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What is the UV Index?

Office of Air and Radiation (6205J); July 2006; EPA430-F-06-014

Some exposure to sunlight can be enjoyable; however, too much could be dangerous. Overexposure to the sun’s ultraviolet (UV) radiation can cause immediate effects, such as sunburn, and long-term problems, such as skin cancer and cataracts. The UV Index, which was developed by the National Weather Service and the U.S.  Environmental Protection Agency (EPA), provides important information to help you plan your outdoor activities to prevent overexposure to the sun’s rays.

The UV Index provides a daily forecast of the expected risk of overexposure to the sun. The Index predicts UV intensity levels on a scale of 1 to 11+, where 1 indicates a low risk of overexposure and 11+ signifies an extreme risk. Calculated on a next-day basis for every ZIP Code across the United States, the UV Index takes into account clouds and other local conditions that affect the amount of UV radiation reaching the ground in different parts of the country.

UV Index Number Exposure Level
2 or less Low
3 to 5 Moderate
6 to 8 High
8 to 10 Very High
11+ Extreme

SunWise action steps

By taking a few simple precautions daily, you can greatly reduce your risk of sun-related illnesses. To be SunWise, consider taking the following action steps daily:

Early detection of melanoma can save your life. Carefully examine ALL of your skin once a month. A new or changing mole in an adult should be evaluated by a dermatologist.

What is the UV Alert?

EPA issues a UV Alert when the level of solar UV radiation reaching your local area is predicted to be unusually intense for the time of year. The UV Alert is a warning, and it offers simple steps you can take to protect yourself and your family. The UV Alert consists of the SunWise action steps and is posted by ZIP Code and City, State at www.epa.gov/sunwise/uvindex.html.

What does the UV Alert mean?

The UV Alert is based on the UV Index, which EPA provides with the support of the National Weather Service. EPA only issues a UV Alert when the UV Index is predicted to be 6 or higher and unusually intense for the time of year. In some parts of the United States, the UV Index rarely or never reaches this level, so your local area may never receive a UV Alert.

UV Alert days are not the only days you need to protect yourself. EPA recommends that you take the SunWise action steps every day, regardless of the season. Because children typically spend more time outdoors than adults, it is especially important that children take these steps. Even if you have darker skin, EPA recommends that you act SunWise to reduce your risk of skin cancer, cataracts, and other UV-related health problems.

Where can I find the UV Index and UV Alert forecasts for my area?

You can find the UV Index and UV Alert forecasts for your area by visiting EPA’s SunWise Web site at www.epa.gov/sunwise/uvindex.html. Enter your ZIP Code. The resulting UV forecast will indicate if there is a UV Alert.

The SunWise Web site will direct you to EPA’s EnviroFlash Web site, where you can sign up to receive the daily UV Index and occasional UV Alerts directly by e-mail. The National Weather Service is currently offering a national UV Alert map as an experimental product. The map indicates which parts of the country have a UV Alert forecast for the coming day. Follow the link from the SunWise Web site to the map.

While you should always take precautions against overexposure to the sun, please take special care to adopt the safeguards when the UV Index predicts levels of high or above. Watch for UV Index reports in your local newspapers, on television, and online, and remember to always be SunWise!

For more information, visit our Web site at www.epa.gov/sunwise.


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