There are many factors that can influence cellular regeneration and epidermal growth. For instance, the skin's natural response to excessive sunlight is to become thicker. This can result in slower shedding and a dry, rough skin. Acne sufferers, for example, may retain their skin cells, causing further congestion and thickening of the stratum corneum (top skin layer).
Other factors, such as age, genetics, hormone balance, lack of minerals, and inadequate diet, all influence epidermal cellular turnover and the production of new, healthy cells.