korneum

Korneum is the term used in some medical and linguistic contexts to refer to the outermost layer of the epidermis, scientifically known as the stratum corneum. The word derives from Latin corneus, meaning hornlike, reflecting its protective, horn-shaped character. In many dermatology texts the two terms are used interchangeably.

Anatomy: The layer comprises corneocytes, flattened, largely enucleated keratin-filled cells, arranged in laminated sheets. They are embedded in a lipid-rich extracellular matrix that forms the mortar in the bricks-and-mortar analogy of skin structure. This barrier is cornified and highly resistant to physical and chemical challenges.

Function: The stratum corneum serves as the principal barrier of the skin. It minimizes transepidermal water loss, helps prevent chemical and microbial intrusion, and contributes to the skin's mechanical protection and overall homeostasis. Its integrity depends on proper lipid composition, including ceramides, cholesterol, and free fatty acids.

Variation and turnover: Thickness varies by site, typically 10–20 micrometers, with regions such as the palms and soles showing greater thickness. The corneum is continuously renewed as basal keratinocytes differentiate through the epidermal layers and become corneocytes before desquamating over about 2–4 weeks.

Clinical relevance: Disorders affecting the korneum, or its lipid matrix, include dry skin, eczematous dermatitis, ichthyosis, and psoriasis. Barrier impairment can increase transepidermal water loss and irritant sensitivity; conversely, excessive keratinization can cause hyperkeratosis. Treatments often focus on restoring lipid content and promoting normal desquamation via moisturizers and, where appropriate, keratolytics.