  We compute the damping rate of a fermion in a dense relativistic plasma at
zero temperature. Just above the Fermi sea, the damping rate is dominated by
the exchange of soft magnetic photons (or gluons in QCD) and is proportional to
$(E-\mu)$, where E is the fermion energy and $\mu$ the chemical potential. We
also compute the contribution of soft electric photons and of hard photons. As
in the nonrelativistic case, the contribution of longitudinal photons is
proportional to $(E-\mu)^2$, and is thus non leading in the relativistic case.
