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The Effects of Ultraviolet Light (Sun Damage)
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The Effects of Ultraviolet Light

Richard Thomas, MD, FRCPC

When we first started learning about the negative effects of overexposure to the sun, sunscreens were developed. The earliest sunscreens protected our skin from sunburns by blocking out UVB lights. This allowed us to stay in the sun longer, but this unfortunately resulted in increased exposure to UVA lights to which the earlier sunscreens were ineffective against. Modern sunscreens are called broad spectrum, protecting our skin from both UVA and UVB lights. It needs to be said, however, that not all broad spectrum sunscreens protect us from the entire range of ultraviolet light however.

Sunlight exposure has both positive and negative effects on the skin. The positive effects are vitamin D production, and a sense of warmth and pleasure. However, there are many negative effects, short and long term that need to be recognized and protected against.

Short-term negative effects:

  • Sunburn/Tan
  • Light aggravated conditions
  • Photosensitive rashes
  • Allergic reactions
  • Drug and checmical photo toxicity

Medium-term negative effects:

Long-term effects:

Ultraviolet light can be generally categorized as UVA or UVB light, and refer to the different wavelengths, and have varying characteristics.

UVA Light:

  • 320-400nm
  • Levels of UVA is consistent throughout the year regardless of season
  • UVA penetrates into the lower dermis of the skin
  • Penetrates glass
  • 95% of UVL is UVA
  • Causes tanning of the skin
  • Immunosuppressive
  • An important contributor to melanoma
  • Cause of most aging effects on the skin, such as wrinkling
  • Causes many photodermatoses
  • Cause of phototoxic reactions to various drugs
  • The light that sun-beds mainly use. Remember that there is no such thing as a safe sun tan. The FDA is currently investigating whether suntan beds should be banned for people under the age of 18.

UVB Light:

  • 290-320nm
  • Levels of UVB light increase during the summer, at noon, and are higher on the equator
  • Can only penetrate the surface layer, the epidermis
  • Does not go through glass
  • SPF of sunscreens are determined by the amount of UVB that it blocks
  • More carcinogenic than UVA
  • Causes sunburns on the skin
  • Required for Vitamin D production

Sunscreens are the first and foremost defence to sun damage. First, you will need to choose the right sunscreen.


SPF,   sun damage,   sunburn,   sunscreen,   suntan,   UVA,   UVB,