We begin to age the moment we are born, and throughout our lives the effects of aging are evident in our bodies. Up to about age 20, the most visually prominent effects of aging are in growth and development. Starting in our 20s, the effects of aging begin to be visible in the skin.

Genetically programmed chronologic aging causes biochemical changes in collagen and elastin, the connective tissues that give skin its firmness and elasticity. The genetic program for each person is different, so the loss of skin firmness and elasticity occurs at different rates and different times in one individual as compared with another.

As skin becomes less elastic, it also becomes drier. Underlying fat padding begins to disappear. With loss of underlying support by fat padding and connective tissues, the skin begins to sag. It looks less supple, and wrinkles form. The skin may be itchy with increased dryness. A cut may heal more slowly.

Simultaneously with genetically programmed aging, the process of photoaging may take place. Photoaging is the effect of chronic and excessive sun exposure on the skin. Cigarette smoking also contributes to aging effects by the biochemical changes it brings about in skin tissues.

Photoaging interacts with chronologic aging and may appear to hasten the process of chronologic aging. In fact, photoaging may be responsible for the majority of age-associated changes in the skin's appearance: mottled pigmentation, surface roughness, fine wrinkles that disappear when stretched, "age" or "liver" spots (lentigines) on the hands, and dilated blood vessels. Chronic sun exposure is a major risk factor for skin cancers — basal cell carcinoma, squamous cell carcinoma and melanoma.

The effects of photoaging accumulate over years of chronic sun exposure. At first, the effects may be invisible to the casual glance, even while they are on the increase. Photos taken with ultraviolet light will dramatically reveal the accumulative effects of chronic sun exposure. In the following series of photos, the accumulative effects of chronic sun exposure are clearly seen. In each set of photos, the first two pictures were taken in ordinary light, the third picture in ultraviolet light. As skin ages and accumulates sun damage, a number of lesions (sores or spots on the skin) become more common. These include:

"Age" and "liver" spots (lentigines) — flat, brown areas with rounded edges usually found on the face, hands, back and feet. They are age-related and photoaging-related, and have nothing to do with the liver. While they are unsightly, they are not dangerous. However, a large, flat, dark area with irregular borders should be examined by a dermatologist to make sure it is not melanoma.