We investigated the absorption of a commercial [14C]-PPD- containing oxidative dark-shade hair dye in human volunteers as well as in vitro using human or pig ear skin. The hair of eight male volunteers was cut to a standard length, dyed, washed, dried, clipped and collected. Hair, washing water, materials used in the study and a 24-h scalp wash were collected for determination of radioactivity. Blood, urine and faeces were analysed up to 120 h after hair dyeing. An identical [14C]-PPD-containing hair dye formulation was applied in vitro for 0.5 h to human and pig ear skin, and radioactivity was determined in skin compartments after 24 h. In humans, the recovery rate was 95.7±1.5% of the applied radioactivity. Washing water, cut hair, gloves, paper towels, caps or scalp wash contained a total of 95.16±1.46% of the applied [14C]. Absorbed radioactivity amounted to 0.50±0.24% in the urine and 0.04±0.04% in the faeces, corresponding to a mean of 7.0±3.4 mg [14C]-PPD-equivalents absorbed. Within 24 h after application, most of the radioactivity was eliminated. The Cmax of [14C]-PPD-equivalents in the plasma was 0.087 μgeq/ml, the Tmax was approximately 2 h, and the mean the AUC0-12h was 0.67 μgeqh/ml. In vitro tests in human or pig skin found total absorbed amounts of 2.4±1.6% (10.6±6.7 μgeq/cm2) or 3.4±1.7% (14.6±6.9 μgeq/cm2), respectively. Percentage-based in vitro results were considerably higher than corresponding in vivo data, whereas, in units of μg/cm2, they corresponded to a total absorbed amount of 7.40 or 10.22 mgeq for human or pig skin, respectively. All results suggested that hair dyeing with oxidative hair dyes produces minimal systemic exposure that is unlikely to pose a risk to human health. © 2004 Elsevier Ltd. All rights reserved.