What is the rate-limiting barrier in absorption of drugs through the skin?

What is the rate-limiting barrier in absorption of drugs through the skin?

• A. Stratum Corneum (outer layer of dead epithelial cells)
• B. Dermis
• C. Hypodermis
• D. Hair follicles

Answer: (A)

The stratum corneum is the rate-limiting barrier to transdermal drug absorption. This outermost epidermal layer is made of dead keratinized cells embedded in a lipid-rich matrix, forming a tight, water-repellent barrier. Diffusion through this lipid-packed layer is the slowest step for most drugs, so it largely controls how quickly a compound can penetrate the skin and reach systemic circulation. Deeper layers like the dermis and hypodermis are reached more easily once past the stratum corneum, and while hair follicles and sweat glands can provide alternate routes, they typically contribute only a small portion of overall absorption.

The stratum corneum is the rate-limiting barrier to transdermal drug absorption. This outermost epidermal layer is made of dead keratinized cells embedded in a lipid-rich matrix, forming a tight, water-repellent barrier. Diffusion through this lipid-packed layer is the slowest step for most drugs, so it largely controls how quickly a compound can penetrate the skin and reach systemic circulation. Deeper layers like the dermis and hypodermis are reached more easily once past the stratum corneum, and while hair follicles and sweat glands can provide alternate routes, they typically contribute only a small portion of overall absorption.