I. Introduction: The SiS concept In the last months, mainly triggered by German authorities, a new topic related to REACH emerged: “substance in substance”, or short “SiS”. The concept of SiS is to regulate substances which are part of other substances. Especially, the German Federal Office for Chemicals (Bundesstelle für Chemikalien) at the Federal Institute for Occupational Safety and Health (Bundesanstalt für Arbeitsschutz und Arbeitsmedizin) favors suc