The stratum granulosum functions as the waterproofing layer of the skin that prevents fluid loss, according to the Loyola University Medical Education Network. Keratin accumulates in this layer by a process that forms a thicker layer of skin cells to protect less dense cells underneath. Lipids and keratin organize as flat skin cells without their nuclei, according to Dr. Heather Brannon for About.com.
University of Leeds notes that the stratum granulosum consists of three to five layers of cells stacked on top of each other. These granules contain lipids, or fats, that serve as the skin's water sealant. When keratinized cells lose their nuclei and other cellular organelles, granules move toward the outermost layers of skin. The stratum granulosum is the third layer of the epidermis that lies below the stratum corneum and stratum lucidum.
The stratum granulosum marks a transition from living skin cells to completely dead skin cells of the outermost layer of the epidermis. Just below the granule layer lies the prickle cell layer of skin cells. University of Leeds explains these cells turn into granules as they get pushed upwards and flatten. Right above the granules lies a thin, transparent layer called the stratum lucidum in thick skin. The stratum lucidum may not be present in thin skin. The stratum corneum serves as the outermost layer of skin comprised of dead cells. The entire process of skin cells moving through four major layers takes between two to four weeks.