Ultraviolet Radiation

Choose Your Cover - Cancer Prevention and Control (CDC)

SunWise Program for Educators (EPA)UV Index Forecast for Your Location (EPA)

Problems Caused by Ultraviolet Radiation and Overexposure

Skin cancers and cataracts are increasing throughout the world. Many scientists believe that these and other serious health problems are now due to decreasing levels of ozone in the upper atmosphere and increasing levels of ultraviolet radiation reaching the Earth' surface, as well as the growth in outdoor work and recreation activities.

Skin cancer, which is mainly caused by overexposure to the sun, is at epidemic proportions in the United States—with one in six Americans now expected to develop this disease in their lifetime. Furthermore, cataracts, which are responsible for a large percentage of blindness in the world, have been attributed to chronic exposure to the sun's rays.

In the early 1990's, the American Academy of Dermatology announced that the incidence of malignant melanoma in the United States increased 321% between 1950 and 1989, and that since 1973, melanoma has been increasing about 4% per year. Based on this same data, the Academy predicted that over one million new cases of skin cancer would be diagnosed each year in the U.S. At the same time, the American Academy of Ophthalmology and other eye care groups predict that the incidence of cataracts in the U.S. will increase to 1.6 million cases annually by the year 2000.

Types of Ultraviolet Radiation:

While the sun's rays are essential for both plant and animal life, the very short ultraviolet (UV) wave-lengths can actually damage living cells. They contain enough energy to destroy DNA molecules in human skin and eyes--which is why overexposure can lead to skin cancer and the development of cataracts.

Unlike many other types of solar radiation which are visible to the human eye, the shortest wave-lengths--or ultraviolet rays--are invisible. These UV rays are divided by scientists into three groups according to their wavelength and relative hazard to human health:

UV-A rays = These are the longest of the three UV wavelengths. They contribute to premature aging, wrinkling of the skin, sunburns, and various forms of skin cancer.

UV-B rays = These are stronger than UV-A and pose a much greater risk of skin cancer than UV-A. UV-B rays are more intense in the summer, and at higher altitudes and when closer to the equator. They are the most common cause of sunburns, and often cause premature aging, skin cancer, cataracts, and immune system disorders.

UV-C rays = These are the shortest and most dangerous of the three UV wavelengths. However, nearly all UV-C races are absorbed by the Earth's atmosphere.

Dangers of Ultraviolet Radiation:

While a small amount of exposure to sunlight can be healthy and pleasurable, too much can be dangerous. Exposure to UV rays is linked to a number of harmful health effects.

Skin Cancer and Skin Damage: Since the middle of the century, the incidence of skin cancer cases has increased rapidly. In fact, sun bathing and tanning only began to be fashionable in the 1920's and 1930's. Prior to this time, people considered untanned skin as a status symbol, indicating they did not have to work outdoors. Today, medical researchers divide people into six skin types: Types I and II usually have blue, green or hazel eyes, and blond or red hair and freckles, and have a very high risk of getting skin cancer. Type I never tans and always burns, and Type II tans minimally. Those who have dark skin, including most blacks, are Type V or VI. Light skinned people are much more likely to develop skin cancer than dark skinned people—with the incidence rate of malignant melanoma in whites about twenty-fold that of blacks in the U.S.

Some effects of sunlight on the skin are visible within hours or days (e.g.: sunburn and tanning); other effects are delayed and cumulative and may be seen in months to years (e.g.: skin cancer and photo aging). Eighty percent of the UV exposure occurs before the age of 18 and the damage is cumulative over time.

Premature Aging: Sun exposure also causes premature aging of the skin. As much as 90% of the signs of aging, such as wrinkles and loss of elasticity, are actually caused by the sun. Photo aging of the skin is different than normal chronological aging. Regular sun bathers show photo aging changes early in life (before 30 years of age); while chronologically aged skin shows changes later (after 40 or more years of age). Freckling, fine wrinkling, and dilatation of capillaries are often seen early in the photo aging process; later on the photoaged skin develops irregular pigmentation, often called liver spots. Both photo aging and chronological aging causes wrinkling and loss of skin elasticity; however, they occur much earlier when the skin has been overexposed to the sun.

Cataracts and Eye Disorders: Cataracts are a leading cause of blindness worldwide. For example, in the United States cataracts affect about 1% of the population--or about 2.6 million people--and cause about 9% of all blindness. However, in India cataracts affect about 4% of the population--or about 35.8 million people--and cause about 55% of all blindness. UV exposure is one of the risk factors in the development of cataracts. Corneal sunburn, growths on the outer surface of the eye, and other eye diseases are also known or suspected to be related to long-term exposure to UV radiation. While dark-skinned people are less likely to develop skin cancer, dark-eyed people are more likely to develop cataracts. The suggested reason is because dark eyes have more of the dark pigment, melanin, which absorbs more solar radiation, leading over time to more damage to the lens of the eye.

Immune System Damage: While an understanding of how UV radiation causes the suppression of the immune system is only now emerging, it appears that specific cells in human skin play a role in human immune response. In some people--and especially those with weakened immune systems--UV-B appears to destroy or further weaken these protective immune cells, thus reducing the body's defenses against certain diseases. For these individuals, UV-B may also interfere with the effectiveness of immunizations administered through the skin.

The UV Index

In response to the increasing incidence of skin cancer, cataracts, and other health problems caused by exposure to the sun's harmful ultraviolet radiation, the National Weather Service (NWS), the U.S. Environmental Protection Agency (EPA), and the Center for Disease Control and Prevention (CDC) have developed an Ultraviolet (UV) Index to help people prevent overexposure to the sun' harmful rays. This UV Index is derived from ozone data via satellite observations, atmospheric pressure, temperature forecasts, and expected cloudiness. It is issued by the National Weather Service every day for 58 U.S. cities (including Salt Lake City) for the one-hour period around noon the following day. The UV Index is as follows:

Index Value Exposure Level
0-1   Minimal
3-4   Low
5-6   Moderate
7-9   High
10+  Very High

Based on the above UV Index, fair skinned (Type II) people can burn (around noon time) within the following amount of time:

Index Value Burn Time (Fair Skin)

0-2   60 minutes
3-4   45 minutes or more
5-6   30 minutes
7-9   15-24 minutes
10+  10 minutes or less

Also, the NWS, EPA and CDC have issued the following description of skin phototypes:

Never Tans/Always Burns: Skin color in unexposed area: pale or milky white; alabaster. Tanning history: develops red sunburn; painful swelling; skin peels.

Sometimes Tans/Usually Burns: Skin color in unexposed area: very light brown; sometimes freckles. Tanning history: usually burns; pinkish or red coloring appears, can gradually develop light brown tan.

Usually Tans/Sometimes Burns: Skin color in unexposed area: light tan, brown, or olive; distinctly pigmented. Tanning history: infrequently burns; shows moderately rapid tanning response.

Always Tans/Rarely Burns: Skin color in unexposed area: brown, dark brown, or black. Tanning history: rarely burns, shows very rapid tanning response.

Common-Sense Approach to Sun Exposure

Although the thinning ozone layer and increased outdoor activity are reasons for health experts to be concerned, no one is advocating that Americans avoid the sun. Rather, medical associations, such as the American Academy of Dermatology and Skin Cancer Foundation, recommend that people adopt a common-sense approach to being outdoors, and offer the following suggestions:

Minimize sun exposure at midday when the sun’s rays are the strongest.

Liberally apply a sunscreen that protects you across the broadest range of UV-A and UV-B sunlight. When the UV Index is Moderate, wear at least a SPF-15 or higher on all exposed parts of the body before going outdoors; or if the UV Index is High or Very High, wear at least a SPF-30.

Reapply the sunscreen often, even on cloudy days.

Wear protective clothing.

Wear a hat with a brim that shades the face.

Wear sunglasses that screen out (or block) UV radiation.

Never let children stay in the sun without adequate protection. (Because sunscreens should not be used on children under six months old, their sun exposure should be severely limited.)

Make sun protection a year-round activity, not just something practiced during the summer months.

Role of Reflective Surfaces

The role or reflective surfaces is also important in determining the amount of UV radiation people receive. Snow, sand and water all reflect UV rays and can intensify exposure. For example, fresh snow reflects 85% of UV radiation, white sand reflects about 18%, and water reflects about 5%. Obviously, lifestyle decisions can override other factors in determining a person’s risk from exposure to the sun. People who work or play outdoors for long periods of time are at greater risk of the harmful effects from UV exposure. Activities such as skiing, sunbathing, or swimming can lead to extremely high exposures.

Suntans and Tanning Parlors

The Environmental Protection Agency (EPA) has stated that the "use of tanning parlors also increases risk, because UV radiation from any source contributes to long-term damage" of a person's skin and health. Also, Dr. David Reuben, MD has written:

"A suntan is not a sign of health. It is a crude defense mechanism: your body's desperate--and always unsuccessful--attempt to protect you from damage that can be irreparable. Your system throws a dark curtain of pigment called melanin over you to keep dangerous UV radiation from doing even more harm. But it is too late. Once a suntan appears, the damage has already taken place. ...Exposure to ultraviolet rays...destroys the elastic fibers that keep healthy skin taut and supple. The tens of millions of women who have pursued that "fresh, young-looking" golden tan are discovering that years of sunbathing have left them with yellowed, sagging skin.

A particular danger to the eyes exist in tanning parlors, whose lamps emit large doses of dangerous UV light. According to the American Medical Association, "simply closing the eyes, using regular sunglasses or putting cotton balls over the eyes may not protect against eye damage." Many medical experts mince no words in their opinion of tanning parlors. Dr. Michael J. Franzblau, clinical associate professor of dermatology at the University of California at San Francisco School of Medicine, says, "No sane person should ever go into one." (David Reuben, "Suntan's Can Kill You," Readers Digest, June 1990, pp.119-123.)

Much of the information for this section originally appeared in the copyrighted book Utah's Weather and Climate, edited by Dan Pope and Clayton Brough, in 1996. UCCW Directors have received permission from the copyright owners of this book to reproduce such information on its website and to revise and updated it where appropriate.