Summer Initiation of Ruxolitinib in Vitiligo: Natural Phototherapy Confounds the Seasonal Signal

This letter comments on the recent real-world study by Marzano et al. evaluating topical ruxolitinib in non-segmental vitiligo. We raise a methodological concern regarding the interpretation of the seasonal treatment initiation effect, arguing that the superior early response observed in summer initiators may largely reflect unmeasured ambient UV exposure rather than a true drug–UV synergy. We propose that target trial emulation using propensity score matching could reduce confounding and yield more robust estimates in future analyses.