ABSTRACT
The human nail is approximately 100 times thicker than the stratum corneum, and both are rich in keratin. However, they exhibit some physical and chemical differences (11,12). The nail possesses high sulphur content (cystine) in its hard keratin domain, whereas the stratum corneum does not. The total lipid content of the nail ranges from 0.1% to 1%, as opposed to approximately 10% for the stratum corneum. This suggests that the role of the lipid pathway in the nail plate is probably of much less importance than that in the stratum corneum. The human nail acts like a hydrophilic gel membrane, while the stratum corneum acts like a lipophilic partition membrane.
