Which epidermal layer forms the outermost protective barrier of the skin?

• A. Stratum corneum
• B. Stratum lucidum
• C. Stratum granulosum
• D. Stratum basale

Answer: (A)

The outermost protective barrier of the skin is formed by the stratum corneum. This topmost epidermal layer consists of many flattened, dead keratinocytes called corneocytes that are filled with keratin and held together by lipids. These cells are produced in the deeper layers, keratinize as they move upward, lose their nuclei, and form a tough, waterproof shield. Because the corneum is continuously shed and replaced from below, it effectively blocks water loss and invasion by microbes while providing mechanical protection.

In thick skin, there is a thin additional clear layer called the stratum lucidum just beneath the corneum, but the outermost barrier remains the stratum corneum.