  Particles with millicharge q and sub-eV mass can be produced in photon-photon
collisions, distorting the energy spectrum of the Cosmic Microwave Background.
We derive the conservative bound q < 10^-7 e (as well as model-dependent bounds
two orders of magnitude stronger), incompatible with proposed interpretations
of the PVLAS anomaly based on millicharged production or on
millicharged-mediated axion-like couplings.
