  We present a simple derivation of the one-loop trace anomaly in spinor QED
through dispersion relations, avoiding completely any ultraviolet
regularization. The anomaly can be expressed as a convergent sum rule for the
imaginary part of a relevant formfactor. In the massless limit, the imaginary
part produces a delta-function singularity at zero external momentum squared.
Such a treatment reveals an "infrared face" of the trace anomaly, in striking
similarity with the well-known case of the axial anomaly.
