion assessments and effect of test technique on balsam of Peru patch-test results

13 balsam of Peru (Myroxylon Pereirae) patch-test-positive subjects are re-tested with 25% balsam of Peru in petrolatum and with serial doses printed on polyester squares. All substances are applied with tape strips for 3, 6, 24 (1 day [D]), 48 (2D), 72 (3D) and 96 h (4D) on each subject and for 96 h (4D) with plastic foils. Tests are followed visually and with perfusion assessments from 3 h to 9 days. Results show that pigment remnants following detachment of patches affect perfusion assessments. Such effect due to pigment is supported by readings of patch tests through the petrolatum test substance while applied with transparent foils. For most reactions, good agreement is observed between the assessment techniques when peak assessment values of reactions are compared. There is inter-individual variation in perfusion with identical tests. With the petrolatum test substance, increased visible reactivity was observed when the application time was extended up to 24 h (1D), while extension of application time increased perfusion in most cases except for an extension from 24 (2D) to 48 h (4D) where decreased perfusion resulted in most cases. Dose and application time did not affect the timing of highest reactivity of reactions in most cases.