Absorption through the skin: theory, in vitro techniques and their applications

Area of Science:

• Toxicology
• Dermatology
• Pharmacokinetics

Background:

• Chemical exposure via skin contact necessitates accurate percutaneous absorption assessment for risk evaluation.
• The stratum corneum, the skin's outer layer, is the primary barrier to chemical diffusion, a passive process.
• Understanding the physical chemistry of skin absorption is vital for predicting chemical behavior.

Purpose of the Study:

• To highlight the importance of in vitro skin permeability measurements.
• To emphasize the utility of diffusion cells in studying the physical chemistry of skin absorption.
• To advocate for the use of human skin in vitro for accurate absorption assessments.

Main Methods:

• Utilizing in vitro diffusion cells with human skin samples.
• Measuring skin permeability to determine the rate-limiting diffusion step across the stratum corneum.
• Establishing physical chemistry parameters governing percutaneous absorption.

Main Results:

• In vitro measurements in diffusion cells provide meaningful data on skin permeability.
• The passive diffusion across the stratum corneum is well-characterized.
• Human skin in vitro is the most relevant model for assessing absorption across diverse chemicals.

Conclusions:

• In vitro diffusion cell studies with human skin are essential for accurate risk assessment of chemical exposure.
• The physical chemistry of skin absorption can be effectively studied using these methods.
• Human skin offers a superior in vitro model compared to animal models for percutaneous absorption studies.