Two methods of estimating stratum corneum thickness using reflectance confocal microscopy were examined, and epidermal thickness measurements at multiple body sites were compared. Measurements of stratum corneum thickness were made using the derivative method, which is based on the rate of change of image intensity as a proxy for keratin concentration, and simple visual analysis of confocal images. To compare epidermal thickness we collected 1491 z-axis stacks of confocal images from 10 body sites in 39 subjects. An artefact associated with the imaging process interfered with the derivative method for stratum corneum thickness, and simple visual analysis is to be preferred. Although some epidermal properties varied by site, the most striking finding was the degree of within-site variation, which accounted for between 50% and 74% of the total variation observed. The majority of this variation was not due to measurement error, and represents genuine topographical irregularity. This fine-scale variation limits the ease of use of reflectance confocal microscopy for quantitative studies of the epidermis and stratum corneum.
