Skin cancer is the most common form of cancer in the United States, taking thousands of lives every year. By the age of 70, one in five Americans will develop skin cancer. Now NASA is helping public health officials track the primary cause of the disease: overexposure to ultraviolet radiation.

The NASA Applied Sciences Program has partnered with the Centers for Disease Control and Prevention (CDC) to create the first publicly available map of ultraviolet (UV) radiation for all counties in the contiguous United States. The dataset, which spans 2005-2015, is available on the CDC’s National Environmental Public Health Tracking network, which delivers information and data about health issues related to environmental factors. Public health officials, city planners, or individuals concerned about Sun exposure can learn how much ultraviolet radiation is falling over each county each month, which is an important step in helping reduce skin cancer risks.

“Before this, there hasn’t been a true comprehensive exposure measure of UV radiation,” said Yang Liu, an associate professor at Emory University’s Rollins School of Public Health. “People have been studying Sun exposure using very crude indicators. We’re looking at the specific UV wavelengths that can cause skin cancer.”

Although skin cancer is caused by ultraviolet radiation, different types of UV radiation can have different effects. The two that play an important role in skin cancer are UVA and UVB rays. UVA rays penetrate deeply into the skin to cause genetic damage to cells; UVA is linked to long-term skin damage such as wrinkles. UVB are the principal rays that cause sunburn and can directly damage the DNA in skin cells.

The maps on this page show the average amount of UV radiation per square meter reaching the surface in different parts of the country. Liu and his team used an equation to combine the various wavelengths of UV radiation to mimic the intensity of a sunburn—a measurement called the “erythemally weighted daily dose.” The researchers also gave more weight to more populated areas. For instance, the measurement is higher in more populated areas, which is helpful for studying the corresponding population health effects of high UV exposure.