  Helicity of quarks and gluons inside the proton at small Bjorken $x$ is one
of the missing pieces of the proton spin puzzle, with limited experimental
results due to various challenges. To address the problem, we derive under the
framework of color glass condensate (CGC) effective theory a renormalization
group equation in rapidity for the parton helicity distributions, which resums
double-logarithmic factor, $\alpha_s\ln^2(1/x)$, with $\alpha_s$ being the
strong coupling constant. With running coupling, the equation produces results
at Bjorken $x\leq 0.1$ that are consistent with the world polarized scattering
data. There is an evidence for a significant parton helicity contribution from
the small-$x$ region. However, the helicity estimate still contains a large
uncertainty that will dramatically reduce with the upcoming measurements from
the Electron-Ion Collider (EIC). Ongoing attempts to reduce the uncertainty of
our helicity prediction in the medium term will also be discussed.
