The epidermis slowly thins with age. Skin exposed to the sun ages most
quickly. Wrinkles are folds of skin that are more frequent on the face and hands
and become more numerous with age. Wrinkles are associated with loss of skin
elasticity and sagging of skin that increases the aging effect with the
development of deep fissures and folds.
Young skin is relatively tight, smooth and follows the contours of the
underlying tissue. Subcutaneous fat is the sculpting medium for body contours.
Skin that hugs the surface of the underlying fat looks young and healthy. With
aging, the skin and subcutaneous fat dissociate, sag and no longer look
attractive. Plastic surgery procedures remove redundant skin and fat, stretching
the remaining skin over the underlying structures to restore something of the
younger look. I seldom find the look of “face lifts’ appealing and the
inevitable loss of normal face movement can be quite distressing to an observer
of the altered face.
The development of wrinkles involves the deepest layers of skin and changes
in subcutaneous tissue. Surface treatment of wrinkles with lotions and creams
has minimal and transient effects. Contet-Audonneau described changes in aging
skin: “Fibers like candelabra extend perpendicularly from the lamina densa of
the dermoepidermal junction into the papillary dermis where they merge with a
horizontal network of elastin-containing fibers to form a continuous dermal
elastic fiber network… mainly composed of elastin and two glycoproteins,
fibrillin and microfibril-associated glycoprotein.
In photoaged skin, the elastic tissue overgrows… there is a decrease or
disappearance of oxytalan fibres. Severe depletion and reorganization of
fibrillin at the dermoepidermal junction of both mild and severely photoaged
skin indicates that the fibrillin microfibrillar network of the papillary dermis
is particularly susceptible to degradation by ultraviolet (UV) irradiation.”
Their study revealed that at the bottom of a wrinkle, collagens IV and VII
are decreased. In the dermis, they also found collagen atrophy and changes of
the elastic tissue, strongly modified in skin exposed to solar radiation. They
reported “voluminous masses of elastotic tissue” that forms pads on
each side of the wrinkle. Oxytalan fibres were decreased and were at the bottom
of the wrinkle, tending to disappear with age. Glycosaminoglycans and
chondroitin sulphates were decreased under the bottom of the wrinkle. They also
noted atrophy of the hypodermis with fibrous trabeculae thickening, more
pronounced under the wrinkle.
Collagen is critical to the mechanical framework of the skin and several
cellular processes. Collagen is a long-lived protein. Once damaged, it cannot be
repaired. Intermolecular cross-linking modifies collagen's biomechanical
properties, resulting in increased stiffness and vulnerability to mechanical
stimuli. The formation of glycation products on collagen side chains
alters the protein's charge and interferes with its active sites, thereby
distorting the protein's ability to interact properly with surrounding cells and
matrix proteins. The ability to convert L-arginine to nitric oxide, a critical
cofactor in the crosslinking of collagen fibers, is impaired. Glycated collagen
is highly resistant to degradation by matrix metalloproteinases (MMPs). This
further retards the process of collagen turnover and replacement with functional
proteins. Other cutaneous extracellular matrix proteins are affected by
glycation, including elastin and fibronectin.