Chemicals are characteristic of chemistry education practices at all educational levels. The aim of this study is to explore teachers' didactic rationales when reasoning about the use of chemicals in their teaching practice. Experienced upper secondary chemistry teachers in Sweden were interviewed about their considerations regarding why, when, and how they use (or do not use) chemicals, in particular, hazardous chemicals. A qualitative content analysis was conducted. The results reveal that the teachers' reasoning about their uses of chemicals is multifaceted and draws on student learning, teacher perspectives, traditions, and practical conditions. The results may be used to support teachers' didactic analysis when planning practical work in chemistry education, both in preservice teacher education and continuous professional development.