What happens to skin as it ages is a model of how time reshapes human tissue. Skin ageing used to be seen as inevitable. Increasingly, it is seen as a process that can be effectively corrected with the right action.
Keratinocytes in the epidermis (the top layer of skin) and fibroblasts in the thick, biologically active dermis hold in their nuclei the blueprints for making healthy skin. Ageing happens when these blueprints are damaged and stop being read correctly.