  Since b quark mass is not asymptotically large, chirally enhanced corrections
which arise from twist-3 wave functions may be important in B decays. We thus
evaluate the hadronic matrix elements with the final light pseudoscalar mesons
described by leading twist and twist-3 distribution amplitudes. We find that
chirally enhanced corrections can be included consistently in the framework of
QCD factorization only if the twist-3 distribution amplitudes are symmetric. We
then give explicit expressions of $a_i^p$ for $B \to \pi\pi$ at the
next-to-leading order of $\alpha_s$ including chirally enhanced corrections. We
also briefly discuss the divergence appeared in the hard spectator
contributions.
