Non-invasive assessment of stratum corneum structure and function

Area of Science:

• Dermatology
• Biophysics
• Cosmetic Science

Background:

• The stratum corneum is crucial for skin barrier function.
• Understanding its properties is vital for clinical and cosmetic applications.
• Existing methods for in situ analysis have limitations.

Purpose of the Study:

• To review and discuss in situ methods for studying the stratum corneum.
• To highlight the application of these methods in clinical problems and cosmetic science.
• To evaluate current techniques for measuring stratum corneum thickness, barrier function, mechanical properties, and desquamation.

Main Methods:

• High-frequency pulsed ultrasound for skin thickness and component measurement.
• Transepidermal water loss (TEWL) measurements for barrier function assessment.
• Profilometry and mechanical testing for stratum corneum deformability and extensibility.
• Corneocyte collection (passive and forced desquamation) and dansyl chloride fluorescence for desquamation and kinetics.

Main Results:

• Ultrasound can measure epidermal and stratum corneum thickness, potentially varying with hydration.
• Mechanical testing correlates with reduced flexural ability in ichthyotic disorders.
• Various methods assess hydration changes and desquamation rates, though some are laborious.

Conclusions:

• A range of in vivo techniques exist for evaluating stratum corneum properties.
• These methods are applicable to clinical dermatology and cosmetic product development.
• Further refinement and validation are needed, but current tests are valuable for understanding stratum corneum biology and pharmacology.