UV Index Fact Sheet: National UV Index and Health Effects of Excessive UV Exposure
Increasing concern is being expressed by healthcare professionals, public health leaders and voluntary health organizations worldwide about the rapid increase in skin cancers and potential eye and immune system damage as a result of excessive ultraviolet (UV) exposure from the sun and other sources. The ozone layer shields the Earth from harmful ultraviolet (UV) radiation. Ozone depletion, as well as seasonal and weather variations, cause different amounts of UV radiation to reach the Earth at any given time.
Environmental leaders in Congress have called for the development of a nationwide public information program about sunsafe activities, and for the formulation of a national UV Index by the U.S. National Weather Service (NWS), in cooperation with the U.S. Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention (CDC).
Beginning June 28, 1994, an experimental UV Index was implemented by the National Weather Service, covering 58 cities in the United States. Evaluation of the program took place in the fall of 1994, and the experiment proved to be a success in terms of accuracy, format and use. View the daily UV Index predictions in the United States.
Until now, the United States has not had a national UV Index.
Currently, Canada, New Zealand, Sweden, Finland, the Netherlands, the United Kingdom, Norway and Germany either already have or are generating a UV forecast or a UV Index.
Several states, cities and medical institutions, however, developed similar indexes for their regions prior to the development of the national index. For instance, Hawaii has a UV Index; the State of Maine is establishing an index; M. D. Anderson Cancer Center in Houston, Texas has developed a successful regional index; dermatologists in New York have developed an informal index; and other indexes exist in Arizona, San Diego, New Orleans and Chicago.
According to the National Weather Service, there also are UV Indexes being produced by several private meteorology groups/private companies such as ACCU-Weather/Bausch & Lomb, and WSI Corporation/Orbital Sciences. Efforts will be made through the World Meteorological Organization to standardize these different indexes; that will, of course, take some time.
What Is the UV Index?
The National Weather Service (NWS) has provided the following information about the UV Index.
- The UV Index has been developed by the NWS, with the support of the U.S. Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention (CDC). NWS has taken responsibility for the creation of the product and the science supporting it, while the EPA is responsible for public education and outreach, with assistance from the CDC.
- The intent of the UV Index program is to enhance public awareness of the harmful effects of overexposure to the sun's ultraviolet rays, and to provide the public with specific actions they can take to reduce the likelihood of harmful effects of overexposure, which may include skin cancer, cataracts and immune system suppression.
- The daily predictions of UV intensity are related to potential health effects using a measure of the sunburning potency over the noon hour. The Index is conservatively calculated based on effects on skin types that burn easily. A conservative measure is appropriate because although not everyone sunburns easily, people of all skin types can experience other effects of UV exposure which include cataracts, immune system suppression and the potential for skin cancers, aging and wrinkling of the skin. Exposure levels reported by the Index are presented below:
Index Value Exposure Level
0 to 2.........................Minimal
3 to 4.........................Low
5 to 6.........................Moderate
7 to 9.........................High
10 +...........................Very High
- The UV Index predicts the next day's ultraviolet intensity at the Earth's surface over the one-hour period around solar noon. To derive the UV Index, ozone data from satellite observations, upper level pressure and temperature forecasts and expected cloudiness are scaled to produce a range of roughly 0-10+ from the North Pole to the Equator.
Index Value and Exposure Levels/Types of Skin
It should be noted that the Index values are meant to be reflective of the overall problem, not solely one of exposure for one particular skin type.
However, as it is necessary to give a specific number, the National Weather Service has chosen UV effects on skin Type II, that which usually burns easily and tans minimally. (There are at least four categorical systems for defining skin types; the Food and Drug Administration, the American Academy of Dermatology, the Skin Cancer Foundation, and the Environmental Protection Agency all have slightly different categorical systems. However, the description of skin Type II is generally the same in all.)
Exposure levels and index values are related in this way:
- Minimal: Index reading of 0 to 2 indicates minimal danger from the sun's UV radiation for the average (Type II) person. Most people can stay in the noon sun for up to one hour without burning.
- Low: Index reading of 3 to 4 indicates low risk of harm to the skin from the sun's radiation; Type II individuals can experience a burn in 30-60 minutes.
- Moderate: Index reading of 5 to 6 indicates some significant risk of skin damage due to the sun. Unprotected exposure can result in a burn in only 20-30 minutes.
- High: Index reading of 7 to 9 indicates high risk of harm from unprotected exposure to the sun. Time in the sun should be limited during midday (10:00 a.m. to 4:00 p.m.) since skin may burn in as little as 13-20 minutes.
- Very High: Index reading of 10 to 15 indicates very high risk of harm from unprotected sun exposure. Between 10:00 a.m. to 4:00 p.m. the length of time to burn may be less than 13 minutes without protection.
Ultraviolet Radiation and the Stratospheric Ozone Layer
The sun's rays reach the Earth as visible light, infrared light and ultraviolet (UV) light. UV is the shortest wavelength component of the solar spectrum. While moderate exposure to sunlight can be healthy and pleasurable, too much can be dangerous; exposure to UV rays, especially UVB, is linked to a number of harmful health effects. The atmosphere acts as an efficient filter to remove part of the UVB rays; an abundance of ozone in the stratosphere limits the quantity of UVB which reaches the Earth's surface and protects humans and other living matter from its potentially damaging effects.
Factors That Determine an Individual's Exposure
Exposure to UV radiation varies with the time of day, season of year, latitude and altitude. Weather conditions also affect the amount of UV that reaches the Earth. Much of the UV radiation reaches the Earth's surface even on slightly overcast or cloudy days. During very overcast or rainy days, UV rays are largely blocked out. Water, sand and snow, however, all reflect UV rays and can intensify exposure.
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 are at greater risk. Activities such as skiing, sunbathing or swimming can lead to extremely high exposures. Use of tanning parlors also increases risk, because UV radiation from any source contributes to long-term damage.
People with different skin types are affected differently. It is important to note that all skin, regardless of pigmentation, can be affected by UV.
Ultraviolet Radiation and Adverse Health Effects
Dermatologists report that:
- Without appropriate sunscreens or clothing to protect human skin, UV radiation can exert potent biological effects. Overwhelming evidence indicates that the skin can be damaged by direct exposure to natural or artificial sources of UV radiation, particularly UVB. Adverse health effects linked to UV exposure include skin cancers and measurable suppression of the immune system.
- The skin, according to researchers, is a major site of immunologic activity and UVB is capable of interfering with the human immune system via its effect on the skin. UVB-induced immune suppression appears to play a role in weakening the body's immune defense against skin cancer, in blocking effective immunity against infectious diseases and in interfering with immunizations administered through the skin. Certain medications (including diuretic, antibiotic and chemotherapy drugs) can make the skin more sensitive to sunlight; therefore, increased UV radiation can result in increases in adverse drug reactions with skin damage. UVB-induced immune changes also can play a significant role in exacerbating autoimmune diseases such as systemic lupus erythematosus.
- Cosmetic problems also can occur. Chronic exposure to UV radiation, starting in childhood, typically results in a change in the skin's texture. This leads to excessive wrinkles and variable degrees of skin thickening and thinning. After years of excessive exposure, the sun weakens the skin's elasticity, leaving the appearance of sagging cheeks and deeper than normal facial wrinkles. People who work or bask in the sun for years without sunscreen protection usually develop this tough, leathery skin that may make them look 15-to-20 years older. In addition, the sun can cause skin discoloration -- red, yellow, gray or brown blotches, formation of "liver spots," and gray scaly growths called actinic keratoses which may develop into cancer. It should be emphasized that these changes are not just due to recent exposure, but to cumulative effects throughout a lifetime. Special attention should be paid to the protection of children who tend to have longer outdoor exposure and may not show the effects of sun damage until much later in life.
- Skin pigmentation can afford individuals some degree of protection from the UV radiation effects of skin cancer, photoaging and immune system suppression; however, all races, even those with a high degree of skin pigmentation, can become immunosuppressed by UV radiation from a few hours of summer sun, despite minimal or no skin redness.
Prevent Blindness America, the American Academy of Ophthalmology, and the American Optometric Association state that:
Ultraviolet radiation can play a contributory role in the development of various eye disorders including age-related cataract, pterygium (growth of tissue on the white of the eye), cancer of the skin around the eye, photokeratitis (sunburn of the cornea) and corneal degenerative changes, and may contribute to age-related macular degeneration. Cataracts are a major cause of visual impairment and blindness worldwide.
How Can Skin Be Protected From Excessive UV Radiation?
- If a person is fair-skinned, or has relatives who have had skin cancer, unnecessary sun exposure should be avoided. If it is necessary to spend time in the sun, protective clothing with a tight weave, long-sleeved shirts, and hats with brims should be worn to help reduce the effects of ultraviolet rays. Direct exposure between 10 a.m. and 4 p.m., when the sun's rays are strongest, should be avoided. Most damaging exposure to sunlight occurs before the age of 20. Infants under 6 months of age should always be kept out of the sun, and young children should be taught sun protection at the earliest possible age. A sunscreen with a sun protection factor (SPF) of at least 15 should always be used. But even with sunscreen protection, no one should stay in the sun for long periods of time
- Sunscreens and sunblocks are applied to the skin to either absorb or reflect the sun's harmful rays. The absorbers are chemical agents and the reflectors are physical agents. The fairer the skin, the more this protection is needed, although it's important to everyone, regardless of skin type. A sunscreen with an SPF of at least 15 should always be used. The use of an effective sunscreen, or sunblock, may help reduce the chances of premature aging and wrinkling as well as reduce the incidence of skin cancer.
- Sunscreens should be applied approximately 20 minutes before every exposure to the sun, and should be reapplied frequently and liberally, at least every two hours, as long as time is spent in the sun. Sunscreens should always be reapplied after swimming or perspiring heavily.
- Sunscreens should be applied to ears, lips, nose and other areas that are especially prone to sunburn. Seventy to 80 percent of the sun's damaging rays can penetrate through cloudy haze and water, so a sunscreen should be used under those conditions as well. Sunscreens should also be used when out in the snow; sun reflected on snow can produce as much ultraviolet exposure as sun on sand, especially at higher altitudes.
How Can the Eyes Be Protected From UV Radiation?
A recent "Statement on Ocular Radiation Hazards in Sunlight" states:
- Ultraviolet radiation reaches the eye not only from the sky above but also by reflection from the ground, especially water, snow, sand and other bright surfaces. Protection from sunlight can be obtained by using both a brimmed hat or cap and UV absorbing eyewear. A wide-brimmed hat or cap will block roughly 50% of the UV radiation and reduces UV radiation that may enter above or around sunglasses. Ultraviolet absorbing eyewear provides the greatest measure of UV protection, particularly if it has a wraparound design to limit the entry of peripheral rays.
- Ideally, all types of eyewear, including prescription spectacles, contact lenses and intraocular lens implants should absorb the entire UV spectrum (UVB and UVA). UV absorption can be incorporated into nearly all optical materials currently in use, is inexpensive, and does not interfere with vision. The degree of UV protection is not related to price. Polarization or photosensitive darkening are additional sunglass features that are useful for certain visual situations, but do not, by themselves, provide UV protection.
- For outdoor use in the bright sun, sunglasses that absorb 99-100% of the full UV spectrum to 400 nm are recommended. Additional protection for the retina can be provided by lenses that reduce the transmission of violet/blue light. Such lenses should not be so colored as to affect recognition of traffic signals. The visible spectrum should be reduced to a comfortable level to eliminate glare and squinting. Individuals who also wear clear prescription eyewear outdoors should consider using lenses which absorb 99-100% of the UV radiation affecting the eyes.
- There is presently no uniform labeling of sunglasses that provides adequate information to the consumer. Labels should be examined carefully to insure that the lenses purchased absorb 99-100% of both UVB and UVA radiation. Consumers are advised to be wary of claims that sunglasses "block harmful UV rays" without saying how much.
The Diminishing Stratospheric Ozone Layer
Although many scientists have expressed concerns about the diminishing ozone layer and potential resulting health problems, that phenomenon is not primarily responsible for the present rise in skin cancer or the persistent appearance of other effects on the eyes and immune system. These effects result from cumulative exposure over time and are caused by many factors. Since World War II, the American public has increasingly been engaged in outdoor recreation activities, and thus exposed to more sunlight, as dramatic increases in personal income, vacation time and leisure activities have occurred. At the same time, swimming and leisure attire covering less of the body has become the norm and a "sun worshiping" culture has developed, especially among the young. As a result, tanning parlors have been widely frequented to provide tanning opportunities on cloudy days or in winter.
Consequently, the excessive exposure to UV rays resulting from changed personal behavior over the last 50 years has in large part caused the present public health problem. For example, the demographic group now at greatest risk for skin cancer is the over-50 Caucasian male population; their cumulative excessive exposure over time is now expressing itself. However, the seriousness of the diminishing ozone layer and its future potential public health implications should not be minimized.
The decrease in stratospheric ozone is primarily attributed to man-made chlorofluorocarbons (CFCs) and halons used in aerosols, refrigerants and other industrial products, as well as nitrous oxide which is a by-product of internal combustion engines and microbial degradation. These relatively stable compounds rise to the stratosphere where interaction of the compounds with UV radiation releases chlorine atoms. A single atom of chlorine binds to a molecule of ozone and destroys it; a single atom of chlorine may destroy up to 100,000 molecules of ozone before it eventually degrades after 75-100 years.
Numerous scientific reports have been published, clearly showing ozone layer depletion, especially over the poles; the health effects on humans as well as on animals and plants are not yet well understood.
Recent international agreements limiting the use of CFCs and other chemicals which harm the ozone layer should permit recovery to begin, but it is expected that there will be a 50-year delay until recovery.
About UV: ultraviolet radiation
Ultraviolet radiation is a portion of the electromagnetic spectrum with wavelengths shorter than visible light. The sun produces UV, which is commonly split into three bands: UVA, UVB, and UVC. UVA is not absorbed by ozone. UVB is mostly absorbed by ozone, although some reaches the Earth. UVC is completely absorbed by ozone and normal oxygen.
UVA: a band of ultraviolet radiation with wavelengths from 320-400 nanometers produced by the Sun UVA is not absorbed by ozone. This band of radiation has wavelengths just shorter than visible violet light.
UVB: a band of ultraviolet radiation with wavelengths from 280-320 nanometers produced by the Sun UVB is a kind of ultraviolet light that is particularly effective at damaging DNA. It is a cause of melanoma and other types of skin cancer. It has also been linked to damage to some materials, crops, and marine organisms. The ozone layer protects the Earth against most UVB coming from the sun. It is always important to protect oneself against UVB, even in the absence of ozone depletion, by wearing hats, sunglasses, and sunscreen. However, these precautions will become more important as ozone depletion worsens. An EPA fact sheet explains more about the health effects of increased UVB.
UVC: a band of ultraviolet radiation with wavelengths shorter than 280 nanometers UVC is extremely dangerous, but it is completely absorbed by ozone and normal oxygen (O2).
More Details Visit: http://www.epa.gov/