The Epidermis: The Body’s First Line of Defense

For vertebrates, epidermis is the outer layer of the skin. It is a non-vascular layer that covers the dermis. Melanin is also produced in this layer. It is the chemical responsible for skin color or pigmentation.

This layer is thickest at the soles and palms—about 1.5 mm. It is thinnest on the eyelids at less than 0.05 mm. It practically covers most of the internal organs, muscles, blood vessels and nerves to protect them from trauma. It is amazing how it naturally gets thicker in body parts that need more protection.

The epidermis is a wonderful part of the body because it is made of both living and dead cells. It has five layers. Starting from the outermost, they are the stratum corneum, stratum licidum, stratum granulosum, stratum spinosum, and stratum basale.

The lower layers form columns that gradually change and replace the upper layers. As the cells go up, they start to form flat bodies. Eventually, they die, forming the “skin”, which is visible to the eyes—the stratum corneum.

Dead skin cells are regularly replaced, usually once in every two weeks. The body naturally discards dead skin cells but in unnoticeable amounts. This is how the epidermis functions as a cell-renewal mechanism of the body.

The epidermis also serves as protection from external radiation. Instead of completely absorbing harmful ultraviolet rays, the epidermis has a 3-way action of diffusing it. First, the stratum corneum reflects most of the rays. Secondly, melanin absorbs some of the radiation. And finally, the skin spreads the radiation in itself so that it won’t penetrate the body.

If the epidermis is healthy and undamaged, it is waterproof. It allows selective passage of substances through the pores. The oil emulsion of the skin prevents harmful microbes from entering. This layer also has white blood cells that fight bacteria and other causes of infection.