We show that locally bounded, local weak solutions to certain nonlocal, nonlinear diffusion equations modelled on the fractional porous media and fast diffusion equations given by \(\begin{aligned} \partial _t u + (-\Delta )^s(|u|^{m-1}u) = 0 \quad \text{ for } \quad 0<s<1 \quad \text {and}\quad m>0 \end{aligned}\) are locally Hölder continuous. We work with bounded, measurable kernels and provide the corresponding \(L^{\infty }_{loc} \rightarrow C^{0,\alpha }_{loc}\) De Giorgi-Nash-Moser Theory for the equation via a delicate analysis of the set of singularity/degeneracy in a geometry dictated by the solution itself and a careful analysis of far-off effects. In particular, our results are in the spirit of interior regularity, requiring the equation to hold only locally, and thus are new even for positive solutions of the equation with constant coefficients.
