In recent years, informed consent has been suggested as a way to deal with risks posed by engineered nanomaterials. We argue that while we can learn from experiences with informed consent in treatment and research contexts, we should be aware that informed consent traditionally pertains to certain features of the relationships between doctors and patients and researchers and research participants, rather than those between producers and consumers and employers and employees, which are more prominent in the case of engineered nanomaterials. (...) To better understand these differences, we identify three major relational factors that influence whether valid informed consent is obtainable, namely dependency, personal proximity, and existence of shared interests. We show that each type of relationship offers different opportunities for reflection and therefore poses distinct challenges for obtaining valid informed consent. Our analysis offers a systematic understanding of the possibilities for attaining informed consent in the context of nanomaterial risks and makes clear that measures or regulations to improve the obtainment of informed consent should be attuned to the specific interpersonal relations to which it is supposed to apply. (shrink)