A Guide to the UV Index and Sun-Safe Behavior
While some exposure to sunlight is enjoyable, too much can be dangerous, causing immediate effects like blistering sunburns and longer-term problems like skin cancer and cataracts. Overexposure also causes wrinkling and aging of the skin, and scientists are concerned that UV may even impair the human immune system.
The sun gives out energy over a broad spectrum of wavelengths. Ultraviolet (UV) radiation, which has a shorter wavelength than either visible blue or violet light, is responsible for sunburn and other adverse health effects. Fortunately for life on earth, stratospheric ozone screens most harmful UV radiation. However, what gets through the ozone layer can cause a number of problems, particularly for people who spend substantial time outdoors:
Because of these adverse health effects, you should limit your exposure to UV radiation and protect yourself when working, playing or exercising outdoors.
Types Of Uv Radiation
Scientists have classified UV radiation into three types - UVA, UVB, and UVC.
The stratospheric ozone layer absorbs some but not all of these types of UV:
UVA Not absorbed by the ozone layer
UVB Partially absorbed by the ozone layer
UVC Completely absorbed by the ozone layer
UVA and especially UVB penetrate the surface of the skin and can cause the adverse health effects listed above.
The ozone layer forms a thin shield in the stratosphere, protecting life on earth from the sun's harmful ultraviolet (UV) rays. In the 1980s, scientists began accumulating evidence that the ozone layer was being depleted. Depletion of the ozone layer can result in increased UV radiation reaching the earth's surface, which can lead to greater chance of overexposure to UV and the consequent health effects, including skin cancer, cataracts, and immune suppression
How Stratospheric Ozone Protects Us
Ozone is a naturally occurring gas found in the earth's atmosphere that absorbs certain wavelengths of the sun's UV radiation. Ozone is concentrated in a part of the atmosphere called the stratosphere. Stratospheric ozone is most concentrated between 6-30 miles above the earth's surface.
Ozone is formed when oxygen molecules absorb UV radiation and split apart into two oxygen atoms (O), which combine with other oxygen molecules (02), to form ozone molecules (03). Ozone is also broken apart as it absorbs UV radiation. In this way, UV helps sustain the natural balance of ozone in the stratosphere, while ozone in turn absorbs UV, protecting life on earth from harmful radiation.
How Ozone Is Depleted
Chlorofluorcarbons (CFCs) are used widely in industry and elsewhere as refrigerants, insulating foams, and solvents. They migrate into the upper atmosphere after use. Because they are heavier than air, they have to be carried by air currents into the stratosphere, a process that can take as long as 5 to 10 years. These chemicals absorb UV radiation, break apart, and react with ozone, taking one oxygen atom away and forming highly reactive chlorine monoxide. Chlorine monoxide (C 0) in turn breaks down 03 again by pulling away a single oxygen atom, creating two 02 molecules, and allowing the C to move freely to another ozone molecule. In this way each chlorine atom acts as a catalyst, repeatedly combining with and breaking apart as many as 100,000 ozone molecules during its stratospheric life.
Americans love the sun, and spend increasing amounts of time outside working, playing, exercising - often in clothing that exposes a lot of skin to the sun. Most people are now aware that too much sun has been linked to skin cancer, but few know the degree of risk posed by overexposure, and fewer are aware that the risks go beyond skin cancer. Recent medical research has shown that overexposure to the sun's ultraviolet (UV) radiation can contribute to serious health problems.
This section provides a quick overview of the major problems linked to UV exposure: skin cancer (melanoma and non-melanoma), other skin problems, cataracts, and immune system suppression. Understanding these risks and taking a few sensible precautions (described in this booklet) will help you to enjoy the sun while lowering your chances of sun-related health problems later in life.
Melanoma, the most serious form of skin cancer, is also one of the fastest growing types of cancer in the U.S. Many dermatologists believe that there may be a link between childhood sunburns and malignant melanoma later in life. Melanoma cases in this country have almost doubled in the past two decades, with at least 32,000 new cases of melanoma and 6,900 deaths estimated for 1994 alone. The rise in melanoma cases and deaths in America is expected to continue.
Melanoma can spread to other parts of the body quickly, but when detected in its earliest stages it is almost always curable. If not caught early, melanoma is often fatal.
Melanoma begins as an uncontrolled growth of pigment-producing cells in the skin. This growth leads to the formation of dark- pigmented malignant moles or tumors, called melanomas. Melanomas may suddenly appear without warning, but may also develop from or near a mole. For that reason it is important to know the location and appearance of moles on the body so any change will be noticed. Melanomas are found most frequently on the upper backs of men and women, and the legs of women, but can occur anywhere on the body. Be aware of any unusual skin condition, especially a change in the size or color of a mole or other darkly or irregularly pigmented growth or spot; scaliness, oozing, bleeding or change in the appearance of a bump or nodule; spread of pigment from the border into surrounding skin; and change in sensation including itchiness, tenderness, or pain.
Non-Melanoma Skin Cancers
Unlike melanoma, non-melanoma skin cancers are rarely fatal. Nevertheless, they should not be taken lightly. Untreated, they can spread, causing more serious health problems. An estimated 900,000 Americans developed non-melanoma skin cancers in 1994, while 1,200 died from the disease.
There are two primary types of non-melanoma skin cancers:
Basal Cell Carcinomas are tumors of the skin which usually appear as small, fleshy bumps or nodules on the head and neck, but can occur on other skin areas as well. It is the most common skin cancer found among fair-skinned people. Basal cell carcinoma does not grow quickly, and rarely spreads to other parts of the body. However, it can penetrate below the skin to the bone and cause considerable local damage.
Squamous Cell Carcinomas are tumors which may appear as nodules or as red, scaly patches. The second most common skin cancer found in fair-skinned people, squamous cell carcinoma is rarely found in darker-skinned people. This cancer can develop into large masses, and unlike basal cell carcinoma, it can spread to other parts of the body.
These two non-melanoma skin cancers have high cure rates - as high as 95 percent if detected and treated early. The key is to watch for signs and to detect the cancer in its early stages.
Basal cell carcinoma tumors usually appear as slowly growing, raised, translucent, pearly nodules which, if untreated, may crust, discharge pus, and sometimes bleed. Squamous cell carcinomas usually are raised, red or pink scaly nodules or wart- like growths that form pus in the center. They typically develop on the edge of the ears, the face, lips, mouth, hands and other exposed areas of the body.
These sun-induced skin growths occur on body areas exposed to the sun. The face, hands, forearms, and the "V" of the neck are especially susceptible to this type of blemish. They are pre-malignant, but left untreated, actinic keratoses can become malignant. Look for raised, reddish, rough-textured growths. See a dermatologist promptly if you notice these growths.
Chronic exposure to the sun causes changes in the skin called actinic, or solar, degeneration. The skin over time becomes thick, wrinkled, and leathery. This condition has often been referred to as "premature aging" of the skin. Since it occurs gradually, often manifesting itself many years after the majority of a person's exposure to the sun, photoaging is often regarded as an unavoidable condition, a normal part of growing older. With proper protection from UV radiation, however, photoaging can be substantially avoided.
Cataracts and Other Eye Damage
Cataracts are a form of eye damage, a loss of transparency in the lens which clouds vision. Left untreated, cataracts can rob people of vision. Research has shown that UV radiation increases the likelihood of certain cataracts. Although curable with modern eye surgery, cataracts diminish the eyesight of millions of Americans, and necessitate millions of dollars of eye surgery each year. Other kinds of eye damage include: pterygium (tissue growth on the white of the eye that can block vision), skin cancer around the eyes, and degeneration of the macula (the part of the retina near the center, where visual perception is most acute). All of these problems could be lessened with proper eye protection from UV radiation.
Scientists have found that sunburn can alter the distribution and function of disease-fighting white blood cells in humans for up to 24 hours after exposure to the sun. Repeated exposure to UV radiation may cause more long-lasting damage to the body's immune system. Mild sunburns can directly suppress the immune functions of human skin where the sunburn occurred, even in people with dark skin.
Too Much Sunlight Can Be Dangerous...
Excessive sun exposure can result in painful sunburn, but can also lead to other serious health problems, including melanoma, a life-threatening form of skin cancer. Melanoma is one of the fastest growing forms of cancer in the U.S. In addition to melanoma, excessive UV exposure can lead to premature aging of the skin, cataracts, non-melanoma skin cancers, and immune system suppression.
BE SUN WISE
Protecting yourself from overexposure to UV radiation is simple if you take the precautions listed below.
Wear Sunglasses That Block 99-100% of UV Radiation
Sunglasses that provide 99-100% UVA and UVB protection will greatly reduce sun exposure that can lead to cataracts and other eye damage. Check the label when buying sunglasses.
Wear a Hat
A hat with a wide brim offers good sun protection to your eyes, ears, face, and the back of your neck - areas particularly prone to overexposure to the sun.
Protect Other Areas Of Your Body With Clothing During Prolonged Periods in the Sun
Tightly-woven, loose-fitting clothes are best, but any clothing is better than none at all.
Always Use a Sunscreen When Outside on a Sunny Day
A sunscreen with a Sun Protection Factor (SPF) of at least 15 blocks most harmful UV radiation. Apply sunscreen liberally and reapply every two hours when working, playing, or exercising outdoors. Even waterproof sunscreen can come off when you towel off sweat or water. Children under six months of age should never have sunscreen applied to their skin, but should be protected by avoiding too much time outdoors.
Avoid the Midday Sun As Much As Possible
The sun's UV rays are strongest between 10 a.m. and 4 p.m. To the
extent you can, limit exposure to the sun during these hours.
Avoid Sunlamps and Tanning Parlors
Sunbeds damage the skin and unprotected eyes and are best avoided entirely.
Watch For the UV Index
The UV Index provides important information to help you plan your outdoor activities in ways that prevent overexposure to the sun's rays. Developed by the National Weather Service (NWS) and the Environmental Protection Agency (EPA), the UV Index is issued daily in selected cities across the U.S.
Special Considerations For Children...
Although many of the sun's worst effects do not appear until later in life, recent medical research has shown that it is very important to protect children and teenagers from overexposure to UV radiation. The majority of most people's sun exposure occurs before age 20, and studies increasingly suggest a link between early exposure and skin cancer as an adult.
Helping Children Be Sun Wise
Take special care with children, since they spend more time outdoors than adults and can burn more quickly. The precautions described in this booklet can help ensure that the children around you avoid UV-related health problems, both now and later in life. Started early and followed consistently, each of these steps will become an easy, accepted habit, no more bothersome than fastening seatbelts every time you drive the car.
How NWS Calculates The Uv Index
The National Weather Service (NWS) uses a computer model to calculate the next day's UV levels for selected cities across the United States. The model takes into account a number of factors, including the amount of ozone and clouds overhead, latitude, elevation, and time of year.
To compute the UV Index forecast, the model first calculates a UV dose rate, or amount of UV radiation to which a person will be exposed at the next day's solar noon (when the sun is highest in the sky) under "clear sky" (no clouds) conditions.
The UV dose rates obtained from the model are then adjusted for the effects of elevation and cloud cover at specific locations. Higher elevations will increase the UV dose rate because there is less atmosphere to absorb and scatter UV rays. Greater cloud cover will tend to reduce the UV dose rate because clouds screen out some - but not all - UV rays.
The resulting value is the next day's UV Index forecast. The UV forecasts for selected locations are provided daily on a 0-10+ scale, where 0 indicates a minimal likely level of exposure to UV rays and 10+ means a very high level of exposure.
For More Information
To learn more about the UV Index and how to protect yourself from overexposure to the sun's UV rays, call EPA's Stratospheric Ozone Hotline at (800) 296-1996. Hotline staff can supply you with fact sheets and other useful information.