Healthy young skin is smooth and firm, without blemishes, spots and wrinkles. It adopts to changes of temperature and humidity and reacts properly with the right care.
However, as the time passes, changes in the skin texture are unavoidable. It looses firmness and smoothness and the ageing process becomes obvious.
A healthy skin condition depands on hydration. Adequate moisturisation of stratum corneum is necessary. If neglected, the surface of the skin becomes dry and rough. Furthermore, permeability by harmful environmental agents become more likely.
The dermis (or lower layer of the skin) contains proteoglycans and glycosaminoglycans which retain water. In turn, water migrates to upper skin layer, the epidermis, and evaporates. The dermis is made of collagen and elastin which are responsible for the firmness and elasticity of the skin. As the skin ages it becomes dry, less elastic and appears tired.