title: Sun protection factor persistence during a day with physical activity and bathing.
abstract: OBJECTIVE
  The persistence of sunscreens during a day with physical activity and bathing is often debated. We wished to examine the durability of the protection achieved by one sunscreen application.
  
  
  METHODS
  Seven areas were marked on the back of 24 volunteers. One area was phototested to determine UV sensitivity. Six areas were treated with either an organic or an inorganic sunscreen (2 mg/cm2). The participants performed physical activities, were exposed to a hot environment and bathing during 8 h and were phototested with ultraviolet-B (UVB) radiation 30 min, 4 and 8 h after sunscreen application. The minimal erythema dose (MED) was determined 24 h after irradiation. The sun protection factor (SPF) was calculated, as MED on protected skin/MED on unprotected skin.
  
  
  RESULTS
  The SPFs of the inorganic and organic sunscreen, respectively, were reduced by 38% and 41% after 4 h and by 55% and 58% after 8 h.
  
  
  CONCLUSIONS
  One application of either an inorganic or an organic sunscreen reduced the erythema caused by UVB during a day with physical activity and bathing. After 8 h the sunscreens still provided approximately 43% of the initial protective effect. This might simulate what happens during a day at the beach.
authors.affiliation: Department of Dermatology, Bispebjerg Hospital, Copenhagen, Denmark.
authors.forename: Mette
authors.initials: M
authors.lastname: Bodekaer
authors.forename: Annesofie
authors.initials: A
authors.lastname: Faurschou
authors.forename: Peter Alshede
authors.initials: PA
authors.lastname: Philipsen
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D000328:Adult; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D013471:Sunburn / Q000517:prevention & control*; D013472:Sunlight / Q000009:adverse effects; D013473:Sunscreening Agents / Q000494:pharmacology*; D013550:Swimming
chemical_list: D013473:Sunscreening Agents