Skin is essential for protecting the body in different ways. The three layers of skin—epidermis, dermis, and hypodermis—are briefly described below and are illustrated in diagrams and a photograph.
Epidermis: The uppermost or top layer of skin is a thin layer, only about as thick as the roof of a blister, or a couple of sheets of paper. The “basal layer” of cells, aptly named because of its location at the base of the epidermis, separates the epidermis from the dermis and contains basal cells, melanocytes (pigment cells), Merkel cells, and a few other cells.
Above the basal layer (closer to the skin surface) is a thick layer of squamous cells, also referred to as keratinocytes because of their production of keratin (the protein found in hair and finger/toenails). When squamous cells die, they become dried up in a mummified-like fashion to form a dead layer of keratin at the very top surface of the skin. The keratin layer varies in thickness, being very thick on the soles and palms, and very thin in other areas such as the eyelids. When keratin sloughs off, it resembles white flakes, something we have all seen on the surface of our skin.
Dermis: The middle layer of skin consists of dense connective tissue and important proteins needed to support the skin. Because of its denseness, this layer of skin in animals has been used to produce leather for thousands of years! The dermis houses blood vessels, nerves, lymphatics, hair follicles with their lubricating sebaceous glands, and tiny muscles which can contract to give us “goosebumps.”
Hypodermis: This layer is below the skin and is rich in fat and other loose connective tissue. By acting as a sort of lubricant, it allows the skin limited movement over the underlying structures such as muscles. Were it not for this important layer, every bump of the skin could result in vessels and tissue being torn or ruptured.
All photographs and diagrams are intended for informational purposes only and are not intended to be used for diagnosis. A dermatologist should be consulted for examination and diagnosis of skin lesions.
Diagram 1. In this diagram, one can see the epidermis (labeled on left side), dermis (labeled in the center), and the hypodermis at the bottom. The basal layer (illustrated as a single layer of white cells) separates the epidermis from the dermis.
Diagram 2. Note that the melanocyte (pigment cell) illustrated in the basal layer has “octopus-like tentacles” that extend up into the epidermis. In this diagram, the squamous cells are labeled as “keratinocytes.” As these cells approach the skin surface, they become flattened, and eventually form a dead layer of keratin.
Diagram 3. This is a photo of a skin biopsy as viewed under the microscope. At the top of the photo, the dead layers of keratin can be seen peeling off the skin surface. This is normal, as dead keratin is continually replaced when underlying squamous cells die and reach the skin surface. Below this is the thin layer of epidermis (the darker purple layer) with its many squamous cells (basal layer is not readily apparent in this photo). In contrast, the dermis (lighter purple layer) consists of dense fibrous tissue. The large nest of dark purple cells in the middle of the dermis consists of cancerous basal cells; hence this is a biopsy of a basal cell carcinoma.