What constitutes the horny layer of the skin?

The horny layer of the skin, also known as the stratum corneum, is primarily composed of dead skin cells. This outermost layer acts as a protective barrier for the underlying layers of the skin and is crucial for maintaining skin hydration and providing a defense against environmental factors such as pathogens and UV radiation. The cells in this layer are flattened and keratinized, meaning they have lost their nuclei and are filled with keratin, a tough protein that helps to waterproof and protect the skin.

Newly formed skin pertains to the deeper layers of the epidermis, where active cell division occurs, and it has not yet reached the stage of keratinization that characterizes the horny layer. Moisturized skin refers to skin that has adequate hydration levels, which is not a defining characteristic of the horny layer itself; rather, it describes the condition of the skin. Skin with active cells indicates layers that are still undergoing cell division and differentiation, which is below the stratum corneum and thus does not relate to the composition of the horny layer. Therefore, the distinction of the horny layer as being made up of dead skin is critical in understanding its function and structure within the skin's overall anatomy.