We review the basic setup of Kaluza–Klein theory, namely a five-dimensional vacuum with a cyclic isometry, which corresponds to Einstein–Maxwell-dilaton theory in four-dimensional spacetime. We first recall the behaviour of Killing horizons under bundle lift and projection. We then show that the property of compact surfaces of being (stably) marginally trapped is preserved under lift and projection provided the appropriate (‘Pauli’) conformal scaling is used for the spacetime metric. We also discuss and compare recently proven area inequalities for stable axially symmetric two-dimensional and three-dimensional marginally outer trapped surfaces.