UV Index

The UV Index is a measure of the intensity of the sun’s ultraviolet radiation in the sun burning spectrum. As the UV Index increases, the sun’s rays can affect your skin, eyes and immune system.  Therefore, you need to take more precautions to protect yourself from the harmful rays.

Developed by the National Weather Service (NWS) and EPA, the UV Index predicts the next day's ultraviolet radiation levels on a 0-10+ 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.

UV Index Number	Exposure Level	Minutes to burn
0 to 2	Minimal	60
3 to 4	Low	45
5 to 6	Moderate	30
7 to 9	High	15
10+	Very High	10

Ultraviolet (UV) Rays
Sunlight contains three types of ultraviolet rays: UVA, UVB, and UVC.

• UVA rays cause skin aging and wrinkling, and contribute to skin cancer, such as melanoma.  Because UVA rays pass effortlessly through the ozone layer (the protective layer of atmosphere, or shield, surrounding the earth), they make up the majority of our sun exposure.  Beware of tanning beds because they use UVA rays to generate tanning.  A UVA tan does not help protect the skin from further sun damage; it merely produces color and a false sense of protection from the sun.
• UVB rays are also dangerous, causing sunburns, cataracts (clouding of the eye lens), immune system damage, and contributing to skin cancer.  Melanoma, the most dangerous form of skin cancer, is thought to be associated with severe UVB sunburns that occur before the age of 20.  Most UVB rays are absorbed by the ozone layer, but enough of these rays pass through to cause serious damage.
• UVC rays are the most dangerous, but fortunately, these rays are blocked by the ozone layer and don't reach the earth.

Melanin
Melanin is the protective chemical in the skin that absorbs UV rays and causes tanning.   It is found in a variety of colors and concentrations, resulting in different skin colors.  Most people have a blending of melanin colors in their skin but tend to have a dominant shade:

• red, found primarily in Northern Europeans
• yellow, found primarily in Asians
• brown, found primarily in African, Native and South American, and South Pacific people

Yellow and red melanin found in light-skinned persons provide the least amount of sun protection.  Brown melanin found in darker-skinned persons reflects the most UV and provides the most sun protection.   Both dark- and light-skinned people need protection from UV rays because any tanning or burning causes skin damage.  Everyone should always wear sunscreen with a minimum SPF of 15.

Next

What is UV Radiation?

UV Index

Effects of Sunlight

Guidelines for Protection

Sun Quiz