Racial differences in acute and cumulative skin irritation responses between Caucasian and Asian populations

One of the more confounding issues in dermatology relates to racial differences in susceptibility of human subjects to skin reactions resulting from chemical or physical trauma. There is some historical evidence to support a greater resistance of Black versus Caucasian populations to skin irritation or skin allergy, likely due to a more substantial barrier to chemical penetration. A heightened sensitivity among Asian subjects (versus Caucasians) has been suggested; however, the evidence published to date is not very compelling. Part of the difficulty has been the lack of concurrent studies. Previously, we had examined the elicitation of mild skin irritation responses to relatively high concentrations of test chemicals, using a novel acute irritation patch test protocol for the assessment of chemical skin irritation potential. Caucasian and Chinese subjects were exposed under patch for up to 4 h to chemicals of varying irritation potency. No significant differences were seen in the cumulative incidence of positive responders to any of the test chemicals across the 2 populations, even when the subjects were preselected for sensitivity to lactic acid stinging. To extend these findings, the focus of the current investigation was to compare directly skin irritation responses between Caucasian subjects and different subpopulations of Asian subjects (Chinese, Japanese) to determine if any significant differences in response patterns would emerge. 2 separate studies were conducted. The initial study compared Caucasian and Japanese subjects for responses to 20% sodium docecyl sulfate (SDS), 10% acetic acid, 100% octanoic acid, 100% decanol, and water. In addition, a concurrent test was conducted comparing 14-day cumulative irritation responses to varying concentrations (0.025% to 0.3%) of SDS. In both the acute and cumulative irritation tests, the Japanese subjects showed a tendency to respond faster than the Caucasian subjects. Significant differences in response were seen at several chemical exposure time points in the acute irritation test, and with the lowest concentration of SDS (0.025%) in the cumulative irritation test. A repeat of this exact study protocol was then conducted among Caucasian, Japanese, and Chinese subjects. In this 2nd study, no differences were seen in the acute or cumulative irritation responses between the Japanese and Caucasian subjects. The Chinese subjects showed a heightened response to 10% acetic acid (after 4 h of exposure), but otherwise displayed a similar response profile in the acute irritation test. They showed a slower and less severe response in the cumulative irritation test compared to the Caucasian or Japanese subjects. These divergent results underscore the difficulty in ascribing true population-based differences in skin reactivity based upon studies in limited subject populations. It may be possible to detect differences in individual studies, but repeal testing may fail to confirm a consistent trend. These findings may be indicative of the wide variation in skill responsiveness across human subjects in general.