It's a matter of common sense that putting your skin out in the sun is not good for its longevity. As it turns out, the way in which the sun damages your skin is more subtle than a blunt effect of direct radiation. Here's a look at one part of the way in which that happens:

Cutaneous aging occurs through 2 biologically distinct processes: intrinsic and extrinsic aging. The first is a naturally occurring process that results from slow tissue degeneration. In human dermis, intrinsic aging is characterized by 3 features: atrophy of the dermis due to loss of collagen, degeneration in the elastic fiber network, and loss of hydration.

In contrast to intrinsic aging, extrinsic aging is due to environmental factors. Since ultraviolet (UV) exposure is the principal cause of extrinsic aging, it is often referred to as photoaging. At the microscopic level, the distinguishing feature of photoaging is a massive accumulation of elastotic material in the upper and middle dermis, a process termed solar elastosis. Using recombinant DNA technology, it has become possible to demonstrate that UV radiation can activate the human elastin promoter. This provides a mechanism for enhanced elastin biosynthesis, which contributes to the clinical and morphologic changes observed in photoaged skin.

In other words, solar radiation changes the way skin is programmed to form and repair itself - for the worse. So much of aging is caused by malfunctions in the signal and control mechanisms of the body, processes necessary to the normal function of tissue run awry or amok, causing damage or - as in this case - changes in the structure of tissue that reduce its ability to function. Inflammation in the skin brought on by solar radiation is another example that contributes to aging of the dermis; necessary mechanisms subverted to set damaging processes in motion.