The issue of formalizing skepticism relations between argumentation semantics has been considered only recently in the literature. In this paper we provide a twofold contribution to this kind of analysis. First, starting from the traditional concepts of skeptical and credulous acceptance, we introduce a comprehensive set of seven skepticism relations, which provide a formal counterpart to several alternative notions of skepticism at an intuitive level. Then we carry out a systematic comparison of a significant set of literature semantics (namely grounded, complete, preferred, stable, semi-stable, ideal, prudent and CF2 semantics) on the basis of the proposed skepticism relations.