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Sunscreen

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Sunscreen, Sun Protection Factor, SPF, Titanium Dioxide, Zinc Oxide, Oxybenzone, Octinoxate, Menthyl Anthranilate, Avobenzone, Drometrizole

  • See Also
  1. Sun Exposure (lists other preventive measures)
  2. Sun Damaged Skin
  3. Phototoxic Reaction
  4. Sunburn
  • Technique
  1. Use Sunscreen with SPF of 15 or higher
    1. SPF 15-30 is typically sufficient protection
    2. SPF above 50 is unlikely to provide additional benefit
      1. No added protection or prolonged duration of activity
  2. Use Sunscreen that blocks UVA and UVB
    1. Most current Sunscreens block UVB
    2. SPF rating does not apply to UVA
    3. "Broad spectrum" denotes protection for both UVA and UVB
      1. Zinc Oxide
      2. Titanium Dioxide
      3. Drometrizole trisiloxane (Mexoryl)
  3. Shake Sunscreen well before using
  4. Avoid spraying Sunscreen on face
    1. Risk of inhalation
    2. Spray Sunscreen onto hands and then apply to face
  5. Wear Sunscreen on all outdoor daylight exposures
    1. Cloudy days: 80% UV radiation penetrates clouds
    2. Swimming: 50% UV radiation penetrates water
    3. High altitude (UVB increases 8-10% per 1000 feet)
    4. Exposure to snow or water (reflective surface)
  6. Apply 2-3 tablespoons (1 ounce) of Sunscreen for whole body
    1. Do not forget around eyes, ears and mouth
    2. Apply to scalp if bald or hair thinning
  7. Apply Sunscreen 15 minutes before exposure and then every 2 hours (regardless of SPF)
    1. Reapply Sunscreen every 1 hour when sweaty or wet
    2. Water resistant (or water proof) sun screens require the same frequent replacement when wet
  8. Protect babies and children well from Sun Exposure
    1. Keep infants under 6 months in shade or covered
    2. If unable to keep out of sunlight, use Zinc Oxide or Titanium Dioxide containing Sunscreen for maximal protection
  • Physiology
  1. Sun Protection Factor (SPF) ratio
    1. Time to produce slight erythema on suncreened skin to
    2. Time to produce same erythema without Sunscreen
  2. SPF Interpretation
    1. "Broad spectrum" denotes protection for both UVA and UVB
    2. SPF gives no information on Ultraviolet A protection
    3. SPF reflects protection from UVB Light
      1. SPF 15 blocks 93% of UVB
      2. SPF 30 blocks 97% of UVB
      3. SPF 50 blocks 98% of UVB
  • Preparations
  • Chemical or Organic Sunscreens
  1. Avobenzone (Parsol 1789)
    1. Absorbs both short and long wavelength Ultraviolet A
    2. Does not absorb Ultraviolet B (UVB)
    3. May be degraded by sunlight exposure
  2. Menthyl Anthranilate
    1. Absorbs shorter wave length Ultraviolet A
  3. Oxybenzone
    1. Absorbs shorter wave length Ultraviolet A
    2. Banned in Hawaii as of 2021 due to adverse effects to ocean wildlife (coral bleaching, reproduction)
  4. Octinoxate
    1. Absorbs UVB
    2. Banned in Hawaii as of 2021 due to adverse effects to ocean wildlife (coral bleaching, reproduction)
  • Preparations
  • Physical, Mineral or Inorganic opaque compounds (scatter light)
  1. Types
    1. Titanium Dioxide
    2. Zinc Oxide
  2. Nanoparticles
    1. All physical Sunscreens are classified as nanoparticle, even if they are advertised as "non-nano"
    2. None of the physical Sunscreens are absorbed through the skin regardless of size (nano or "non-nano")
    3. Nanoparticle Sunscreens are typically easier to apply
    4. Nanoparticle size may have environmental impact, but the effects are not currently known
  • Efficacy
  1. Reduced with wind, heat, humidity, and altitude
  2. Reduced with poor or inadequate application
    1. Most persons do not apply enough Sunscreen
    2. Multiple layers required to reach listed SPF
  3. Reduces Incidence of Actinic Keratoses
    1. Thompson (1993) N Engl J Med 329:1147 [PubMed]
    2. Naylor (1995) Arch Dermatol 131:170 [PubMed]
  4. Decreases photoaging
  • Safety
  1. Regular use does not result in Vitamin D Deficiency
  2. Oxybenzone, Zinc Oxide and Titanium Dioxide are safe on skin
  • Resources
  • References
  1. (2018) Presc Lett 25(7):39
  2. (2013) Presc Lett 20(7):41-2
  3. Potera (1997) Physician and Sports Med 25(5):117-20
  4. (1999) Med Lett Drugs Ther, 41(1052): 43-4 [PubMed]
  5. Wentzell (1996) Am Fam Physician 53(5):1713-19 [PubMed]