Abstract: In this talk, I will discuss some consequences of the foreground complexity on CMB analysis. I will explain that, due to the variations of the physical conditions across our Galaxy, the foreground signal displays complex behaviors which needs to be accounted for. These behaviours include complex deviations of the SED of the EB spectra from the canonical one (e.g. a MBB), a difference between the SEDs of EE, EB and BB and a conversion of E modes into B modes .We should remain carefully aware of the existence of such effects to ensure that they do not impact our analysis of cosmic birefringence, especially as our datasets will become more and more sensitive.