Hypothesis: the epidermal permeability barrier is a porous medium

Area of Science:

• Dermatology
• Biophysics
• Materials Science

Background:

• The stratum corneum, the outermost layer of the skin, exhibits very low permeability.
• It acts as a crucial barrier against water loss and molecular penetration.
• Previous models conceptualized it as a simple porous medium.

Purpose of the Study:

• To refine the understanding of the stratum corneum's barrier function.
• To propose a detailed model of its physical structure and permeability.
• To elucidate the diffusion mechanisms of solutes within this layer.

Main Methods:

• Conceptual modeling based on existing knowledge of stratum corneum structure.
• Analysis of intercellular lipid membrane phases (solid and liquid crystalline).
• Classification of corneocyte envelope as impermeable.

Main Results:

• The stratum corneum is modeled as a composite of impermeable and permeable regions.
• Intercellular lipid membranes are proposed to exist in both solid (impermeable) and liquid crystalline (permeable) phases.
• The corneocyte envelope is identified as an impermeable component.

Conclusions:

• The proposed model refines previous theories on stratum corneum permeability.
• Understanding the phase behavior of lipid membranes is key to barrier function.
• This model provides a more nuanced view of solute diffusion pathways.