Let $M$ be a compact smooth manifold equipped with a positive smooth density $��$ and $H$ be a smooth distribution endowed with a fiberwise inner product $g$. We define the Laplacian $��_H$ associated with $(H,��,g)$ and prove that it gives rise to an unbounded self-adjoint operator in $L^2(M,��)$. Then, assuming that $H$ generates a singular foliation $\mathcal F$, we prove that, for any function $��$ from the Schwartz space $\mathcal S(\mathbb R)$, the operator $��(��_H)$ is a smoothing operator in the scale of longitudinal Sobolev spaces associated with $\mathcal F$. The proofs are based on pseudodifferential calculus on singular foliations developed by Androulidakis and Skandalis and subelliptic estimates for $��_H$.

21 pages