Assessment of skin irritancy: measurement of skin fold thickness

It is desirable to use more objective methods than visual scoring for the assessment of skin irritancy reactions. The edema, or fluid accumulation in the exposed skin sites, can be accurately measured by a caliper and this alternative method of assessment is evaluated from different aspects. Sodium lauryl sulfate (SLS) and non-anoic acid in different concentrations were applied daily to human and animal (rabbit and guinea pig) skin, and a dose-response relationship established. Higher concentrations of the irritants induced an earlier response. With 5% SLS as the test substance and the increase in skin fold thickness as the single parameter of skin irritancy, the guinea pig was found to be less reactive than rabbit and man. Measurement techniques, reproducibility and advantages and disadvantages with different animal models are discussed.