Introduction

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 (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.