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Ultraviolet Light Rays (UVA and UVB)

The sunlight that reaches the earth has ultraviolet A and ultraviolet B (UVA and UVB) rays. These ultraviolet rays are the main causes of damage to the skin from the sun. UVA and UVB rays affect the skin's sensitivity to sun exposure in different ways.

UVA:

  • Can pass through window glass.
  • Is not affected by a change in altitude or weather.
  • Is present all day and every day of the year.
  • Penetrates deep into skin layers.
  • Is 20 times more abundant than UVB rays.
  • Causes long-term skin damage.

UVB:

  • Cannot pass through window glass.
  • Causes sunburn.
  • Causes tanning.
  • Helps the body make vitamin D.
  • Is more intense:
    • During the middle of the day.
    • In the summer.
    • At high altitudes and near the equator.
  • Can cause skin cancer and cataracts.

Use a sunscreen that has a sun protection factor (SPF) of at least 15 or higher. Sunscreens that say "broad-spectrum" can protect the skin from ultraviolet A and B (UVA and UVB) rays. Sunscreens come in lotions, gels, creams, and ointments.

By Healthwise Staff
Primary Medical Reviewer William H. Blahd, Jr., MD, FACEP - Emergency Medicine
Specialist Medical Reviewer H. Michael O'Connor, MD - Emergency Medicine
Last Revised September 1, 2011

WebMD Medical Reference from Healthwise

Last Updated: September 01, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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