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Causes of Photoaging
By peace | January 24, 2008
UV radiation readily penetrates the skin and damages molecules, especially DNA in the cell nuclei, which is important for cell function. This DNA damage is largely repaired, but some persistent abnormalities remain. These abnormalities may then gradually accumulate, leading slowly to skin photoaging or even eventually to skin cancer.
Approximately 5% of the UV radiation hitting the skin is reflected, the remainder passing into the tissue, being scattered and then passing out again, or else being absorbed by molecules in the various layers of the stratum corneum, epidermis and dermis. The short wavelengh UVB is largely removed in the stratum corneum and in the epidermis, particularly by DNA and melanin, whereas the longer UVA wavelengths are mostly transmitted to the dermis to be absorbed there predominantly by haemoglobin in the blood, or else reflected back up and out of the body.
Although UVB accounts for only a small proportion of the total solar UV radiation, it is nevertheless extremely important because these UVB wavelengths are the ones that are mainly responsible for causing sunburn, photoaging and cancer of the skin. This is because they are many times more effective than UVA in causing harmful changes to the genetic material of living cells, namely DNA. As a result, even though UVA comprises most of the total solar UV radiation throughout the year, it is generally responsible for only about 10-20% of the harmful effects of sun exposure. There is clear evidence that regularly exposing your skin to high dose of UVA from sunbeds causes damage similar to that resulting from exposure to sunlight, although sunbeds often emit a great deal of UVB as well. UVA also plays an important role in the development of a whole host of abnormal skin rashes caused by the sun.
Photoaging is the result of accumulated skin damage caused by UV radiation over many years. Just as for sunburn, it is UVB wavelengths that have the greatest effect. However, UVA exposure can also cause changes, although with a tendency to be deeper. These may affect you if you spend a lot of time on a sunbed or sunbathing using a sunscreen that blocks mostly UVB.
When the body is unable to fully repair damage to the DNA in the cells of the epidermis and the dermis, their structure deterioriates with changes that seem irreversible. In addition, the chemicals released during sunburn appear also to harm the dermis, especially causing damage to the network of collagen and elastic fibres that form the major support for the skin and help to keep it wrinkle-free, although this damage may recover over time. These fibres may also be directly damaged by UV exposure. All this means that your skin tends to become gradually drier, rougher and thicker, and thread veins and wrinkles also slowly develop.
Sunlight also causes changes to the melanocytes, which gradually stop functioning in a consistent fashion so your skin may develop a brown blotchiness; it may gradually yellow as well. Finally, your epidermis may become thinner and more fragile. All these changes together are the visible signs of skin photoageing. Other factors besides sunlight exposure may also contribute significantly to skin aging, and these include most particularly cigarette smoking.
Topics: Health, Man's health, Woman's Health |
January 25th, 2008 at 2:03 pm
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