A NONINVASIVE MEASURE OF PHOTOAGEING

Background. Photoageing develops in skin due to chronic sun exposure and a method of measuring photoageing would be useful in monitoring solar damage in populations, in studies of sun exposure as an aetiological agent, and in the evaluation of the effects of cosmetics and therapeutics. Methods of measuring photoageing include several invasive techniques as well as non-invasive techniques which are often difficult to use and have not been validated. The non-invasive measure of photoageing described here is a new method for grading silicone-rubber casts of the skin surface. This paper describes the development of the measure (named the Sigma system) and compares its reliability and validity with the most widely-used similar measure (the Beagley and Gibson system). Methods. Useable punch biopsies and silicone-rubber casts were obtained from 82 subjects, Two random subgroups of silicone casts were created and the first subgroup was used for the development of the Sigma system, while the second subgroup was used to test validity. All casts were graded twice using the Sigma system and twice using the Beagley and Gibson system by two observers. The gradings of the second subgroup of casts were compared with the degree of photoageing seen on histological examination of the biopsies. Results. The intraclass correlation coefficient (ICC) for inter-observer reliability of the Sigma system was 0.89, with 73 of the 82 casts graded at the same level of photoageing by the two observers. Intra-observer ICC were 0.84 and 0.87 for the two observers. The Goodman-Kruskal tau for agreement between the grade on the Sigma system and histological degree of photoageing was 0.22. While these values are very similar to the reliability and validity estimates obtained using the Beagley and Gibson system, the Sigma system is easier to learn and to use. Conclusions. The Sigma system is a reliable and easy-to-use measure of photoageing which has many possible applications in monitoring and studying the effects of solar exposure.