The sunburn index—which is also known as the UV index—was developed by the National Weather Service and the Environmental Protection Agency as a way to provide people with information as to the varying risks of sunburn on particular days. Ranging in scale from 0 to 10 (10 being the riskiest), the index is calculated based on several factors: day of the year, latitude, elevation, cloud cover, and ozone levels. People with fair skin should be the most cognizant of the UV index when venturing outside, though people with tan or dark complexions should not ignore it either. The table below explains the index in more detail.
UV radiation can damage the skin within minutes, depending on exposure. A strong sunscreen with a high SPF is recommended by most doctors for this reason.