  Diffusion is a dissipative transport phenomenon ubiquitously present in
nature. Its details can now be analysed with modern effective field theory
(EFT) techniques that use the closed-time-path (or Schwinger-Keldysh)
formalism. We discuss the structure of the diffusive effective action
appropriate for the analysis of stochastic or thermal loop effects, responsible
for the so-called long-time tails, to all orders. We also elucidate and prove a
number of properties of the EFT and use the theory to establish the analytic
structure of the $n$-loop contributions to diffusive retarded two-point
functions. Our analysis confirms a previously proposed result by Delacr\'{e}taz
that used microscopic conformal field theory arguments. Then, we analyse a
number of implications of these loop corrections to the dispersion relations of
the diffusive mode and new, gapped modes that appear when the EFT is treated as
exact. Finally, we discuss certain features of an all-loop model of diffusion
that only retains a special subset of $n$-loop `banana' diagrams.
