The outermost layer of skin, the stratum corneum (SC), while primarily acting as a hydrophobic barrier, contains a hydrophilic component. This is because the stratum corneum's intercellular lipid matrix, though mainly hydrophobic, facilitates the passage of both hydrophilic and hydrophobic substances, including water. The presence of water (5–20%) within the stratum corneum further contributes to its hydrophilic properties. Therefore, while predominantly hydrophobic, the stratum corneum displays some hydrophilic characteristics due to water content and pathways within its lipid matrix. The degree of hydrophilicity or hydrophobicity can also be influenced by factors like the sebum and hydrolipidic layer. A water drop's spread on skin indicates its hydrophilicity or hydrophobicity.
- Hydrophilic properties: The stratum corneum's ability to transport water and other hydrophilic substances indicates its hydrophilic nature, albeit limited compared to its hydrophobic properties.
- Hydrophobic dominance: The stratum corneum's primary function is as a protective barrier, mainly achieved through its hydrophobic lipid composition. This hydrophobic nature greatly restricts the penetration of hydrophilic molecules.
- Water content: The stratum corneum contains a notable amount of water (5-20%), adding to its hydrophilic characteristics.
The ability of the stratum corneum to transport both hydrophilic and hydrophobic molecules highlights its complex structure and function, acting as a selective barrier to regulate substance passage into the deeper layers of the skin. Substances like those found in soap can influence the skin's wettability, affecting its hydrophilicity.
