What is the life cycle of the keratinocyte?

The functional and morphology of keratinocytes significantly changes throughout their life cycle, which under physiological conditions lasts approximately 30-50 days in humans. However, in the case of increased rates of proliferation to injury, neoplasia, or inflammation, the timespan of this process may vary. Keratinocytes first proliferate in the basal layer of the epidermis and begin to differentiate as they reach the surface. They migrate upwards into the stratum spinosum as newer cells being generated below push them. As the cells move upwards, they become flattened and eventually cease mitosis. They then initiate apoptosis as they reach the stratum granulosum. The dead keratinocytes (corneocytes) reach the stratum corneum and peel off.