What skin layer is primarily responsible for the skin's barrier function?

The epidermis is primarily responsible for the skin's barrier function. This outermost layer of the skin serves as the first line of defense against environmental aggressors, such as pathogens, chemicals, and physical injury. Its structure includes several layers of cells, notably keratinocytes, which produce keratin—a protein that helps to form a protective barrier.

Within the epidermis, the stratum corneum, the outermost layer, is especially critical for barrier function. It consists of dead skin cells that are tightly packed and continually shed, creating a protective layer that minimizes water loss and prevents the entry of harmful microorganisms. This barrier also plays a significant role in the skin's overall hydration and maintains its integrity.

The dermis, hypodermis, and subcutaneous layer, while crucial for other functions like support, nourishment, and thermoregulation, do not serve the primary purpose of creating a barrier to the external environment in the way that the epidermis does.