Wrinkles - Ultraviolet Radiation, Sunlight, and Photoaging

Skin Care :: Wrinkles - Ultraviolet Radiation, Sunlight, and Photoaging

The role of the sun cannot be overestimated as the most important cause of prematurely aging skin (called photoaging) and skin cancers. Overall, exposure to ultraviolet (referred to as UVA or UVB) radiation emanating from sunlight accounts for about 90% of the symptoms of premature skin aging, and most of these effects occur by age 20:

Even small amounts of UV radiation trigger process leading to skin wrinkles.

Long-term repetitive and cumulative exposure to sunlight appears to be responsible for the vast majority of undesirable consequences of aging skin, including basal cell and squamous cell carcinomas.

Melanoma is more likely to be caused by intense exposure to sunlight in early life.
Initial Damaging Effects of Sunlight. Sunlight consists of ultraviolet (referred to as UVA or UVB) radiation, which penetrates the layers of the skin. Both UVA and UVB rays cause damage leading to wrinkles, lower immunity against infection, aging skin disorders, and cancer. They appear to damage cells in different ways, however.

UVB is the primary agent in sunburning and primarily affects the outer skin layers. UVB is most intense at midday when sunlight is brightest. Slightly over 70% of the yearly UVB dose is received during the summer and only 28% is received during the remainder of the year.

UVA penetrates more deeply and efficiently, however. UVA's intensity also tends to be less variable both during the day and throughout the year than UVB's. For example, only about half of the yearly UVA dose is received during the summer months and the balance is spread over the rest of the year. UVA is also not filtered through window glass (as is UVB).
Both UVA and UVB rays cause damage, including genetic injury, wrinkles, lower immunity against infection, aging skin disorders, and cancer, although the mechanisms are not yet fully clear.

Processes Leading to Wrinkles. Even small amounts of UV radiation trigger the process that can cause wrinkles, like:

Sunlight damages collagen fibers (the major structural protein in the skin) and causes accumulation of abnormal elastin (the protein that causes tissue to stretch).

In response to this sun-induced elastin accumulation, large amounts of enzymes called metalloproteinases are produced. (One study indicated that when people with light to moderate skin color are exposed to sunlight for just five to 15 minutes, metalloproteinases remain elevated for about a week.)

The normal function of these metalloproteinases is generally positive, to remodel the sun-injured tissue by manufacturing and reforming collagen. This is an imperfect process, however, and some of metalloproteinases produced by sunlight actually degrade collagen. The result is an uneven formation ( matrix) of disorganized collagen fibers called solar scars . Repetition of this imperfect skin rebuilding over and over again causes wrinkles.

An important event in this process is the over-production of oxidants, also called free radicals. These are unstable molecules that are normally produced by chemical processes in the body, a process called oxidation. With environmental assaults, however, such as from sunlight, they are produced in excessive amounts and damage the body's cells and even alter their genetic material. Oxidation may specifically contribute to wrinkling by activating the specific metalloproteinases that degrade connective tissue.

There is a possible upside to wrinkles and sun exposure. A 2001 study reported that people with more wrinkles were less likely to develop basal cell carcinomas, even among high-risk groups. Some experts suggest that people prone to wrinkles may respond to sun exposure with biologic mechanisms that protect against basal cell carcinoma. More research is needed confirm this.





(Skin Care :: Wrinkles - Ultraviolet Radiation, Sunlight, and Photoaging published at SpiritIndia on Wednesday, December 7, 2005)

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