Hornlagret

Hornlagret, also known as the stratum corneum, is the outermost layer of the epidermis in mammalian skin. It is composed of flattened, dead keratinocytes called corneocytes, which are densely packed with keratin, a tough structural protein. The corneocytes are arranged in multiple layers and are embedded in a lipid matrix that forms a barrier. This barrier is crucial for protecting the body from mechanical stress, chemical damage, and the invasion of pathogens. It also plays a vital role in preventing transepidermal water loss, thereby maintaining skin hydration and overall body fluid balance.

The formation of the stratum corneum is a continuous process called keratinization or cornification. New keratinocytes are generated in the basal layer of the epidermis and then migrate upwards through the epidermal layers, undergoing significant changes in their structure and composition. As they move towards the surface, the cells lose their organelles, including their nucleus and mitochondria, and fill with keratin. Simultaneously, the cells release lipids into the extracellular space, which are essential for barrier function. This process takes approximately 2 to 4 weeks in humans.

The thickness of the stratum corneum varies across different body sites, being thickest on the palms of the hands and soles of the feet, where mechanical stress is greatest. Its appearance can be influenced by various factors, including hydration, age, and environmental conditions. The regular shedding of the outermost corneocytes, known as desquamation, is a normal physiological process that is essential for maintaining the integrity and function of the skin barrier. Disruptions to this shedding process can lead to conditions like dryness, scaling, and increased susceptibility to infections.