Understanding the Epidermis

The Anatomy and Function of the Skin's Outermost Layer

The epidermis is the outermost layer of the skin. The thickness of the epidermis varies depending on where on the body it is located. It is at its thinnest on the eyelids, measuring just half a millimeter, and at its thickest on the palms and soles at 1.5 millimeters.

A woman caressing the skin of her knee
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The Anatomy of Skin

The skin's anatomy is composed of three layers: the epidermis, the dermis, and subcutaneous tissue. These layers are home to sweat glands, oil glands, hair follicles, blood vessel, and certain vital immune cells.

Functions of the Epidermis

The epidermis acts as a barrier that protects the body from ultraviolet (UV) radiation, harmful chemicals, and pathogens such as bacteria, viruses, and fungi.

Historically, it was thought that the function of the epidermis was to regulate fluid and protect the body from mechanical injury. In recent years, we've come to understand that it is a complex system that plays a key role in how the immune system communicates and target defense.

Within the epidermis are several distinct layers, consisting of (from bottom to top):

  • Stratum basale, also known as the basal cell layer, is the innermost layer of the epidermis. This layer contains column-shaped basal cells that are constantly dividing and being pushed toward the surface. The stratum basale is also home to melanocytes that produce melanin (the pigment responsible for skin color). When exposed to the sunlight, melanocytes produce more melanin to better protect the skin from UV exposure. Abnormalities in the development of these cells can lead to melanoma, the most deadly type of skin cancer.
  • Stratum spinosum also referred to as the squamous cell layer, is the thickest layer of the epidermis located just above the basal layer. These are composed of basal cells that have matured into squamous cells, known as keratinocytes. Keratinocytes are responsible for producing keratin, a protective protein that makes up skin, nails, and hair. The squamous layer is also home to Langerhans cells which attach themselves to foreign substances as they infiltrate the skin. It is also responsible for synthesizing cytokines, a type of protein that helps regulate the immune response.
  • Stratum granulosum is made up of keratinocytes that have moved up from the squamous layer. As these cells move closer toward the skin's surface, they begin to flatten and stick together, eventually drying and dying out. 
  • Stratum corneum is the outermost layer of the epidermis. It consists of 10 to 30 layers of dead keratinocytes that are constantly being shed. Shedding of these cells slows significantly with age. The complete cell turnover, from basal cell to stratum corneum, takes around four to six weeks for young adults and about a month and a half for older adults.
  • Stratum lucidum only exists on the palms of the hands and soles of the feet. It consists of four layers rather than the typical four.

Conditions Involving the Epidermis

The epidermis can be impacted by more than just injury. This outermost layer is subject to both genetics and external forces that contribute to the aging of this skin. These factors include smoking, alcohol, and excessive UV exposure, all of which contribute to the development of wrinkles, sunspots, and the uneven thickening or thinning of the skin.

The epidermis is also where rashes and blisters appear, caused by everything from infections and allergies to diseases and toxins. It is also the origin of both non-melanoma and melanoma skin cancers, and where certain diseases like diabetes and lupus can manifest with an array of dermatological symptoms.

Penetration of the epidermis can cause infections that the body can otherwise defend against. These include diseases caused by insect or animal bites, as well as those pathogens that enter the body through open sores, cuts, abrasions, or needlestick injury. 

Frequently Asked Questions

  • What are the five layers of the epidermis?

    The five layers of the epidermis are: 

    • Stratum basale
    • Stratum spinosum
    • Stratum granulosum
    • Stratum corneum
    • Stratum lucidum
  • What is the role of the epidermis?

    The epidermis, or skin, provides a protective barrier against UV radiation, chemicals, and microorganisms, including bacteria, viruses, and fungi.

  • Do humans shed their skin?

    Yes and no. Humans do not shed their skin in the same way a snake does, but our skin cells are constantly being replaced. Skin cells live for about four to six weeks in young adults, and little longer than six weeks in older adults. Once a skin cell dies, it works its way to the outer layer of the epidermis, where it is shed.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Oltulu P, Ince B, Kokbudak N, Findik S, Kilinc F. Measurement of epidermis, dermis, and total skin thicknesses from six different body regions with a new ethical histometric technique. Turk J Plast Surg 2018;26:56-61

  2. U.S. National Library of Medicine. MedlinePlus. Aging changes in skin.

  3. American Society of Clinical Oncology. Melanoma: introduction.

Additional Reading
  • Tan, S.; Roediger, B.; and Weninger, W. "The Role of Chemokines in Cutaneous Immunosurveillance."Immunology and Cell Biology. 2015; 93(4):337-46.

By Heather L. Brannon, MD
Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.