Continuous Skin Cell Mitosis: Renewal, Repair, and Adaptation

Epidermal keratinocytes undergo constant mitosis to maintain the skin barrier. Key drivers:

1. Cell turnover: Surface cells shed (desquamation); basal layer replaces them (~28-day cycle).
2. Growth: Skin expands with body growth.
3. Wound healing: Local proliferation surge closes defects.
4. Barrier maintenance: New cells replenish lipids, proteins (filaggrin, keratin), antimicrobial peptides.
5. Environmental adaptation: UV, humidity, temperature, irritants modulate proliferation/differentiation.
6. Appendage formation: Hair follicles, sebaceous/sweat glands require ongoing cell production.

Regulated by growth factors (EGF, KGF), cytokines, Wnt/β-catenin, Notch pathways. Dysregulation → psoriasis (hyperproliferation), cancer, chronic wounds.