Individual and instrumental variations in irritant patch-test reactions--clinical evaluation and quantification by bioengineering methods.

A major purpose of irritant patch testing is to differentiate between normal, delicate and less sensitive skin. To assess the usefulness of irritant patch testing, knowledge of variation in responses to identical patch tests is essential. In the present study inter- and intra-individual variation in irritant patch test reactions due to sodium lauryl sulphate and nonanoic acid is given when evaluated by traditional visual scoring as well as different non-invasive methods, i.e. measurement of transepidermal water loss, the hydration state of stratum corneum by electrical conductance, cutaneous blood flow by laser Doppler flowmetry, and measurement of skin thickness by 20-MHz ultrasound A-scan. The intra-individual 'site-to-site' variation was considerably less than the inter-individual variation, which is essential to differentiate between persons with delicate and less sensitive skin. Methods used were relevant for this purpose except for the measurement of electrical conductance.