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 limi
t, the imaginary part produces a delta-function singularity at zero ex
ternal 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.