Which skin layer is the primary barrier to diffusion, often described as the rate-limiting barrier for percutaneous absorption?

Which skin layer is the primary barrier to diffusion, often described as the rate-limiting barrier for percutaneous absorption?

• A. Dermis
• B. Stratum Corneum
• C. Epidermis
• D. Hypodermis

Answer: (B)

The stratum corneum is the primary barrier to diffusion. This outermost layer of the epidermis is made of corneocytes embedded in a lipid-rich matrix, forming a tight, brick-and-mortar barrier that greatly resists both water loss and chemical penetration. Because a permeant must partition into and then diffuse through this lipid-rich layer before reaching deeper skin tissues or systemic circulation, the stratum corneum largely determines the rate of percutaneous absorption. The underlying dermis and hypodermis are not the main barriers; they influence later steps once the barrier is crossed. The stratum corneum’s properties—lipid composition, thickness, and hydration—therefore set the pace for diffusion through the skin.

The stratum corneum is the primary barrier to diffusion. This outermost layer of the epidermis is made of corneocytes embedded in a lipid-rich matrix, forming a tight, brick-and-mortar barrier that greatly resists both water loss and chemical penetration. Because a permeant must partition into and then diffuse through this lipid-rich layer before reaching deeper skin tissues or systemic circulation, the stratum corneum largely determines the rate of percutaneous absorption. The underlying dermis and hypodermis are not the main barriers; they influence later steps once the barrier is crossed. The stratum corneum’s properties—lipid composition, thickness, and hydration—therefore set the pace for diffusion through the skin.