Skip Navigation

The Sun and Your Skin

About UV

UV rays are invisible waves of radiation generated by the sun. While some of the sun's radiation is in the form of visible light and heat, UV rays are shorter in length and are invisible. UV radiation is present every day, even when it's cloudy.

UV radiation is recognized by the U.S. Department of Health and Human Services, the Occupational Safety and Health Administration (OSHA), the Environmental Protection Agency (EPA) and other agencies as a known human carcinogen - it is on the same list as cigarettes and asbestos. The sun's UV radiation can cause skin damage, eye damage and even skin cancer.UVA causes aging, UVB causes burning

Types of UV Rays

There are three classifications of UV rays based on their wavelengths. Each of these wavelengths affects the skin differently. We are concerned about UVA and UVB.

  • UVA rays have the longest wavelength and account for 95% of the UV that reaches us at the earth's surface. UVA penetrates the deep layers of the skin (dermis), and is responsible for skin tanning, aging, wrinkles, and skin cancer.
  • UVB rays are shorter, and account for just 5% of the UV that reaches us. UVB penetrates the upper layer of the skin (epidermis), and causes sunburn and skin cancer.
  • UVC rays are the shortest of all. They are completely absorbed by ozone in the atmosphere, so they never reach us.

When UV rays penetrate the skin, they can damage the DNA inside the skin cells. While the body can usually repair the damage, sometimes this mechanism fails, resulting in the development of cancerous cells. UV rays can also damage the structure of the skin, leading to:

  • Sunburn
  • Freckles
  • Wrinkling
  • Dark blotches
  • Rough texture
  • Skin thinning and sagging

UV Intensity

6 key factors influence the intensity of UV light:

Time of Year: The sun's angle varies with the seasons, causing the intensity of UV rays to change. UV intensity tends to be highest during the summer months.

Time of Day: The amount of UV varies throughout the day. The period of highest danger is between 10 a.m. and 4 p.m. When your shadow is shorter than you are, you are being exposed to high levels of UV rays.

Scattered and Reflected UV Rays: UV rays reflect off snow, water, sand, and concrete. Thin cloud cover scatters UV rays in all directions and allows UV rays to reach your skin even when you are wearing a hat or are under an umbrella.

Altitude: UV rays are more intense at higher altitudes because the thinner atmosphere filters out fewer UV rays. UV rays increase approximately 5% with every 1,000 feet above sea level. For example, a mountain at 10,000 feet receives 50% more UV exposure than an area at sea level.

Latitude: UV rays are strongest close to the equator because the sun is more directly overhead. In regions that are farther from the equator, the UV rays enter the ozone layer at an angle, which decreases UV intensity.

Climate/Weather: Clouds block some UV rays from hitting the earth and decrease the UV intensity. However, clouds only block 20-40% of damaging UV rays. That means that 60-80% of UV rays are still reaching your skin.

The UV Index can help you plan for a sun safe day. You can find it in your local newspaper, or online at the EPA's website. Our Scheduling page will help you learn how to read the UV Index and use it to plan for a sun safe day.

How can overexposure to UV rays be avoided?

We cannot stay completely out of the sun (nor would we want to!). There are many occasions to be outdoors for exercise, work, or recreation. It is easy to protect yourself from UV radiation without restricting your activity.

  • Get in the habit of planning for sun protection every time you are spending time outdoors. Learn about all of the different prevention strategies so that you can determine which ones are appropriate for your activities.
  • Check the UV Index forecast and follow the accompanying EPA recommendations
  • Limit sun exposure between 10 a.m. and 4 p.m.
  • Seek shade when available
  • Cover up by wearing a wide-brimmed hat, long-sleeved shirt, long pants and sunglasses
  • Use sunscreen with SPF 30 or higher, and lip balm with SPF 15 or higher