  Recently, the XENON1T experiment has observed an excess in the electronic
recoil data in the recoil energy range of $1$-$7$ keV. One of the most favored
new physics interpretations is electron scattering with a boosted particle with
a velocity of $\sim 0.1$ and a mass of $\gtrsim 0.1\,\mathrm{MeV}$. If such a
particle has a strong interaction with electrons, it may affect the standard
scenario of cosmology or be observed at low-threshold direct detection
experiments. We study various constraints, mainly focusing on those from the
big-bang nucleosynthesis, supernova cooling, and direct detection experiments.
We discuss the implication of these constraints on electron-scattering
interpretation of the XENON1T excess.
