title: Accumulation of sunscreen in human skin after daily applications: a study of sunscreens with different ultraviolet radiation filters.
abstract: OBJECTIVE
  Sunscreen applied to the skin provides a considerable sun protection factor (SPF) even after 8 h. Sunscreen use for consecutive days may therefore result in an accumulation of the product. This study investigated the consequences of accumulation for SPF.
  
  
  METHODS
  Two sunscreens, one containing organic and one containing particle ultraviolet radiation (UVR) filters (SPF 30) (2 mg/cm(2)), were used. Areas on the back of 22 volunteers were applied with sunscreen on 5 consecutive days, once daily (12 volunteers) and three times daily (10 volunteers), and phototested. The SPF was determined on Days 1, 3 and 5.
  
  
  RESULTS
  One daily application of sunscreen did not result in an accumulation in the skin that significantly affected the SPF. However, three daily applications provided a significantly higher SPF for both the organic (mean SPF 1.56) and particle (mean SPF 2.45) sunscreen at Day 5 compared to Day 1 (P = 0.023 for both sunscreens).
  
  
  CONCLUSIONS
  Sunscreens accumulate in the skin when applied in the recommended amounts three times daily. In conjunction with other sun protection strategies, sunscreen application on consecutive days prior to UVR exposure can result in a basic skin protection, which may help to prevent severe sunburns on sun holidays.
authors.affiliation: Department of Dermatology, Bispebjerg Hospital, Copenhagen, Denmark. mettebodek@hotmail.com
authors.forename: Mette
authors.initials: M
authors.lastname: Bodekær
authors.forename: Ulf
authors.initials: U
authors.lastname: Akerström
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012867:Skin / Q000378:metabolism* / Q000473:pathology; D013471:Sunburn / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D013473:Sunscreening Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D013997:Time Factors; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D013473:Sunscreening Agents