Introducing "confidence creep": a novel kind of creep. Confidence creep refers to the extension of perceived scientific certainty from one sense of a term to other senses of the same term. To explain confidence creep, I refer to and differentiate it from the existing concepts of "significance creep" (Manson) and "concept creep" (Haslam). In this context, the general phenomenon of "creep" refers to changes that extend the range of content that is associated with a particular term. Using the case example of "epigenetics," I highlight the covert nature by which it operates and the problems it causes for reasoning in bioethics. The concept of confidence creep helps capture ethically salient impacts of divergent understandings of epigenetics. While confidence creep may be a particular concern for bioethicists due to the interdisciplinary nature of the field, it can also apply to anyone making claims involving specialist scientific terms or concepts that have been translated across academic fields or from academia into other sectors. In the case of epigenetics, critical engagement from scholars, physicians, policymakers, science communicators, and the public is necessary to guard against confidence creep and temper the uptake of health claims that involve problematic appeals to epigenetic science.