UV Radiation

Ultraviolet or UV radiation is found in the sun's invisible rays, the ones that cause sunburns and sometimes skin cancer. There are three types of ultraviolet rays:

  • UV-A
    These rays stay fairly constant throughout the year and also penetrate more deeply into the skin's layers than other rays. UV-A rays contribute to premature aging and wrinkling of the skin, sunburn, and even skin cancer.
  • UV-B
    These rays, which are stronger than UV-A, are more intense in summer months, at higher altitudes, and closer to the equator. UV-B is the most common cause of sunburn. It can also contribute to premature aging of the skin and can cause cataracts—a permanent clouding of the eye that greatly reduces vision. The UV-B exposure you get over the course of your life can even cause skin cancer or weaken your immune system.
  • UV-C
    These rays, although the strongest and most dangerous, do not generally reach the earth. They are normally filtered out by the earth's ozone layer.

How much UV radiation reaches me?

The amount of UV radiation that reaches you on earth depends on the following:

  • Time of day: UV radiation is greatest when the sun is highest in the sky—generally midday, between 10 AM and 4 PM. UV radiation is lower in the early morning and late afternoon. A good rule to follow is: "If your shadow is shorter than you are, you should take extra care in the sun."
  • Season: While UV exposure is usually highest during the summer (May-August), it is important to remember that UV rays reach the earth every day. Remember to take steps to protect yourself and your family all year round, even on cloudy days.
  • Altitude: The air is cleaner and thinner at higher altitudes; therefore, UV exposure is greater in the mountains than in the valleys.
  • Where you live: UV radiation is strongest at the equator and gets weaker as you move towards the earth's poles. When you travel to tropical locations close to the equator, be sure to use maximum protection!
  • Length of time spent in the sun: The longer you are out in the sun, the more UV radiation you receive. Many of us forget to count the time we spend outside doing daily activities such as walking the dog, getting the mail, or walking to a train or bus. However, much of the UV radiation we receive is from these types of activities.
Glossary
Ozone Layer
A region of the upper atmosphere (about 10 to 20 miles in altitude) that contains a high concentration of ozone that absorbs many of the ultraviolet rays from the sun.
UV Radiation
Invisible rays from the sun. UV radiation can burn the skin and cause melanoma and other types of skin cancer. UV radiation that reaches the earth's surface is made up of two types of rays: UVA and UVB. UVA rays pass deeper into the skin and UVB rays are more likely to cause sunburn. Both kinds of radiation are believed to cause skin cancer and cause premature aging of the skin. People should use sunscreens that block or absorb both kinds of UV radiation.
UV-A Rays
Rays of the sun that maintain a relatively constant intensity throughout the year and contribute to premature aging and wrinkling of the skin, sunburn, and skin cancer.
UV-B Rays
Rays of the sun that are more intense in summer months, at higher altitudes, and closer to the equator.
UV-C Rays
The strongest and most dangerous of the sun's rays that are normally filtered by the ozone layer.