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September 2003

What You Don’t Know About the Dangers of Sun Damaged Skin

By Kimberly Haas

As we age, we start to see the effects of sun exposure that occurred years ago. Aging skin reacts differently to the sun and becomes increasingly susceptible to sunburns and additional damage. One reason is a decrease in the release of melanin, a compound that protects the skin against UV (ultraviolet) radiation.1

Scientists have identified surprising new factors that make aging skin more vulnerable to sun exposure than young skin. In this article, we examine the reasons for these age-related skin changes, as well as ways to protect it from further damage and the development of cancer.

The incidence of skin cancer has increased dramatically over the recent decades.2 The ozone layer problem is partly to blame, as the depletion of this important layer of the earth’s atmosphere allows more ultraviolet radiation to reach us. We are also to blame.

Until the end of World War II, having a suntan was looked down upon by the upper classes as vulgar and people went to great lengths to protect themselves from the sun. After the war, however, tanned skin became thought of as healthy and fashionable, an image that still persists in some circles today.3 The longevity and prosperity that modern Americans enjoy have also contributed to skin cancer rates. In fact, the sharp rise in the number of people with melanoma (malignant skin cancer) has been attributed to the fact that many Americans now have enough disposable income to travel to warm locations during the winter—getting intense sun exposure at a time they never had before.2 Also, people are increasing their exposure at home because they have more time for recreational activities such as boating or skiing.3

As a result, the incidence of melanoma has risen faster than any other type of cancer in developing countries over the past 50 years.4 Mortality from the disease is rising as well.4 According to the American Cancer Society, 54,200 Americans will be diagnosed with melanoma this year alone and 7,600 will die from the disease. Also this year, more than one million people will be diagnosed with one of the less dangerous types of skin cancer.

Although most sun damage occurs when we are young, the skin’s decreasing ability to protect itself against the sun as we age means that further damage can occur. Even people who’ve spent a lifetime in the sun can—and should—still take steps to protect their skin.

How the skin reacts to sunlight
Ultraviolet (UV) radiation is responsible for the changes that occur when skin is exposed to sunlight. Short-term changes include sunburn and tanned skin, while long-term changes include wrinkling, moles and skin cancers. UV light has many components, but only two main types reach the earth’s surface: UVA and UVB. The two types of light operate on different wavelengths and affect the skin in different ways. UVB, which has a shorter wavelength than UVA, affects only the upper layers of skin. It is responsible for most sunburns and the formation of initial DNA changes that can lead to skin cancer.2 However, the longer-wavelength UVA makes up a much greater portion of sunlight, penetrates into the lower layers of the skin and causes tanning. Newer research has found that UVA can also damage DNA and is thought to lower the immune response of the skin, making it less able to fend off early tumors.2

When sunlight hits the skin, cells called melanocytes (located between the outer and middle layers of the skin) begin to take action. Melanocytes continually release small amounts of the brown-black pigment called melanin into the skin; exposure to sunlight signals the melanocytes to produce more melanin. Melanin determines our normal skin color and attempts to protect our skin from severe sun damage.

Melanin is the body’s defense system against acute burns, says Sandra Read, M.D., a dermatologist in private practice in Washington, D.C. and at Georgetown University. “Pigment keeps skin tanned, but burned,” she says. “But this is an important distinction: you’re not getting an acute burn, but you’re still accumulating sun damage.”

As we age, our melanocytes begin to function less effectively. The density of active melanocytes in the skin is reduced by 10% to 20% every 10 years starting in our late 30s and 40s. (Melanocytes are also responsible for hair color, so their loss explains why 50% of people are gray by age 50.) Skin with a reduced number of melanocytes is less able to respond to sun exposure, so UV radiation is better able to damage the skin. An Australian study of 97 men age 50 or older found that melanocyte density decreases with advancing age. The researchers also found that the density of remaining melanocytes varies by site on the body. The highest densities were seen on the back and shoulders, followed by the arms and legs, then the lower back. This uneven distribution of melanocytes may help explain why melanoma—cancer of the melanocytes—is more common in these areas.5

The loss of functioning melanocytes—and the impaired actions of the remaining ones—causes a wide range of skin changes, from merely cosmetic to life-threatening.

Long-term effects of the sun
In addition to photoaging (cosmetic skin changes caused by exposure to the sun, rather than by the passage of time), other non-serious consequences of sun exposure can occur, such as liver spots, actinic keratoses and moles.

Liver spots, which have nothing to do with the liver, should really be called age spots or photoaging spots (although the technical term is lentigines or lentigos). They are extremely common and occur when melanocytes cluster together under the skin and appear as light to dark brown—or nearly black—flat patches of pigment on the skin. Age spots usually have rounded edges, which make them look like large or exaggerated freckles. They appear mostly on the sun-exposed skin of people 40 and older. Age spots are not considered to be cancerous or precancerous. However, any age spot with uneven (rather than rounded) edges may really be a melanoma lesion and should be examined by a doctor.

A mole occurs when a group of melanocytes and surrounding tissue cluster together to form a growth on the skin. Moles, also called nevi (the singular form is nevus) vary in size and can be pink, tan, brown or flesh-colored. They can be either flat or raised, are usually round or oval and rough or smooth. Moles occur most often on the torso, but also can appear on the face, arms and legs; less common locations include on the scalp, under the nails, in the armpits or around the genitals.

Moles are very common—the average person has between 10 and 40 moles. Some are present since birth, most appear by age 20 and new moles can still appear up to age 40. Moles can change in appearance over time and some may even disappear. Experts do not think moles serve any purpose, but some can turn into melanomas. About one in every 10 people has at least one mole that appears abnormal, called a dysplastic nevus. Although the risk is still low, dysplastic nevi are more likely than normal nevi to become skin cancer.

It is important to know the location and appearance of your moles.6 Any change in their appearance should be reported to your doctor, who may remove the mole or take a tissue sample (biopsy) to determine whether it is skin cancer.

Actinic keratoses, also called solar keratoses, usually begin to develop in middle age as a result of chronic sun exposure. However, they may also develop in younger people with very fair complexions. Between 11% and 26% of the population is estimated to have at least one actinic keratosis lesion. Actinic keratoses are dry, scaly lesions that can be either flat or raised, like a bump on the skin; they can be reddish-brown, yellowish-black or the color of the skin. Some actinic keratoses, especially those that are skin-colored, can be more easily felt than seen.

Although most people consider them unattractive, actinic keratoses themselves are considered harmless. However, approximately 10% of these untreated lesions develop into squamous cell carcinoma, a nonmalignant form of skin cancer. Actinic keratoses can be frozen off (cryotherapy), burned off (electrical cautery) or removed surgically. Certain topical medications can also cause the lesion to peel off.

Skin cancers
The more serious consequences of sun exposure include basal cell carcinoma, squamous cell carcinoma and malignant melanoma.