ABSTRACT
OBJECTIVE: The objective of this work was to investigate the utility of a new in vitro SPF test method in blinded ring-testing, against new ISO acceptance criteria. METHODS: Twenty four blinded, commercial, emulsion-type, primary sunscreen products, covering the full range of labelled SPF in Europe (SPF6 - 50+), were tested by three test institutes using the current ISO24444:2010 In Vivo SPF Test Method and simultaneously by three separate test laboratories using a new candidate in vitro SPF test method, developed under the leadership of Cosmetics Europe (CE). The resulting relationship between in vitro SPF and in vivo SPF values was then compared with acceptance criteria developed recently by the International Standards (ISO) TC217/WG7 Sun Protection Test Methods Working Group. RESULTS: Analysis of the mean inter-laboratory in vitro and mean inter-institute in vivo SPF values revealed a strong correlation between in vitro and in vivo values, with a Pearson correlation coefficient of r2 = 0.88 (P < 0.0001), a slope of 1.01 and a non-significant intercept (-1.48; P = 0.62). When these data were compared to the new ISO WG7 acceptance criteria, method bias was found to be extremely low and over 95% of the coupled data lay within the model 'funnel' (defined by upper and lower confidence intervals). CONCLUSION: In conclusion, the results of blinded ring testing and comparison to new ISO WG7 acceptance criteria indicate that a new in vitro SPF test method meets (and exceeds) these minimum criteria and is an interesting candidate for possible deployment as an industry test methodology.
ABSTRACT
BACKGROUND/PURPOSE: Sunscreen efficacy is usually expressed by the sun protection factor (SPF) which is calculated by establishing the minimum erythematous dose (MED), i.e. the smallest amount of energy required to trigger erythema. Efforts have been made to harmonise SPF testing but in vivo SPF methodology could still be improved to reduce its variability. This article proposes a means of standardising MED evaluations through the development and validation of an MED assessment system based on image analysis. METHODS: The MED assessment system comprises a camera combined with a black tube for acquiring pictures of the skin surface. Specific software was then developed to analyse these pictures to determine the MED based on the shape, size and colour of the exposed zones. The MED assessment system was validated through two studies. The first study was designed to assess the correlation between three expert graders who visually determined the MEDs in five subjects on whom three different suncare products (SPF 6, SPF 30 and SPF 50+) were tested. The second study correlated results obtained from one expert grader with those from a grader assisted by the new MED assessment system. RESULTS: Results of the first study showed substantial variation between graders, with kappa agreement as low as 0.59 (percentage error 19.7%). Results of the study assessing correlation between the expert grader and the grader facilitated by the new MED assessment device showed better correlation, with a kappa value of 0.75 and percentage error of 9.61%. CONCLUSION: A high degree of inter-grader variability was seen when MED was assessed by expert graders. The new MED assessment system provides background colour correction and standardisation to enable accurate MED determination. A high level of correlation was seen between the expert grader and the new MED assessment system, thus demonstrating its potential utility in more accurate and homogenous MED evaluations. Future multicentre studies are required to improve and validate the standardised MED determination for suncare products and to further evaluate the role of this new MED assessment system. However, these preliminary results are encouraging and may set the scene for this new MED assessment system to become the standard of the future.