title: Metal oxide sunscreens protect skin by absorption, not by reflection or scattering.
abstract: OBJECTIVE
  The inorganic metal oxide sunscreens titanium dioxide and zinc oxide have been considered to protect against sunburning ultraviolet radiation by physically reflecting/scattering the incident photons and thus protecting the skin. Earlier publications suggested, however, that the primary action of UV protection by these sunscreen agents is through absorption and not by reflection. The purpose of this work was to quantitate the contributions of each of these modes of action to the protection provided by inorganic UV sunscreen filters.
  
  
  METHODS
  An optical integrating sphere was used to measure the transmission and the reflectance of titanium dioxide and zinc oxide.
  
  
  RESULTS
  The average range of reflection for zinc oxide and titanium dioxide throughout the UV range was only 4-5% (less than SPF 2), providing minimal UV protection via this mechanism. The remainder of the UV protection is provided by semiconductor band gap mediated absorbance of the UV photons. At wavelengths above the semiconductor band gap absorption energy levels (in the long UVA and visible wavelengths), they are predominantly reflectors of light (up to 60% reflection) and non-absorbing.
  
  
  CONCLUSIONS
  Titanium dioxide and zinc oxide provide UV protection primarily via absorption of UV radiation and not through significant reflection or scattering.
authors.affiliation: Sun and Skin Consulting LLC, Ringoes, NJ, USA.
authors.forename: Curtis
authors.initials: C
authors.lastname: Cole
authors.affiliation: Johnson & Johnson Consumer and Personal Care Products Inc., Skillman, NJ, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Shyr
authors.affiliation: Johnson & Johnson Consumer and Personal Care Products Inc., Skillman, NJ, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Ou-Yang
mesh_terms: D006801:Humans; D008670:Metals / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D012867:Skin; D013473:Sunscreening Agents / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D008670:Metals; D010087:Oxides; D013473:Sunscreening Agents
keywords: absorption; anatase; band gap; barium sulfate; protection; reflection; rutile; scattering; sunscreen; titanium dioxide; ultraviolet radiation; zinc oxide