UV Index Overview
UV Index overview
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. The UV Index predicts ultraviolet radiation levels on a 1–11+ scale, helping people determine appropriate sun-protective behaviors. Several fact sheets explain the UV Index and steps you can take to minimize the risks from overexposure to the sun’s rays. The website will also display a UV Alert when the level of solar UV radiation is predicted to be unusually high and the risk of overexposure is greater.
Some exposure to sunlight can be enjoyable; however, too much can be dangerous. Overexposure to the sun’s UV radiation can cause immediate effects such as sunburn and long-term problems such as skin cancer and cataracts. The UV Index provides important information to help you plan outdoor activities and prevent overexposure.
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 minimal risk and 11+ means very high risk. Calculated on a next-day basis for dozens of cities 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.
Learn more about UV Index risk levels.
Sun safety tips
By taking a few simple precautions, you can greatly reduce your risk of sun-related illnesses:
- Limit your time in the sun between 10:00 a.m. and 4:00 p.m.
- Whenever possible, seek shade.
- Use a broad-spectrum sunscreen with a Sun Protection Factor (SPF) of at least 30.
- Wear a wide-brimmed hat and, when possible, tightly woven, full-length clothing.
- Wear UV-protective sunglasses.
- Avoid sunlamps and tanning salons.
- Check the UV Index daily.
While you should always take precautions against overexposure to the sun, take special care to adopt these safeguards when the UV Index predicts moderate levels or higher. Watch for UV Index reports in local newspapers and on television. For more information, visit EPA’s Sun Safety pages and the National Weather Service UV Index pages.