What is the UV Index?

By Samantha-Rae Tuthill, AccuWeather.com, Staff Writer
5/24/2012 9:37:21 AM

Skin Cancer Awareness

UV Index

May is Skin Cancer Awareness Month, so before you gear up to get outdoors and enjoy some of that beautiful late-spring weather it's important to take precautions to protect your skin.

The risk for damage comes from the sun's ultraviolet, or UV, rays, a kind of radiation that come in three different wavelengths. UVA rays can reach into the deeper layers of the skin, promote skin aging and wrinkles and are believed to increase the development of skin cancer. These rays come through whether the sun can be seen or not. Even when it's cloudy, or in the winter, UVA rays are around during all daylight hours at the same intensity. For many years UVA rays were thought to be safer than UVB rays, but new research points to UVA rays causing mutations in skin cell DNA , just different cells than are affected by UVB.

UVB rays are what cause sunburns and tans. These are also the rays that play the biggest role in skin aging and causing genetic skin cell damage that can lead to cancer. Unlike the UVA rays, UVB rays have varying times of intensity. The hours of 10 a.m. to 4 p.m. are the most dangerous, and more so from the months of April to October. Unlike the long wavelength UVA, and the mid-range UVB rays, UVC rays are shorter and do not reach the Earth's surface to contribute to cancer risks.

The UV Index exists to alert people of the level of solar radiation. Many factors go in to calculating the index for a particular area on a given day, including the elevation of the location, cloud coverage for that day, the amount of ozone in the atmosphere over that area and skin's sensitivity to UV radiation. The scale typically runs from 0-10, with 0 being the lowest risk of UV exposure (nighttime) to 10, when the conditions for radiation are at their peak. Ratings of 11 or higher are typically only used in areas where there is significant damage to the ozone layer. The higher the number, the more at risk you are, and the more safety measures you should be taking.

AccuWeather.com's UV Index shows your risk of radiation exposure.

To see the UV Index Forecast for your area, enter your city at AccuWeather.com's ultraviolet radiation page.

While your risks increase as the number on the UV Index goes up, it's important to protect yourself any time you go out into the sun for more than 20 minutes at a time. EarthGauge.net created this video of the four things you can do to keep yourself safe this summer.