Introduction:

As you age, your skin undergoes progressive changes:

• The cells divide more slowly, and the inner layer of skin (the dermis) starts to thin. Fat cells beneath the dermis begin to shrink. In addition, the ability of the skin to repair itself decreases with age, so wounds heal more slowly. The thinning skin becomes vulnerable to injuries and damage.
• The deeper layer of the skin, which provides scaffolding for the surface skin layers, loosens and unravels. Skin then loses its elasticity (ability to stretch). When pressed, it no longer springs back to its initial position. Instead, older skin sags and forms furrows.
• The sweat- and oil-secreting glands atrophy (waste away), leaving the skin without a protective layer of water and fat. The skin's ability to stay moisturized then decreases, and it becomes dry and scaly.
• Frown lines (those between the eyebrows) and crow's feet (lines that spread from the corners of the eyes) appear to develop because of permanent small muscle contractions. Habitual facial expressions also form characteristic lines.
• Gravity makes the situation worse, contributing to the formation of jowls and drooping eyelids. Eyebrows, surprisingly, move up as a person ages, possibly pulled up by forehead wrinkles.

Wrinkles can have a profound impact on self-esteem. The stigma attached to looking old is evidenced by the more than $12 billion Americans spend each year on cosmetics to hide the signs of aging. Our society places a premium on youthfulness, and age discrimination in the workplace, although illegal, has stalled many people's careers. Indeed, the emotional consequences of aging explain in large part why the cosmetics industry and plastic surgeons thrive.

Ultraviolet Radiation, Sunlight, and Photoaging

The sun is the most important cause of prematurely aging skin (a process called photoaging) and skin cancers. Overall, exposure to ultraviolet radiation from sunlight (radiation referred to as UVA or UVB) accounts for about 90% of the symptoms of premature skin aging. Most of these effects occur by age 20:

• Even small amounts of UV radiation trigger the processes leading to skin wrinkles.
• Long-term repetitive exposure to sunlight adds up, and likely is responsible for the vast majority of unwanted consequences of aging skin, including basal cell and squamous cell cancers.
• Intense exposure to sunlight in early life is an important cause of melanoma, a particularly aggressive type of skin cancer.

Initial Damaging Effects of Sunlight. Ultraviolet radiation 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 main cause of sunburns, and primarily affects the outer skin layers. UVB is most intense at midday when sunlight is brightest. People receive slightly over 70% of their yearly UVB dose during the summer. We receive only 28% during the remainder of the year. Window glass filters out UVB.
• UVA penetrates more deeply and efficiently. The intensity of UVA rays is less dependent on the time of day and season of the year than that of UVB rays. For example, you receive only about half of your yearly UVA dose during the summer months, with the balance spread over the rest of the year. Window glass does NOT filter out UVA.

Both UVA and UVB rays cause damage to the body, including genetic injury, wrinkles, aging skin disorders, and skin cancers. Exactly how they cause this damage is not yet fully understood.

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

• Sunlight damages collagen fibers (the major protein that gives structure to the skin). Sunlight also causes damage to elastin, a protein in the skin that normally maintains springiness and strength of tissue beneath the skin.
• In response to this sun-induced elastin accumulation, the body produces large amounts of enzymes called metalloproteinases. One study indicated that when people with light to moderate skin color are exposed to sunlight for just 5 - 15 minutes, the metalloproteinase levels in their body remain high for about a week.
• The normal function of these metalloproteinases is generally positive -- to remodel the sun-injured tissue by producing and repairing collagen. This is an imperfect process, however, and some of metalloproteinases produced by sunlight actually degrade (break down) collagen. The result is an uneven formation (matrix) of disorganized collagen fibers called solar scars. Repetition of this imperfect skin rebuilding 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. Environmental damage, however, causes an overproduction of oxidants. Excessive amounts of oxidants damage the body's cells and even alter their genetic material. Oxidation may contribute to wrinkling by activating the specific metalloproteinases that degrade connective tissue.

Other Factors Responsible for Wrinkles

In addition to sunlight, other factors may hasten the formation of wrinkles:

Cigarette Smoke. Smoking produces oxygen-free radicals, which accelerate wrinkles and aging skin disorders, and increase the risk for non-melanoma skin cancers. Studies also suggest that smoking and subsequent oxidation produce higher levels of metalloproteinases, the enzymes associated with wrinkles.

Air Pollution. Ozone, a common air pollutant, may be a particular problem for the skin. One study reported that it might deplete the amount of vitamin E in the skin. This vitamin is an important antioxidant.

Rapid Weight Loss. If weight loss occurs too rapidly, the volume of fat cells that cushion the face are also decreased before chemicals in the skin can react. This not only makes a person look gaunt, but can cause the skin to sag.