title: Factors affecting SPF in vitro measurement and correlation with in vivo results.
abstract: OBJECTIVE
  The in vitro evaluation of SPF is still a problem due to the lack of repeatability and correlation between the in vitro and in vivo data, and many authors are currently working to develop an internationally harmonized method. Very recently, the use of several "adjuvant" ingredients such as boosters, antioxidants, immunomodulators, solvents and film-forming ingredients have further complicated the pattern for product developers that should frequently run in vivo test. The aim of this study was to understand whether a simple and cheap in vitro method could be optimized in order to provide both statistically repeatable and predictive SPF measurement.
  
  
  METHODS
  In vitro SPF assessments were carried out on 75 commercial products. The SPF was measured according to two laboratory methods (A and B), using different substrates (PMMA and surgical tape Transpore™), quantity of product and spectrophotometers. In order to evaluate whether a standard technique of spreading could lead to a statistically reliable result, we applied different spreading pressure (100 g and 200 g). Furthermore, we investigate whether other parameters characterizing the product (SPF category, filter and texture) might represent statically significant variables affecting the measures. We then compared the results obtained from in vitro SPF measure of 11 products to in vivo SPF, in order to assess the predictability of in vitro methods.
  
  
  RESULTS
  Several problems were encountered in confirming the weakness of the in vitro procedures. Pressure, SPF category, filter and texture did not affect significantly the results. Overall best results were obtained with the B2 method that in terms of repeatability and predictivity provided statistically better results. Method A with Transpore™ tape showed better in vitro-in vivo correlation than Method B with PMMA plates.
  
  
  CONCLUSIONS
  In our investigation, we demonstrated that it is possible for a single laboratory to optimize internal methods and protocols to achieve repeatable and predictive in vitro results, but it is extremely difficult to develop methods reproducible and equally reliable in different laboratories, probably due to "external variables" (e.g. environmental, operator), which are difficult to control.
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.
authors: A
authors: A
authors: Dimitrovska Cvetkovska
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.|School of Pharmacy, Master Course in Cosmetic Science and Technology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.|Ambrosialab srl, via Mortara 171, Ferrara, 44121, Italy.
authors: S
authors: S
authors: Manfredini
authors: Ambrosialab srl, via Mortara 171, Ferrara, 44121, Italy.
authors: P
authors: P
authors: Ziosi
authors: Ambrosialab srl, via Mortara 171, Ferrara, 44121, Italy.
authors: S
authors: S
authors: Molesini
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.
authors: V
authors: V
authors: Dissette
authors: Ambrosialab srl, via Mortara 171, Ferrara, 44121, Italy.
authors: I
authors: I
authors: Magri
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.
authors: C
authors: C
authors: Scapoli
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.
authors: A
authors: A
authors: Carrieri
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.|School of Pharmacy, Master Course in Cosmetic Science and Technology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.
authors: E
authors: E
authors: Durini
authors: Department of Life Sciences and Biotechnology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.|School of Pharmacy, Master Course in Cosmetic Science and Technology, University of Ferrara, via L. Borsari 46, Ferrara, 44121, Italy.|Ambrosialab srl, via Mortara 171, Ferrara, 44121, Italy.
authors: S
authors: S
authors: Vertuani
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D013056:Spectrophotometry, Ultraviolet; D059405:Sun Protection Factor; D013473:Sunscreening Agents / Q000737:chemistry*; D055815:Young Adult
chemical_list: D013473:Sunscreening Agents
keywords: 
  SPF 
  in vitro
  ; claim substantiation; formulation; spectroscopy; sunscreens