Article 3(1)(c) of Regulation (EC) No 528/2012 (BPR) defines ‘active substance’ as a substance (or a microorganism) that has an action on or against harmful organisms. But what is a substance, whether active or not? According to the definition given under Regulations (EC) No 1907/2006 (REACH) and 1278/2008 (CLP), a substance goes beyond a pure chemical compound defined by a single molecular structure, but includes multiple constituents: all those that cannot be separated, such as additives (if any) and impurities.