We compute the critical temperature for the chiral transition in the background of a magnetic field in the linear sigma model, including the quark contribution and the thermomagnetic effects induced on the coupling constants at one-loop level. We show that the critical temperature decreases as a function of the field strength. The effect of fermions on the critical temperature is small and the main effect on this observable comes from the charged pions. The findings support the idea that the inverse magnetic catalysis phenomenon receives a contribution due only to chiral symmetry effects independent of the deconfinement transition.