title: Salicylic acid deposition from wash-off products: comparison of in vivo and porcine deposition models.
abstract: OBJECTIVE
  Salicylic acid (SA) is a widely used active in anti-acne face wash products. Only about 1-2% of the total dose is actually deposited on skin during washing, and more efficient deposition systems are sought. The objective of this work was to develop an improved method, including data analysis, to measure deposition of SA from wash-off formulae.
  
  
  METHODS
  Full fluorescence excitation-emission matrices (EEMs) were acquired for non-invasive measurement of deposition of SA from wash-off products. Multivariate data analysis methods - parallel factor analysis and N-way partial least-squares regression - were used to develop and compare deposition models on human volunteers and porcine skin.
  
  
  RESULTS
  Although both models are useful, there are differences between them. First, the range of linear response to dosages of SA was 60 μg cm(-2) in vivo compared to 25 μg cm(-2) on porcine skin. Second, the actual shape of the SA band was different between substrates.
  
  
  CONCLUSIONS
  The methods employed in this work highlight the utility of the use of EEMs, in conjunction with multivariate analysis tools such as parallel factor analysis and multiway partial least-squares calibration, in determining sources of spectral variability in skin and quantification of exogenous species deposited on skin. The human model exhibited the widest range of linearity, but porcine model is still useful up to deposition levels of 25 μg cm(-2) or used with nonlinear calibration models.
authors.affiliation: Ashland Specialty Ingredients, 1005 US Route 202/206, Bridgewater, NJ, 08807, U.S.A.
authors.forename: M A
authors.initials: MA
authors.lastname: Davies
mesh_terms: D000818:Animals; D008954:Models, Biological; D020156:Salicylic Acid / Q000737:chemistry*; D013552:Swine
chemical_list: D020156:Salicylic Acid
keywords: chemical analysis; fluorescence; multiway partial least squares; parallel factor analysis; spectroscopy; statistics