Both the spin- and charge-density waves in Cr alloys are produced by the Coulomb attraction between electrons and holes on two nested Fermi surfaces. The Coulomb interaction responsible for the charge-density wave increases the energy splitting between quasiparticles which are strongly and weakly bound to the spin-density wave. If the splitting is sufficiently large, the paramagnetic-to-commensurate transition becomes strongly first order, as observed in CrFe and CrSi alloys.