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

Examples of stratum corneum in a Sentence

Recent Examples on the Web

Skin has a moisture barrier called the stratum corneum, Kapoor said, which is the topmost skin layer that stops water from leaving the body. —Jocelyn Solis-Moreira, CNN, 7 Apr. 2024

Ceramides comprise nearly 50% of the lipids in the stratum corneum. —Lisa Desantis, Health, 22 Mar. 2024

There are seven layers of skin, and most topical products, such as skincare products, only penetrate the stratum corneum (the outermost layer). —Rachel Murphy, Verywell Health, 1 Mar. 2024

The stratum corneum, the outermost layer of your skin, is also different on and around your lips. —Melanie Rud, SELF, 28 Sep. 2023

In the elephant’s skin, fissures had formed where the stratum corneum dipped into the deeper layer's troughs. —Roni Dengler, Discover Magazine, 2 Oct. 2018

Skin Activator was formulated with the same award-winning science, so its delivery system mimic’s the skin’s natural structure to maximize absorption into the stratum corneum while being gentle. —Celia Shatzman, Forbes, 16 Mar. 2023

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

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