Ultraviolet (UV) radiation
The role of the sun cannot be overstated as the main cause of premature skin aging (called photoaging) and skin cancer. Overall, exposure to UV radiation from sunlight is responsible for about 90% of the symptoms of premature skin aging, and most of these effects occur around the age of 20. Even small amounts of UV radiation trigger the process that can cause wrinkles. Both UVA and UVB rays penetrate the layers of the skin and cause cell damage that leads to wrinkles, reduced immunity to infections, aging skin conditions and even cancer.
Sunlight damages collagen fibers (the main structural protein in the skin) and causes abnormal elastin (the protein that causes tissue to stretch) to build up. In response to this sun-induced accumulation of elastin, large amounts of enzymes called metalloproteinases are produced. The normal function of these metalloproteinases is generally positive, which is to repair the sun-damaged tissue by creating and reforming collagen. However, this is an imperfect process, as sunlight-induced metalloproteinases also break down collagen. The result is an uneven formation of disorganized collagen fibers, which are called sun scars.
Repetition of this imperfect skin reconstruction causes wrinkles over and over again. An important factor in this process is the overproduction of oxidants, also known as free radicals. Sunlight can produce excessive amounts of free radicals and damage the body's cells and even alter their genetic material. Oxidation can specifically contribute to wrinkles by activating the specific metalloproteinases that break down connective tissue. There is also a positive side to wrinkles and sun exposure. A recent study reported that people with more wrinkles were less likely to develop basal cell carcinomas, suggesting that people prone to wrinkles may respond to UV rays with mechanisms that protect against basal cell carcinomas.
Cigarette smoking produces oxygen-free radicals, which are known to accelerate wrinkles and skin aging and increase the risk of non-melanoma skin cancer. Studies also indicate that smoking produces higher levels of collagen-degrading metalloproteinases. Ozone, a common air pollutant, can be a particular problem for the skin. One study has shown that it can reduce the amount of vitamin E in the skin; this vitamin is an important antioxidant. If the weight loss is too fast, the volume of the fat cells that protect the face also decreases before the chemicals in the skin can react. This not only makes a person look thin, but can also cause the skin to slacken and develop deep wrinkles.