What is the main protective function of the stratum corneum?

• A. It produces melanin to protect against UV.
• B. It forms a barrier to protect against environmental aggressors and reduces transepidermal water loss.
• C. It is the primary source of sebum.
• D. It regenerates every 2 hours.

Answer: (B)

The main protective job of the stratum corneum is to act as a barrier that shields the tissues beneath from environmental irritants and minimizes water loss. This outermost epidermal layer is made of dead cells called corneocytes embedded in a lipid-rich matrix, creating a brick-and-mortar structure that forms a waterproof seal. By limiting transepidermal water loss, it helps keep skin hydrated and intact, while also helping prevent microbes and pollutants from penetrating deeper layers.

Melanin production occurs in melanocytes in the deeper epidermal layers, not in the stratum corneum. Sebum is produced by sebaceous glands in the dermis and released onto the skin surface, not by the stratum corneum. The turnover of skin cells is not as fast as every two hours; the process from basal layer to surface typically takes about a month, though it can vary with age and condition.