  The Higgs portal of the Standard Model provides the opportunity for coupling
to a very light scalar field $\phi$ via the super-renormalizable operator
$\phi(H^\dagger H)$. This allows for the existence of a very light scalar dark
matter that has coherent interaction with the Standard Model particles and yet
has its mass protected against radiative corrections. We analyze ensuing
constraints from the fifth-force measurements, along with the cosmological
requirements. We find that the detectable level of the fifth-force can be
achieved in models with low inflationary scales, and certain amount of
fine-tuning in the initial deviation of $\phi$ from its minimum.
