  Superconducting transitions in the absence of magnetic field should be
non-hysteretic. Here we address the fact that the drops in electrical
resistance that have been interpreted as evidence of superconductivity in
several hydrides under high pressure (so-called "superhydrides") show
hysteresis. We argue that the experimental evidence shows that the observed
hysteresis cannot be attributed to experimental artifacts but is intrinsic to
the samples. Assuming that the drops in resistance signal a thermodynamic phase
transition, we argue that the presence of intrinsic thermal hysteresis
indicates that these are first order transitions, whereas for standard
superconductors the transition in the absence of applied magnetic field is
always second order. We conclude that this is another feature that
qualitatively distinguishes superhydrides from standard superconductors, in
addition to the ones that have been pointed out earlier [1,2], $assuming$ these
materials are superconductors. Alternatively and more likely, whether or not
the drops in resistance signal a thermodynamic phase transition, our analysis
indicates that superhydrides are not superconductors.
