Outdoor sports and risk of skin lesions

MADAM, With interest we read the study by Mahé et al. about the difference in the number of ultraviolet (UV) radiationrelated skin lesions in children playing outdoor sports and children who did not. Indeed, as the incidence of UV radiation-related skin lesions is increasing, it is important to identify risk factors in order to guide preventive actions. However, we have reasons to believe that the study design prohibits drawing the conclusion that ‘outdoor sports increase the risk of developing UV radiation-induced skin lesions in childhood’. As data about sport activities were only collected in 2009, the design of this study is essentially cross-sectional. With this design it is only possible to show an association between UV radiation-related skin lesions and outdoor sports, and not the causal relation which is implied by the authors. This is especially of importance as the authors did not control for any confounders in their analysis (e.g. skin colour, playing outside). Therefore, other factors may have played a substantial role in the association between outdoor sports and UV radiation-related skin lesions, and the difference found may be overestimated. Furthermore, the assumption that ‘children who practised at least one sport always or sometimes played outside’ may be too optimistic. Future studies should therefore not focus on larger groups, as suggested by the authors, but rather on a different study design, for example a cohort study. Regular follow-up moments should be planned to determine the frequency and degree of outdoor sports, so that the true relation between outdoor sports and UV radiation-induced skin lesions can be determined.