Sonography is a well-known non-invasive technique for skin imaging, used primarily to assess skin lesions, such as tumours, prior to surgery, but also to monitor oedema and inflammatory processes. Commercially available scanners have limited image resolution which complicates analysis especially when very different echo-densities coexist. In this work we propose a three-dimensional (3D) analysis reconstruction of the skin bi-dimensional echo image to better define, compare and quantify different echo-density structures. Images from the volar forearm were taken using a 20-MHz ultrasonograph (Dermascan C, Cortex Technology, Denmark) in 6 young healthy volunteers (aged 18-30) of both sexes. We compared non-treated skin with skin hydrated with a 5% solution of glycerine in an occlusive patch for 24hours. All procedures complied with the principles of the Helsinki declaration and subsequent amendments. The probe was placed on the skin in a fixed standard position, with the echo recorded at a velocity of 1580 m/s, to obtain a two dimensional-image. The colour image was converted to a grey scale image for further analysis. From the scans, 3D length-thickness-echo intensity representations were created. These representations allowed the calculation of the surface area (SA, expressed in square arbitrary units) and the volume under the surface (VUS, expressed in cubic arbitrary units) of the epidermal and dermal layers, normalized for layer thickness. The more echogenic epidermal layer showed higher mean relative VUS and SA relative to the more homogenous dermal layer (VUSepidermis 0.093 ± 0.096; VUSdermis: 0.042 ± 0.033; SAepidermis: 1.0 ± 0.005; SAdermis: 0.144 ± 0.001). A decrease in the echo was observed in hydrated skin, for both the epidermis and dermis. Consequently, the VUSepidermis decreased from 0.215 ± 0.250 to 0.041 ± 0.075; and VUSdermis from 0.033 ± 0.050 to 0.009 ± 0.012. No changes were observed for the SA, however. Under these experimental conditions, higher echogenicity is better revealed by higher VUS, but not SA. These 3D representations and quantitative parameters seem to offer a useful potential to further explore sonography as a quantitative instrument in experimental dermatology.