stratum corneum

noun

stratum cor·​ne·​um -ˈkȯr-nē-əm 

: the outermost layer of the epidermis that consists of keratin-rich corneocytes connected by desmosomes and embedded in a matrix of lipids (such as ceramides and cholesterol) arranged in bilayers and that regulates skin permeability, maintains hydration, provides structural integrity, and acts as a protective barrier (as against UV radiation, pathogens, and toxins)

Note: In humans, the stratum corneum is typically 12 to 20 cell layers thick but may be over 50 layers thick in the soles of the feet and less than 9 layers thick on the eyelids. The outer layers are continually shed with one corneocyte cell layer typically sloughed off every day as desmosomes are enzymatically broken down.

The stratum corneum barrier relies predominantly on the extracellular matrix, where lamellar bilayers block the outflow of water into the environment … .

—Peter M. Elias et al.

A primary function of the stratum corneum is to protect the underlying tissue from environmental injury.

—Discover

Example Sentences

Recent Examples on the Web

As a result, the uppermost layer of skin, called the stratum corneum, is removed (don’t worry, it’s made up of mostly skin cells that are already dead) and as skin heals, a new layer is formed with a brighter, firmer look. —Brian Underwood, Women's Health, 15 Mar. 2023

In addition to reducing acne-causing bacteria, azelaic acid has gentle exfoliating properties that can help remove dead skin cells on the very outer layer of the skin, the stratum corneum, leading to a smoother and brighter complexion, says Dr. Shirazi. —Sarah Jacoby, SELF, 22 Mar. 2022

Unlike the rest of our skin, many areas of the lips do not have a stratum corneum (a.k.a. the top layer of skin), Dr. Friedman points out. —Women's Health, 27 Jan. 2023

The outermost layer of skin—called the stratum corneum—is likely a single, continuous layer stretched over the stratum basale, a deeper layer of skin that ripples with bumps that create miniature ridges and valleys. —Roni Dengler, Discover Magazine, 2 Oct. 2018

Again, almost all potential benefits of steaming your face, including product absorption, go back to the stratum corneum softening up. —Mara Santilli, SELF, 28 Feb. 2022

Most of the damage, though, occurs at the stratum corneum, or the outermost layer of the skin, which turns white, indicating that the peroxide is breaking down protein and fats. —Sudiksha Kochi, USA TODAY, 5 Feb. 2022

As the skin is the primary interface between our body and the external environment, its most critical role is to provide a strong physiological barrier, which is mediated by the outermost layer of the epidermis, the stratum corneum. —Alex Zhavoronkov, Forbes, 27 Apr. 2021

Across Instagram, Twitter, and TikTok, skin care pros and enthusiasts have switched their focus from instant-gratification products like acids and peels to the somewhat unsexy stratum corneum (the technical term for your skin moisture barrier). —Bella Cacciatore, Glamour, 22 Jan. 2021

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Word History

Etymology

New Latin, literally, horny layer

First Known Use

1857, in the meaning defined above

Medical Definition

stratum corneum

noun

plural strata cornea

: the outer more or less horny part of the epidermis consisting chiefly of layers of dead flattened nonnucleated cells filled with keratin