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Issue
39 — July 2005 |
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Aging
of the human skin |
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The formation of lines and wrinkles in light-exposed areas throughout the
body, such as on the face, throat, décolleté and hands is
a well-known sign of skin aging. Lines and wrinkles are influenced by both
intrinsic and extrinsic factors. The numerous intrinsic factors are age,
gender, genetic disposition and race. In exposed and unprotected zones of
the body such as on the skin of the hands and the face, extrinsic factors
such as UV light, weather and climatic influences, nutrition, tobacco and
alcohol abuse, effect the formation of lines and wrinkles.
With increasing age, the physiology and appearance of the human skin will
change. Alterations in structure, loss in tightness, smoothness and a decrease
in the skin's functional capacity are phenomena which may be attributed
to the aging mechanism. An increase in dryness and thus roughness as well
as a loss in elasticity and even pigmentation are also a sign of increasing
skin aging. Wrinkles on flaccid skin develop with growing age. There is
a decline in the subcutaneous fatty tissue. Today, relatively little is
known about the exact biochemical processes of skin aging. Mature skin is
characterized by a decreasing barrier function, slower metabolic activities
in all cells, a strong loss in humidity as well as a decrease in activity
of the sebaceous and sweat glands.
Primarily, changes in the skin's appearance are a result of a general aging
process of the connective tissue of the subcutis. This leads to an atrophy
of the epidermis which adjoins the papillary layer and to an irregular decrease
in the elasticity of the elastic nets which are structures accompanying
the collagen fibres in the connective tissue. As a result of the changed
amount and chemical composition of the basic substance of the connective
tissue, a loss of liquids is the result, which consequently leads to a decrease
in glycosaminoglycans, the basic structures of the connective and supporting
tissues. As a consequence, the youthful turgor, i.e. the skin's tension,
is lost. Melanocytes disintegrate or lose close contact to epidermal cells
and finally lead to a spotted pigmentation of the skin.
Our illustration shows a schematic cross-section through the layers of the
skin. The epidermis, also known as corium or horny layer and dermis are
represented here. In the stratum corneum, the outer visible part of the
epidermis, horny cells and horny substances are baked together and form
plates. These plates are sloughed off as horny flakes.
In the enlarged area of our illustration the dense network of collagen fibres
is represented. This is a typical feature of the dermis. This fibre net
is made up of collagen, a protein and main component of intercellular supporting
substances, provides the skin with tensile strength and a reversible formability.
The dermis which holds blood and lymph vessels, the nervous network, connective
tissue cells and cells of defense, is rich in glycosaminoglycans which are
in charge of retaining water in the cells. Bundles of collagen fibres which
are responsible for the building of tension within the connective tissue
and show a disorderly alignment.
Younger skin shows a more complex network, a crossed and spiraled order
of collagen fibres which - as aging progresses constantly loses its density,
firmness and regular alignment.
Both epidermis which is located over the dermis, and the basal membrane
which connects these two skin layers, are effected by aging mechanisms.
In the dermis, changes in the composition of matrix proteins are primarily
to be attributed to a loss in the skin's firmness and elasticity.
The aging process of the skin is a complex mechanism which is of particular
interest for the cosmetic industry. Wrinkles and fine lines, especially
on facial skin, are also a major topic in dermocosmetics. Effective products
which may slow or delay skin aging or which prevent premature aging thus
should have an effect on all relevant skin layers. Skin damage which is
caused by sunlight may be counteracted by a number of antioxidants which
fight free radicals and have a protective effect on the skin. The use of
moisture-retaining substances is highly recommended in the treatment and
care of aged skin.
Source: H. Leonhardt, Histologie, Zytologie und Mikroanatomie des Menschen, Volume
3, 8th Edition, Thieme 1990.
