Anatomy of the Epidermis

The skin is made up of three layers:

The epidermis (the uppermost layer of skin) is an important system that creates our skin tone, while the dermis (the middle layer) contains connective tissue, hair follicles, and sweat glands that help regulate the integrity and temperature of our the skin. The deeper hypodermis is made up of fat and even more connective tissue.

Portrait of a Young Womans Back with Freckles
Rochelle Brock / Refinery29 for Getty Images / Getty Images

Within the epidermis, there are four major layers of cells (called keratinocytes) that provide the skin its structural supports, as well as one layer specific to the soles and palms. Keratinocytes within the epidermis begin dividing in the bottom layer, pushing already formed cells into the upper layer. As cells move higher, they gradually flatten and die off.

Stratum Basale

The bottom layer of the epidermis is called the stratum basale. This layer contains one row of column-shaped keratinocytes called basal cells. These cells are constantly dividing and pushing already-formed cells towards the skin's surface. As basal cells move into the upper layers, they will also flatten, die, and be shed to make room for newer cells.

Melanocytes, the cells that produce melanin (the pigment which provides your skin its color), are also found in this layer.

Stratum Spinosum

The spinosum layer lies just over the stratum basale and is only about five to 10 cells thick. Cells that move into the spinosum layer (which is also known as the prickle cell or squamous cell layer) naturally morph from its initial columnar shape into a polygonal (multi-sided) one. 

Cells in this layer are responsible for making keratin, the fibrous protein that gives the skin, hair, and nails their hardness and water-resistant properties.

Stratum Granulosum

The cells in the stratum granulosum, or granular layer, have lost their nuclei and appear as flattened cells containing dark clumps of cytoplasmic material. There is a lot of activity in this layer as keratin proteins and lipids work together to create many of the cells responsible for the skin's protective barrier.

Stratum Lucidum

The stratum lucidum layer is only present in the thicker skin of the palms and soles. Its main function is to reduce friction between the stratum corneum and stratum granulosum. The name itself comes from the Latin for "clear layer," which describes the transparency of the cells themselves.

Stratum Corneum

The cells in the stratum corneum layer are known as corneocytes (or horny cells). These cells have flattened out and are considered dead. Composed mainly of keratin proteins, corneocytes provide structural strength to the stratum corneum but also allow for the absorption of water. They serve as an effective barrier to any chemicals that might harm the living cells just beneath them.

A Close-Up of the Stratum Corneum

The structure of the stratum corneum may look simple, but it plays a key role in maintaining the structural integrity and hydration of the skin. it not only ensures the continued production of new skin cells but affords the body vital protections against viruses, bacteria, parasites, and any other form of pathogen or toxin.

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