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Dermal disorders
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Crows feets, Wrinkles, starting form the edge of the eyes.
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| Lentigo actinic |
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The skin passes through two major stages in the life of an individual. From birth up to the age of 20 the skin matures. After 20 the skin embarks on a long period of ageing.
At birth, the skin of the newborn, though it seems like an adult one, does have differences. The horny layer is thin, the sebaceous gland secretions cease after the first six months of life, whereas they were very active during intra-uterine life. Because there is no lipidic film, the skin is very suseptible to dehydration. At puberty, the sebaceous glands regain activity triggered by the production of the sex hormones.
From the age of twenty, the skin begins to be subject to the consequences of chronological ageing, causing its appearance to slowly and imperceptibly change.
Ageing over time is the result of a slow, gradual, genetically programmed process, and the aggressions, our skin is subjet to, daily.
The first signs of ageing are seen in the skin of the face. All those funny faces, smiles, twitchings, screwing up the eyes, pursing of the lips finally leave their mark on the skin. These are the origin of the tiny expression lines causes by tension in the facial muscles which draw on the deepest parts of the dermis and over time form deep wrinkles.
The first areas affected are the eye corners where "crows' feet" develop. They start at the eye external angle, as fine cracks then spread out in a fan, deepening to form a network of wrinkles. This process evolves over years before becoming visible. A speeded-up simulation shows this phenomenon clearly.
crow feet formation: low bandwidth
crow feet formation: high bandwidth
The wrinkles spread little by little over the whole face (the forehead, lips, from the base of the nose to the corners of the lips), the neck, then to all the other parts of the body.
The loss of elasticity of the dermis is not only seen in the appearance of wrinkles. Looseness of the skin is a phenomenon which is also visible on the arms, where the skin frequently becomes distended. The same phenomenon can be seen on the neck.
wrinkles formation around the neck: low bandwidth
wrinkles formation around the neck: high bandwidth
Deep changes occur in the dermis. These changes are all the greater as renewal of the proteins of the dermis is very slow. Proteins with a long half-life, collagen and elastin, are subject to modification on contact with glucose. Glucose reacts spontaneously (without the intervention of enzymes
) to produce "AGE products" (advanced glycation end products). Glycation modifies the properties of these proteins. They are more resistant to proteolysis, preventing their renewal. In addition, the AGE products induce the cross-linking of collagen fibres, disorganising their network and making them more rigid and less soluble. The fibroblast population diminishes by half between the ages of 20 and 80. The fibroblasts, which have ensured a balance between the synthesis, maturation of collagen and elastin fibres, and their destruction by collagenases and elastases, tip this equilibrium towards the breakdown of collagen or elastin fibres This results in a loss of elasticity and tone in the dermis, flaccidity, which is no longer able to counteract the effects of the contraction of the underlying muscles, resulting in the appearance of wrinkles.
The vascularisation of the dermis is reduced, the skin changes colour: gradually it loses its pink tint and becomes pale, even yellowish, especially in the neck and nape area. Less nutrients are therefore being supplied.
The dermo-epidermal junction is flatter since the papillae are less numerous. The surface for exchange with the epidermis is reduced.
The glycosaminoglycans (GAG) of the dermis decrease. These sugar based molecules trap water in the dermis. Their diminution causes a reduction in the dermal and epidermal hydration.
Of the skin three compartments, dermis is the most deeply altered during the process of ageing, but the other components are not spared modification.
Epidermal thickness is reduced, whist, at the same time, the thickness of the horny layer increases. Keratinocyte renewal is slower, but their terminal differentiation is also slowed down. Epidermis hydration is decreased. Langerhans cells are less active, so immunity is reduced, meaning greater sensitivity to infections. A lot of elderly people have pigmented spots on their hands. The melanocytes are less active, but the melanosomes are larger.
They accumulate in certain areas thus forming pigmented spots which become permanent.
The hypodermis is thinner , the skin collapses.
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Deep wrinkles characteristic of sun exposed skin (Ex).
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Reorganisation of elastin fibres network (bleu) after UV irradiation.
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The effects of ageing produced by ultraviolet light and in particular by UVA rays amplify and speed up those due to chronological ageing. From this point of view it is not incorrect to say that UVA rays speed up time. In zones normally protected from sunlight, by clothes, the wrinkles are a lot finer and not as deep as in exposed areas The "rhomboid" area of an old sailors' neck and the face of are typical examples, with deep wrinkles, roughness, loose skin, pigmentation, from the effects of UVA irradiation on fibroblasts and elastic fibres. A few weeks after sun exposure, the tan fades, but the deeprooted harmful effects are retained. They accumulate from one year to the next and produce deep wrinkles and spots of pigmentation. This accumulation is due to the excessively slow dermal renewal. In the dermis the most striking modification being the accumulation of bundles of elastin fibres.
Elastin fibres are normally positioned perpendicular to the skin surface, but these bundles, after repeated exposure to UVAs, become parallel to it. It is therefore particularly important to be protected from the harmful effects of UVA irradiation. The daily use of skin care containing suscreens (UVA filters) is primordial to fight against UVA induced ageing. In summer the use of sunscreen products that offer protection from both UVB and UVA rays is also essential.
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Coloured lines landmark of strech marks
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Stretch marks are a disorder mainly affecting elastic tissues. Dermis loses its ability to resist extension and as a consequence becomes more exposed to collagen fibre rupture. Stretch marks are linear cutaneous depressions parallel to cutaneous stress lines, characterised mainly by a reduction in the density of the elastin fibre network and a thinner epidermis. The main sites for stretch marks are the sides of the thighs, the lumbar-sacral region, the abdomen around the navel and the breasts. They occur especially in tissue sensitive to hormone level disruption (post-pregnancy), nutritional deficiency (diets) or in a period of growth.
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