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We present a theoretical analysis into the fundamental physical mechanisms contributing to backscattering in hollow-core antiresonant fibers. We consider Rayleigh scattering originating from the hollow regions of the fiber, which may be filled with gases, Rayleigh scattering from within the glass membranes, as well as the contribution from scattering at the glass surfaces. We derive expressions for the backscattering coefficient into any specified guided mode for an arbitrary excitation. These lead to general scaling relations with the core size and wavelength, which are found to be the key parameters for backscattering, regardless of the exact antiresonant geometry. For a nested antiresonant hollow-core fiber with a core diameter of 35 µm, the only antiresonant fiber geometry for which the experimental data are available in the literature, we find that the surface-scattering limited backscattering coefficient of the fundamental mode into itself is nearly 40 dB below that of a single mode fiber, in good agreement with recently published measurements.