Dressler, W.E., R. S. Grabarz, and R. K. Sharma. Comparison of Percutaneous Absorption Characteristics for Two Structurally Related Direct Hair Dyes, HC Blue No. 1 and HC Blue No. 2, In Vitro and In Vivo. The Toxicologist 1999. 48(1S): 74. Abstract #345.

Two structurally related direct (semi-permanent) hair dyes, HC Blue No. 1 and HC Blue No. 2, were compared for their percutaneous absorption potential using human cadaver skin mounted in Franz-type static diffusion cells in vitro. Under simulated use conditions, [14C]-radiolabeled dyes in hair dye formulations for which human in vivo penetration data had been obtained preivously (Wolfram, L.J., Maibach, H.I. 1985. Arch. Dermatol. Res. 277: 235-241) were applied to heat-separated epidermal membranes. The appearance of [14C] in 30 minute skin rinsates, in periodic receptor fluid samples, and in both a final wash and the epidermis after termination of the experiment at 48 hours was determined via liquid scintillation. For HC Blue No. 2, the absorption of dye into the receptor fluid was maximal within 4 hours after application, with a total cumulative mass absorbed of about 0.20 ug/cm2. For HC Blue No. 1 the cumulative mass absorbed was 0.42 ug/cm2 after 48 hours with a slope suggestive of continuing incremental absorption. The amounts remaining on or in the epidermis were similar for both dyes (approx. 1.3 ug/cm2). Comparison of the human in vitro data with historical human in vivo data obtained under application and wear conditions indicated that for HC Blue No. 2 the in vitro receptor fluid concentration alone approximated the Day 1 in vivo value (0.23 ug/cm2) whereas it underestimated the Day 1 in vivo value for HC Blue No. 1 (2.81 ug/cm2). Consideration of the in vitro time course data suggested that incremental absorption of HC Blue No. 2 over time (Days 2-30) in vivo resulted primarily from re-exposure to dye leached from the hair reservoir whereas incremental absorption of HC Blue No. 1 may have resulted, at least in part, from continued mobility of dye in the epidermis.