[8] Cellular mechanisms for regulating water and sodium levels (ENaCs) are found in all layers of the epidermis.

Differentiated keratinocytes secrete keratin proteins, which contribute to the formation of an extracellular matrix that is an integral part of the skin barrier function.

Calcium concentration in the stratum corneum is very low in part because those relatively dry cells are not able to dissolve the ions.

This calcium gradient parallels keratinocyte differentiation and as such is considered a key regulator in the formation of the epidermal layers.

[21] Epidermal development is a product of several growth factors, two of which are:[20] The epidermis serves as a barrier to protect the body against microbial pathogens, oxidant stress (UV light), and chemical compounds, and provides mechanical resistance to minor injury.

[25] Lipids arranged through a gradient and in an organized manner between the cells of the stratum corneum form a barrier to transepidermal water loss.

[26][27] The amount and distribution of melanin pigment in the epidermis is the main reason for variation in skin color in Homo sapiens.

The number of melanosomes in the keratinocytes increases with UV radiation exposure, while their distribution remain largely unaffected.

Historically, the role of Merkel cells in sensing touch has been thought to be indirect, due their close association with nerve endings.

However, recent work in mice and other model organisms demonstrates that Merkel cells intrinsically transform touch into electrical signals that are transmitted to the nervous system.

[29] Laboratory culture of keratinocytes to form a 3D structure (artificial skin) recapitulating most of the properties of the epidermis is routinely used as a tool for drug development and testing.