We establish convolution inequalities for Besov spaces B s p,q and Triebel-Lizorkin spaces F s p,q . As an application, we study the mapping properties of convolution semigroups, considered as operators on the function spaces A s p,q , A ∈ {B, F }. Our results apply to a wide class of convolution semigroups including the Gauß-Weierstraß semigroup, stable semigroups and heat kernels for higher-order powers of the Laplacian (−∆) m , and we can derive various caloric smoothing estimates.The convolution f * g of two functions f, g ∶ R n → R is defined byprovided that the integral exists. It is well known that the convolution f * g inherits the regularity of both f and g, in the sense that if, say,In this article, we study the regularizing properties of the convolution in the scales of Besov spaces B s p,q and Triebel-Lizorkin spaces F s p,q . Having in mind that the parameters s and p describe the regularity, resp., integrability properties of f ∈ A s p,q , A ∈ {B, F }, it is natural to expect that the implication f ∈ A s p1,q1 , g ∈ A u