Which type of epidermal layer provides a barrier to water loss?

The stratum corneum is the outermost layer of the epidermis and plays a crucial role in providing a barrier to water loss. It is composed of dead, flattened keratinocytes that are rich in keratin, a fibrous protein that enhances the barrier properties of the skin. This layer is particularly effective at retaining moisture within the skin due to its structure, which minimizes permeability to water. The presence of lipids between the cells in the stratum corneum also contributes to its ability to prevent transepidermal water loss and maintain hydration levels in the underlying layers of the skin.

The other layers, while essential for different functions, do not provide the primary barrier to water loss. The stratum lucidum is found only in certain areas of thick skin and helps with friction but does not have the same water-retention properties. The stratum granulosum contributes to keratinization but is lower in the epidermis than the stratum corneum, meaning it cannot solely guard against water loss. The stratum basale is primarily involved in cell division and the generation of new skin cells, rather than in providing a barrier.