Abstract. The study of interacting quantum fields in de Sitter geometry reveals peculiarities that are of conceptual and phenomenological interest. In this geometry, the exponential expansion of the metric produces an effective growth in the self-interaction of light fields, breaking down the standard perturbative expansion. Furthermore, in the massless limit the free propagators do not respect the symmetries of the classical theory, and neither do they decay at large distances. One way to avoid the problems of the standard perturbative calculations is to go to Euclidean de Sitter space, where the zero mode responsible for IR divergences can be treated exactly, giving an effective coupling $\sqrt{\lambda}$ for the perturbative corrections coming from the nonzero modes. The Lorentzian counterpart is then obtained by analytical continuation. However, we point out that a further partial resummation of the leading secular terms (which necessarily involves nonzero modes) is required to obtain a decay of the two-point functions at large distances for massless fields. We implement this resummation along with a systematic double expansion in $\sqrt{\lambda}$ and in $1/N$ in the $O(N)$ model. Finally, we discuss how these results compare with those known in the leading infrared approximation, obtained directly in Lorentzian de Sitter spacetime.