Histologic image showing a section of epidermis. Stratum granulosum labeled near center.
The stratum granulosum (or granular layer) is a thin layer of cells in the epidermis.Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in this layer. These cells contain keratohyalin granules, which are filled with proteins that promote hydration and crosslinking of keratin.
At the transition between this layer and the stratum corneum, cells secrete lamellar bodies (containing lipids and proteins) into the extracellular space. This results in the formation of the hydrophobic lipid envelope responsible for the skin's barrier properties. Concomitantly, cells lose their nuclei and organelles causing the granular cells to become non-viable corneocytes in the stratum corneum.