Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Keratinocytes
Introduction
The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells. The epidermis is divided into four or five layers (depending on the type of skin) based on keratinocyte morphology:
- stratum basale (at the junction with the dermis)
- stratum spinosum
- stratum granulosum
- stratum lucidum (only present in thick skin – i.e. palms of hand and soles of feet)
- stratum corneum
Keratinocytes originate in the basal layer from the division of keratinocyte stem cells. They are pushed up through the layers of the epidermis, undergoing gradual differentiation until they reach the stratum corneum where they form a layer of enucleated, flattened, highly keratinized cells called squamous cells. This layer forms an effective barrier to the entry of foreign matter and infectious agents into the body and minimises moisture loss.
Keratinocytes are shed and replaced continuously from the stratum corneum. The time of transit from basal layer to shedding is approximately one month. Although that approximate time frame can be accelerated in conditions of keratinocyte hyperproliferation, such as psoriasis.