When ultraviolet radiation is absorbed in the skin at the 2 mm depth, the layer is called

• A. Stratum granulosum
• B. Stratum spinosum
• C. Basal cells
• D. Stratum cornium

Answer: (D)

UV energy reaching the skin is largely intercepted by the outer protective barrier of the epidermis. The outermost epidermal layer, the stratum corneum, is made up of dead keratin-filled cells that form a tough, waterproof envelope. This barrier absorbs and attenuates UV radiation, helping to shield the deeper, living cells of the epidermis and dermis from damage. In this context, the layer described at that depth is the stratum corneum, which is why it’s the correct choice. The other epidermal layers—basal cells, spinosum, and granulosum—are deeper and contain living cells, so they aren’t the layer primarily associated with that surface-depth UV interaction.