Sun Protection
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þ See also:
  Sunburn: <B-Sun.TXT>

þ Types of UV light
 - UVA:UVB 1000:1
 - UVA:
  + used to be thought harmless
  + now known to be synergystic with UVB
  + responsible for sking aging, solar lentigines, actinic keratoses, basal
    cell and squamous carcinomas
  + penetrates deeper than UVB or UVA
  + tanning beds are UVA
  + because of diffusion through atmosphere, even distribution throughout day
 - UVB:
  + known to be harmful, most sunscreens screen only against this
  + peaks when shadows are short, usually 11AM-1PM
  + major cause of sunburn, but UVA exposure is synergystic
  + known cause of melanoma
 - UVC:

þ Melanin and Tanning
 - Dark skin is somewhat protective against UV damage
 - Tanning may offer some protection -- but tanning also results in DNA
   damage.

þ Sunburn
 - 2 episodes of severe sunburn as a child increases doubles adult risk of
   non-melanoma skin cancer
 - families that recognize risk of sun exposure and have their under-18 kids
   use sun protection have a 78% less risk of skin cancer

þ Melanoma
 - 32,000 cases a year, 7.000 deaths a year
 - men:  back and face; women: back of legs

þ Sunscreen
 - Clothing: hold up against lightbulb
  + if can see images through it, SPF of < 15
  + if can see light through it, SPF of 15-60
  + if can't see light, SPF >50
 - Glass: blocks UVB but NOT UVA

þ SPF
 - means how much it increases the Minimal Erythema Dose (MED)
 - will be soon replaced by better measure by U.S. FDA
 - SPF of 4 means that, if get sunburn in 30' in certain conditions, will
   get sunburn in 2 hours with SPF 4 sunscreen on.
 - note that this means protection from UVB, says NOTHING about UVA protection
 - SPF equivalence:
  + SPF 15: blocks 92% of UVB
  + SPF 30: blocks 96.7% of UVB
  + SPF 40: blocks 97.5% of UVB