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

But by bypassing the stratum corneum, spicules promote deeper penetration of active ingredients—ultimately promoting more efficacy from your skin-care routine. —Emily Orofino, Vogue, 11 Mar. 2025

Drink plenty of fluids to keep the stratum corneum (outermost skin layer) healthy and hydrated.19 Prevention Tips Staying out of the sun and avoiding UV light exposure is, by far, the most critical prevention tip. —Christopher Bergland, Verywell Health, 4 Feb. 2025

The top layer mimics the outermost part of the skin, known as the stratum corneum. —Krittika Goyal, The Conversation, 29 Jan. 2025

Don't overdo it: Stick to a facial cleansing routine, but remember that cleaning too often can disrupt the stratum corneum, causing more sebum production. —Mark Gurarie, Health, 1 Jan. 2025

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