Basal cell carcinoma accounts for more than 90 percent of all skin cancers in the United States. It is a slow-growing cancer that seldom spreads to other parts of the body.
Basal cell cancer, pictured here, usually occurs on areas of a person's skin that have been exposed to the sun. Often, it appears as a small, raised bump that has a smooth, pearly appearance. However, it can also look like a scar and seem firm to the touch.
Squamous cell cancer usually occurs on parts of a person's body that have been exposed to the sun. Often, it appears on the top of the nose, forehead, lower lip, and back of the hands. It also may appear on skin that has been severely sunburned, been exposed to carcinogenic chemicals, or had X-ray therapy.
Squamous cell cancer, shown here next to a person's left eye, often appears as a firm red bump; sometimes it may feel scaly or bleed or develop a crust. Squamous cell cancer rarely spreads, but it does so more often than basal cell cancer. Squamous cell cancer may spread to nearby lymph nodes.
Melanoma is the most serious cancer of the skin. In some parts of the word, especially among Western countries, the number of people who develop melanoma is increasing faster than the number for any other cancer. In the United States, the incidence of melanoma has more than doubled in the past 20 years. One explanation for this trend is increased recreational exposure to the sun.
The most important ways to protect one's skin from UV-related damage are to avoid exposure to UV radiation, especially during peak hours, and to wear protective clothing and sunscreen when outside.
Avoiding exposure is the best protection from UV-related skin damage. Behaviors that can help include scheduling outdoor activities during the early morning or late afternoon and evening, when UV radiation is lower; seeking shade when outdoors during hours of peak exposure; and not using tanning salons.
Wearing protective clothing also can help reduce exposure. For example, wide-brimmed hats that shade the face and darkly colored, tightly knit, long-sleeved shirts and long pants offer significant protection from UV exposure.
A sunscreen is a chemical that absorbs UV radiation. Sunscreens are rated by their SPF, or sun protection factor. An SPF is measured by determining how long a particular person's skin takes to burn with and without the sunscreen. If it takes 10 times longer to burn with the sunscreen than without, then that product has an SPF of 10. Experts recommend that people use a broad-spectrum sunscreen (one that protects against both UVA and UVB) with an SPF of 15 or more.
Sunscreens can extend the amount of time a person can spend in the sun without burning. However, because even high SPF sunscreens allow some UV radiation to reach the skin, they are not a substitute for avoiding the sun during peak hours of UV exposure and wearing protective clothing.
According to a recent survey by the American Academy of Dermatology, only 4 in 10 Americans believe that it is important to protect themselves from the harmful effects of the sun. This finding may explain why only 15 percent of the people questioned say they wear a sunscreen whenever they go outside and more than 25 percent say they usually don't wear sunscreen at all.
Other survey findings include the following:
Slightly over half (52 percent) of the people who responded to the survey say they wear sunscreen in the summer; less than 15 percent responded that they wear it year-round.
Most people (84 percent) believe they need to wear sunscreen only if they're going to be outside for a long time.
Approximately 35 percent of the people responding to the survey believe that only those who burn easily need to wear a sunscreen with an SPF of 15 or higher.
Seventy-six percent of the people responding reported that they wear sunglasses when outside in the sun, 43 percent reported that they wear protective clothing, and only 36 percent reported that they wear a wide-brimmed hat.
The sun is critical for our existence on earth. It provides the energy required for photosynthesis, keeps us warm, and provides the light we see by.
The sun's ultraviolet (UV) radiation, however, is very dangerous to us. It causes sunburns as well as tans, skin cancer, and most of the age-related changes we see in our skin as we age (such as deep lines and sagging skin).
Scientists recognize three types of UV radiation: UVA, UVB, and UVC. Almost all UVC radiation is filtered out by the atmosphere, so almost none reaches the earth's surface. UVA and UVB radiation, however, both reach the earth's surface in significant amounts.
UVB is more damaging to skin than UVA. However, as much as 100 times more UVA reaches the earth's surface as UVB, so UVA is still dangerous. UVA causes pigment in the skin to darken but does not contribute significantly to common sunburn. However, it does contribute to skin aging and may contribute to the development of skin cancer.
Both tanning and sunburn are primarily caused by overexposure to UVB radiation. During a sunburn, the skin turns red, swells, and in severe cases, blisters. A sunburn continues to develop for as many as 12 to 24 hours after the exposure.
Exposure to UV radiation also can damage immune system cells located in the skin. These cells help ward off bacteria and also may be involved in recognizing and eliminating cancerous cells. Thus, a few minutes of unprotected UV exposure is dangerous in two ways: it causes the damage that can lead to skin cancer and cripples one of our normal defenses against cancer.
Another harmful effect of UV radiation occurs deep in the lower levels of the skin, where bundles of a protein called collagen provide strength and texture to our skin. In young, undamaged skin, collagen fibers are arranged in an orderly fashion. As the fibers accumulate more sun damage, they lose their orderly arrangement. Collagen that is damaged in this way is no longer strong and supple, and this results in the limp skin that we associate with aging. In fact, most of the changes that we see as our skin ages are actually due to sun exposure and could be avoided with proper protection.
The amount of UVB radiation in a given location is determined by several factors. One important factor is latitude, or distance from the equator. The amount of UVB received annually in Hawaii (at about 19 degrees north of the equator) is approximately 10 times the amount received in Alaska (at about 72 degrees north).
UVB radiation also increases with increasing altitude, or distance above the surface of the earth. For every 1,000 feet of altitude, the UV radiation increases by about 4 percent. This means that approximately 20 percent more UV radiation reaches the earth's surface in Denver, Colorado, than in a city that is at a similar latitude but at sea level.
Time of day and year and the amount of sky cover also affect UV radiation. More UVB reaches the earth's surface when the sun is most intense, typically on sunny summer days between 10:00 a.m. and 2:00 p.m. However, UVB exposure still can be significant in fall, winter, and spring. Because as much as 80 percent of the sun's rays can penetrate light clouds, mist, and fog, it is possible to experience dangerous UV exposure on nonsunny days.
Many surfaces, such as sand, snow, and cement, reflect most of the UV light that hits them. This means that it is possible to be in the shade and still experience dangerous UV exposure.
Some experts fear that ozone depletion in the upper atmosphere, which is linked to the amount of UVB radiation that reaches the earth, may increase the incidence of skin cancer. As evidence for this, some experts point to the Australian example: Australia suffered an average 2 percent ozone loss across the period from 1980 to 1988, and an estimated annual average UVB increase of 3 to 11 percent across the same period. Australian experts predict that for every 1 percent of UV radiation increase, a corresponding 2,500 new cases of skin cancer will occur each year after a lifetime of exposure to the increased radiation.
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