Accurate knowledge of the amount of interstellar extinction and its properties is crucial to determine fundamental stellar parameters, such as luminosities, masses and ages. This can be challenging in case of young clusters surrounded by or embedded in the original molecular gas. NGC6530 is a rich young star forming region located towards a concentration of the native molecular gas. As a consequence, it is affected by a significant and variable reddening, as it has been reported in the literature, even with several hints of an anomalous reddening law. Several and also different literature results have been found about the reddening properties in this region. The Gaia-ESO survey data of NGC6530 gives us a uniq opportunity to address this issue. By using Gaia-ESO fundamental parameters and literature optical photometry, we derive the reddening law across the NGC6530 field. We find that both extinction and reddening show a spatial pattern that is consistent with the density map of the Lagoon Nebula, allowing us to trace its tridimensional structure. Our results are crucial for deriving other stellar properties and then understanding the star formation history of this cluster.