UV Index Fact Sheet: National UV Index and Health Effects of Excessive UV Exposure

Health Effects of Excessive UV Exposure

Background

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.

UV Indexes

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.

uvindex.gif

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:

example fo daily uv index

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:

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.

Preventive Measures:

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/

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