What is commonly referred to as "the skin's barrier"?

The stratum corneum is commonly referred to as "the skin's barrier" because it serves as the outermost layer of the epidermis and is primarily responsible for protecting underlying tissues from external environmental factors. This layer consists of dead keratinized cells that are continuously shed and replaced, creating a resilient and impermeable barrier. The keratin present in these cells provides strength and helps to minimize water loss from the body, while also preventing the entry of pathogens, chemicals, and other harmful substances.

In contrast, the epidermis, which includes the stratum corneum, is the entire outer layer of skin but does not solely define the barrier function. The dermis, located beneath the epidermis, contains connective tissue, blood vessels, and nerves but does not directly contribute to the barrier properties. The subcutaneous layer, which is deeper than the dermis, mainly consists of fat and connective tissue that serve to insulate the body and anchor the skin to underlying structures, but it is not involved in barrier protection. Therefore, the stratum corneum is specifically recognized for its role in safeguarding the skin and regulating moisture levels, making it the key component referred to as "the skin's barrier."