The human skin is a dynamic and complex organ with a unique structure. It consists of different cell types and layers with different functionalities.
Primarily made up of three layers, the upper layer is the epidermis, the layer below is the dermis, and the third and deepest layer is the subcutaneous tissue.
The outermost layer, the epidermis, plays a significant role in protection, regulating water loss from the body (Transepidermal Water Loss, TEWL) and reducing the impact of environmental damage and pathogens. It consists of four sublayers – stratum corneum, stratum granulosum, stratum spinosum and stratum basale.
On thick skin areas such as palms and soles of the feet; the epidermis consists of an extra layer, stratum lucidum.
The epidermis also consists of four major cell types – keratinocytes, melanocytes, langerhans cells and merkel cells.
The border between the epidermis and dermis, the epidermal–dermal junction, consists of an aggregation of proteins and structures known as the basement membrane.
Below the basement membrane, is the dermis, which provides structural support, as well as nutrition and circulation in the skin.
The dermis comprises dendritic cells, macrophages and mast cells, primarily from fibroblasts; which produce an interconnected extracellular matrix of collagenous and elastic fibers. The dermis also contains blood and lymph vessels, nerves, hair follicles and sweat glands.
The deeper subcutaneous tissue/hypodermis is made of fat and connective tissue.
Ageing affects all skin layers, their structure and function.
Aged/mature epidermis has less capacity for barrier function and restoration following any sort of injury. There is also a lipid processing decline, as well as a decrease in the epidermal levels of a glycoprotein that helps maintain the production of local hyaluronic acid resulting in dryness.
With age, cell replication in the basal layer declines. This results in the epidermis becoming thinner, and the contact surface area between the dermis and epidermis diminishing, resulting in a smaller exchange surface area for nutrition supply to the epidermis and a further weakened ability of basal cells replicating.
Besides the epidermis, both the epidermal–dermal junction and dermis also become thinner. The flattening of the epidermal–dermal junction leads to fewer cells, less nutrition and less oxygen, resulting in wrinkle formation and loss of elasticity.
As we mature, it is important to adapt our skincare routines to address intrinsic, as well as extrinsic skin ageing.