title: Effect of daily versus intermittent sunscreen application on solar simulated UV radiation-induced skin response in humans.
abstract: BACKGROUND
  Acute and chronic skin damage occurs as a consequence of solar UV radiation exposure. To diminish such skin damage, the dermatologic community advocates the daily use of sunscreens as part of a sun avoidance strategy.
  
  
  OBJECTIVE
  We determined the effectiveness of a sunscreen product with a sunscreen protection factor (SPF) of 15 applied daily in preventing UV-induced histologic damage in human skin compared with the protection afforded by sunscreens with equal or higher SPF applied intermittently.
  
  
  METHODS
  Twenty-four subjects were exposed to 2 minimal erythema doses of solar-simulated UV on 4 consecutive days. Three sunscreen products were applied to the buttock of each subject. One SPF 15 product was applied daily before exposure to UV and, to simulate intermittent product use, an SPF 15 or SPF 29 product was applied on 3 of 4 days, with one missed application on days 2, 3, or 4. Skin biopsy specimens were taken and processed for routine and immunohistochemical staining. Changes in number of sunburn cells and Langerhans cells as well as degree of inflammatory infiltrate and lysozyme immunostaining were determined.
  
  
  RESULTS
  There was a statistically significant increase in the number of sunburn cells, degree of inflammation, and intensity of lysozyme staining, and there was a decrease in the number of Langerhans cells at sites where sunscreen application was missed as compared with unirradiated control and daily SPF 15 sunscreen-treated sites.
  
  
  CONCLUSIONS
  Our data suggest that daily use of a sunscreen reduces the skin damage produced by UV exposure compared with intermittent use of equal or higher SPF products. The daily application of sunscreens in appropriate quantities reduces the harmful effects of solar UV radiation on skin. Compliance is essential for maximal benefit of sunscreens.
authors.affiliation: Department of Dermatology, Boston University Medical Center, and the Procter & Gamble Co, Sharon Woods Technical Center, Cincinnati, OH, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Phillips
authors.forename: J
authors.initials: J
authors.lastname: Bhawan
authors.forename: M
authors.initials: M
authors.lastname: Yaar
authors.forename: Y
authors.initials: Y
authors.lastname: Bello
authors.forename: D
authors.initials: D
authors.lastname: Lopiccolo
authors.forename: J F
authors.initials: JF
authors.lastname: Nash
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008875:Middle Aged; D012867:Skin / Q000187:drug effects* / Q000473:pathology / Q000528:radiation effects*; D013473:Sunscreening Agents / Q000008:administration & dosage*; D014466:Ultraviolet Rays
chemical_list: D013473:Sunscreening Agents