title: The influence of the amount of sunscreen applied and its sun protection factor (SPF): evaluation of two sunscreens including the same ingredients at different concentrations.
abstract: BACKGROUND
  To estimate labeled sun protection factor (SPF) for sunscreen, the amount of product applied on volunteers, according to food and drug administration (FDA) and International protocols, is 2 mg/cm(2). However, different studies have shown that consumers actually apply much less product when exposed to the sun. Previous studies have reported contradictory findings in an attempt to correlate the amount applied in relation to SPF. The objective of the present study was to estimate the influence of the quantity of sunscreen applied in the determination of SPF, according to the FDA methodology.
  
  
  METHODS
  Forty volunteers were included in two groups (SPF 15 and 30). The selected sunscreen was then applied in four different quantities (2, 1.5, 1.0 and 0.5 mg/cm(2)). All areas were irradiated with a solar simulator. After 24 h, the minimal erythemal dose (MED) and SPF were determined.
  
  
  RESULTS
  In both groups, we observed that the SPF decreased when the amount of sunscreen applied was decreased. The differences between the 2 mg/cm(2) area and the others were significant in both groups (P<0.001). The correlation between specified SPF and applied amount grew exponentially.
  
  
  CONCLUSIONS
  The protection provided by sunscreen is related to the amount of product applied. It is essential to educate consumers to apply larger amounts of sunscreen for adequate photoprotection.
authors.affiliation: Department of Dermatology, Hospital das Clínicas, University of São Paulo, São Paulo, SP, Brazil. medci004@terra.com.br
authors.forename: Sergio
authors.initials: S
authors.lastname: Schalka
authors.forename: Vitor Manoel Silva
authors.initials: VM
authors.lastname: dos Reis
authors.forename: Luis Carlos
authors.initials: LC
authors.lastname: Cucé
mesh_terms: D000293:Adolescent; D000328:Adult; D054626:Consumer Health Information / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012878:Skin Neoplasms / Q000517:prevention & control; D013472:Sunlight / Q000009:adverse effects*; D013473:Sunscreening Agents / Q000494:pharmacology*
chemical_list: D013473:Sunscreening Agents