Keratinocytes are only considered dead cells in the outermost layer of the epidermis, the stratum corneum. As they migrate upwards through the epidermal layers, they move farther away from the capillaries supplying vital nutrients. This nutrient deprivation leads to their death by the time they reach the skin's surface.
The Journey of a Keratinocyte: From Life to Death
Keratinocytes are the primary cells of the epidermis, making up approximately 90% of its composition. [^1] They are produced in the basal layer, the deepest layer of the epidermis. As new keratinocytes are formed, older ones are pushed upwards. During this ascent, they undergo a process called keratinization. This involves the production of keratin, a tough, fibrous protein that gives skin its protective barrier. [^2][^7] As keratinization progresses, the keratinocytes lose their nucleus and other organelles, effectively dying. [^3][^5][^6][^8] These dead, keratin-filled cells, now called corneocytes, form the stratum corneum. [^4][^9] The stratum corneum acts as a crucial protective barrier against environmental hazards. [^9]
- Basal Layer (Stratum Basale): Living, actively dividing keratinocytes.
- Upper Epidermal Layers (Stratum Spinosum, Stratum Granulosum): Keratinocytes are still alive but begin the keratinization process.
- Stratum Corneum: Keratinocytes are dead, filled with keratin, and form a protective, waterproof layer.
The death of keratinocytes in the stratum corneum is a natural and essential part of skin's protective function. These dead cells are continuously shed and replaced by new ones from below, maintaining the skin's integrity. [^5] The process is not simply necrosis (unplanned cell death) but a regulated process called cornification. [^10] The controlled death of keratinocytes helps prevent harmful substances from penetrating the skin and aids in the maintenance of a healthy skin barrier. [^3]
[^1]: Keratinocyte - Wikipedia
[^2]: Layers of the Skin - SEER Training
[^3]: A unique mode of keratinocyte death requires intracellular ...
[^4]: Anatomy, Skin (Integument), Epidermis - StatPearls - NCBI Bookshelf
[^5]: 5.1 Layers of the Skin – Anatomy & Physiology
[^6]: What is Acne? Definition & Types | NIAMS
[^7]: How to Train Your T Cell(s): The Hidden World
[^8]: Epidermis (Outer Layer of Skin): Layers, Function, Structure
[^9]: Death penalty for keratinocytes: apoptosis versus cornification | Cell ...
[^10]: Death penalty for keratinocytes: apoptosis versus cornification | Cell ...
