Milk provides a way of thinking about how the body is enacted in science, policy and popular culture. This paper follows the currents of moral and biomedical epistemologies circulating around milk, including via notions of inheritance, the practices of wet nursing, and emerging scientific knowledge about the health-related benefits of breastfeeding. By situating milk’s flows historically and culturally it shows how constructions of milk production, lactation, and infant feeding have long served as a ‘cultural signal’ of prevailing conceptions of bodies and social identities. In so doing, it explores the simultaneous power of milk as both a source of dispositional and somatic health, and an index of customary forms of unity and division. A focus on breast milk further contributes to augmenting and expanding recent debates about the biology-society nexus in science and technology studies (STS), anthropology, and sociology. Seen within biomedicine today as a carrier of somatic signals about the environment, the article reflects on how milk is bound up in the responsibilisation of women’s bodies and the internalising of potential risks to the health of their offspring. This implies an unlimited agency for women in averting health risks and in future-proofing their children to be better than well, elides the socioeconomic, and environmental forces pragmatically limiting this assumed agency, and the distinct lack of material and inter-personal support for the perinatal period in many nations.