# In Vivo Assessment of Water Content, Trans-Epidermial Water Loss and Thickness in Human Facial Skin
## 4 Results
### Anatomical Variations of Skin Thickness  
The values reported in Table 1 indicate that the stratum corneum and epidermis accounted, together, only for a small fraction (\(<\)8%) of the full skin thickness, whereas the bigger part was taken up by the dermis, as one would expect [2,3]. The total thickness was therefore determined, for the most part of it, by the dermal thickness, and the results indicate that this was highest in the chin and nose regions (Tables 1 and 3c; Figure 8c), which in fact formed a cluster (Figure 9c). Conversely, the dermis was thinnest in the lips and neck, which formed another cluster. The third cluster, with thickness values in-between the previous two, was composed of the forehead and cheeks.  
Figure 8: Box-plots/strip-plots of the thickness by skin layer and facial area.  
Figure 7: Cluster analysis on the distribution of TEWL returned only one cluster of statistically indistinguishable areas: neck and nose.  
As for the stratum corneum, this was thicker in the lips and nose than in the other face regions (Tables 1 and 3a; Figure 8a). The cluster analysis confirmed that there were in fact two clusters: one formed by lips and neck and the other by the remaining regions.  
Interestingly, whereas lips and neck were the regions with the thinnest dermis, they were also the ones with the thickest epidermis (Tables 1 and 3b; Figure 8b). Additionally, the epidermis clustered exactly the same way as the dermis, but the clusters had a different ranking in terms of thickness, as shown in Table 1, Figure 9b).  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{4}{c}{**(a) Stratum Corneum**} \\ \hline  & **Chin** & **F’head** & **Lips** & **Neck** & **Nose** \\ \hline Cheeks & \(6.2\times 10^{-1}\) & \(8.7\times 10^{-2}\) & \(1.7\times 10^{-3}\) & \(5.3\times 10^{-5}\) & \(7.3\times 10^{-1}\) \\ Chin & – & \(2.9\times 10^{-1}\) & \(1.1\times 10^{-3}\) & \(4.6\times 10^{-5}\) & \(8.5\times 10^{-1}\) \\ F’head & – & – & \(8.0\times 10^{-6}\) & \(4.3\times 10^{-8}\) & \(1.6\times 10^{-1}\) \\ Lip & – & – & – & \(3.5\times 10^{-1}\) & \(8.4\times 10^{-4}\) \\ Neck & – & – & – & – & \(8.1\times 10^{-6}\) \\ \hline \multicolumn{4}{c}{**(b) Epidermis**} \\ \hline  & **Chin** & **F’head** & **Lips** & **Neck** & **Nose** \\ \hline Cheeks & \(8.7\times 10^{-6}\) & \(4.8\times 10^{-1}\) & \(5\times 10^{-12}\) & \(5\times 10^{-12}\) & \(9.3\times 10^{-5}\) \\ Chin & – & \(1.1\times 10^{-4}\) & \(2.7\times 10^{-2}\) & \(3.1\times 10^{-3}\) & \(5.6\times 10^{-1}\) \\ F’head & – & – & \(8.7\times 10^{-9}\) & \(1.7\times 10^{-9}\) & \(1.6\times 10^{-3}\) \\ Lip & – & – & – & \(2.6\times 10^{-1}\) & \(2.8\times 10^{-3}\) \\ Neck & – & – & – & – & \(1.9\times 10^{-4}\) \\ \hline \hline \multicolumn{4}{c}{**(c) Dermis**} \\ \hline  & **Chin** & **F’head** & **Lips** & **Neck** & **Nose** \\ \hline Cheeks & \(7.6\times 10^{-2}\) & \(7.7\times 10^{-1}\) & \(9.3\times 10^{-8}\) & \(5\times 10^{-12}\) & \(6.3\times 10^{-5}\) \\ Chin & – & \(8.2\times 10^{-8}\) & \(8\times 10^{-14}\) & \(2\times 10^{-22}\) & \(6.9\times 10^{-1}\) \\ Forehead & – & – & \(1.3\times 10^{-9}\) & \(1\times 10^{-15}\) & \(2.8\times 10^{-4}\) \\ Lip & – & – & – & \(7.9\times 10^{-1}\) & \(6\times 10^{-14}\) \\ Neck & – & – & – & – & \(2\times 10^{-19}\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Thickness of the stratum corneum, epidermis and dermis: results of the pairwise comparisons (\(p\)-value) between the six facial areas. Highlighted figures indicate significant differences (\(\alpha^{*}=3.3\times 10^{-3}\)).  
Figure 9: _Cont._