The epidermis is the outermost layer of the skin and protects the body from the environment. The epidermis is comprised of the following cells:
- Keratinocytes: Most common types of cells in the epidermis
- Melanocytes: Contain melanin pigment; where melanoma develops
- Langerhans cells: Involved in the immune system in the skin
- Merkel cells: Involved in sensory communication
The epidermal layer comprises five sub-layers that continually rebuild the skin surface. The five sub-layers include:
- Keratin
- Lucid
- Granular
- Spinous
- Basal
The keratinocytes originate in the basal layer and differentiate as they are pushed up to the surface layer and shed in the keratin layer.
The upper-most layer is called the stratum corneum, composed of dead keratinocytes (the most common type of cell in the epidermis). The cells in this layer are identified by their flat shape and are called squamous cells.
The deepest layer is called the stratum basale (also known as basal), where keratinocytes and basal cell carcinoma (BCC) originate.
In the layer between the corneum and basal layers, keratinocytes differentiate as they are pushed up toward the skin's surface and undergo several morphological changes, gradually losing their nucleus and organelles. As the keratinocytes are pushed upward, they flatten (squamous) and become flattened polyhedrons. It is in this layer that cellular changes occur, leading to squamous cell carcinoma (SCC).
BCC and SCC are basal or squamous cells that grow out of control, usually due to DNA damage from the sun's ultraviolet (UV) light. These cancers typically stay in place (do not metastasize) and can be surgically removed. Malignant melanoma (MM) has a very high rate of metastasis (or spreading). Therefore, early detection improves the cure rate.
The images show the different layers of cells in the epidermis and how they differentiate as they move toward the skin's surface from the basal layer.
