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 5% of the sun's rays.
- Is 20 times more abundant than UVB rays.
- Affects long-term skin damage.
UVB:
- Cannot pass through window glass.
- Causes sunburn.
- Causes tanning.
- Helps the body with normal vitamin D production.
- Varies with the season. It is more intense in the summer than in the winter.
- Varies with weather conditions.
- Is more intense at midday than in the morning or late afternoon.
- Is more intense at high altitudes and near the equator.
- Is 0.5% of the sun's rays.
- Is protected against by the sun protection factor (SPF) in sunscreens.
- Is related to more than 90% of non-melanoma skin cancer.
- Is related to cataracts.
Sunscreens that say "broad-spectrum" can protect the skin from both UVA and UVB rays. Sunscreens come in lotions, gels, creams, and ointments.
| Author: | Jan Nissl, RN, BS | Last Updated: February 7, 2008 |
| Medical Review: | William M. Green, MD - Emergency Medicine Alexander H. Murray, MD, FRCPC - Dermatology | |
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